Stellar Evolution | Astronomy Cast: Recent Episodes
Stellar Evolution | Astronomy Cast
A star like the Sun only lasts about 10 billion years and it becomes a red giant and finally a white dwarf. This is catastrophic for some of the planets, consumed by the expanding red giant star. But most survive. What happens next in the long, slow cooling to the background temperature of the Universe?
Show Notes* Stellar lifecycle: Sun → red giant → planetary nebula → white dwarf * Fate of Earth: likely engulfed or stripped to a molten core * Mass loss reshapes planetary orbits (planets may drift outward) * Planetary nebula: gas, radiation, and drag affect surviving worlds * White dwarfs: hot, dense cores supported by electron degeneracy * Second-generation planets can form from debris disks * Possible habitable zones near white dwarfs (tidally locked planets) * White dwarf evolution: cooling, crystallization (“diamond core”) * Observations: debris, planetesimals, and planets around white dwarfs * Long-term future: shrinking habitable zone, fading system * Ultimate fate: cold stars, lost planets, and a dark, cooling universe
Transcript:Fraser Cain:
AstronomyCast, episode 789, what happens to planets when the stars die? Welcome to AstronomyCast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. I'm Fraser Cain.
I'm the publisher of Universe Today. With me, as always, is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of Cosmic Quest.
Dr. Pamela Gay:
Hey, Pamela, how are you doing? I am doing well, and I glitched it exactly the way it drives you crazy.
Fraser Cain:
No, no, no, just to be clear, it does not drive me crazy at all. I never even noticed until one of our viewers mentioned this exact tick that you have. And now, as a supportive co-host, I had been mixing it up just to sort of kick you off of your routine, and clearly, we go back to the standard, and you're back on your routine.
So we need to go deeper, I think. I need to make the introduction and me asking you how you are more complicated. Things are going to get weird, and that's fine.
We need to pass through the valley of fire before we can come out the other side. New, reforged, refreshed. So we've both seen Project Hail Mary.
Dr. Pamela Gay:
Yes, I found it deeply endearing. I am not going to buy the Lego set, but I may 3D print my own Rocky, because Rocky is the best.
Fraser Cain:
I mean, when you see the making of, and you see them running that guy around as a puppet, that's crazy how much of that movie is practical. Are you going to love this movie? Yes.
Are you going to have some scientific quibbles if it runs across something that you're actually very good at? Yes. But that's fine.
It's a good movie. I really enjoyed it. Anywhere can do no wrong.
Keep it up, Andy. I hope you get your Star Trek series. A star like the sun only lasts about 10 billion years, and then it becomes a red giant, and finally a white dwarf.
This is catastrophic for some of the planets consumed by the expanding red giant star, but most survive. What happens next in the long, slow cooling to the background temperature of the Universe? Alright, the Sun.
Give us the future history of the Sun.
Dr. Pamela Gay:
I love that concept. Our Sun, oh man, it's going to shed a whole lot of mass, and exactly what happens depends on how much mass gets shed. So we know for certain that it's eventually going to shed its outer layers, form a planetary nebula.
The remaining part of the core is going to collapse down, get supported through what's called electron degeneracy pressure, which is basically all of the electrons going, poly exclusion principle, poly exclusion principle, and pushing each other out.
Fraser Cain:
You can hear them. Literally, you can hear them yelling out if you're close enough to a neutron star.
Dr. Pamela Gay:
I don't recommend it. Not a neutron star. A white dwarf.
Neutron star have neutron degeneracy pressure, so they're yelling something different.
Fraser Cain:
Different sound.
Dr. Pamela Gay:
Yeah, yeah.
Fraser Cain:
Exactly.
Dr. Pamela Gay:
So one of the problems with the mass loss is depending on how much mass loss occurs, you have planets moving different amounts. So it is entirely possible that the Earth will be consumed when the Sun bloats up into a red giant star, or due to mass loss, it might move outward and escape that fate. Now the problem is you now have all of this material all over the place, and it's going to create drag.
And so now you have a new problem. You have hopefully escaped the red giant stage. You are now living within a planetary nebula.
You're now living within the shredded outskirts of your star. And what is left over is a white dwarf that shines very brightly in the ultraviolet. And ultraviolet can vaporize rock.
Fraser Cain:
Right. And I know that the temperature, like when the, like the core of the Sun, the temperatures are in the millions of Kelvin. And then the star dies, blasts out those outer layers, bloats up as a red giant, consumes definitely Mercury and Venus.
Maybe Earth, we're still not sure. Mars will probably survive. The ice moons of Jupiter will enter the habitable zone, which I always think is so cool.
And then it will, you know, puff out a layer, shrink back down, and then it'll do it again, puff out a layer, shrink back down. And then, as you said, you get that planetary nebula that's around it that is always so cool. What sort of, what decides the final orbit of the planets?
Dr. Pamela Gay:
It is a combination of what is the final mass of the white dwarf, what is the final velocity of each planet, and is their orbit stable or is it decaying as they interact with material around them?
Fraser Cain:
Right. So if you, if you decreased the mass of planet Earth, like if you just opened up a wormhole and just started siphoning away mass from Earth to some other part of the Universe, what would happen to the orbits? Our orbit would not noticeably change.
No, no, but what happened to the orbits of the satellites? Because now they're orbiting something with less mass.
Dr. Pamela Gay:
So it's GMM over R squared there, so the total force goes, hold on, you asked me a question and my brain just broke. So if their velocities stay constant, so they move outward.
Fraser Cain:
Right, their velocities stay constant, so they move outward.
Dr. Pamela Gay:
Yes.
Fraser Cain:
Right, yeah. So there is less gravity that is pulling on them, or there is less distortion of space time that they are maneuvering through, and they still have that same velocity, therefore they will spiral outward.
Dr. Pamela Gay:
Yes, and this is where the mass loss of the Sun means if it loses enough mass, we move far enough outwards that we escape the expansion. However, if there's drag on our system, depending on the amount of drag compared to the amount of mass loss, we can move back inward. This is one of the ways they consider for creating hot Jupiters, and so these are things we need to think about.
Now, in general, the interplay between mass loss and the orbital velocity of planets is considered second order to the amount of mass lost by that star, but these are still things that keep me awake at night.
Fraser Cain:
Right, and I think it's really important to say that we are not unharmed. In the best case scenario, we are the planet Earth is mangled, believe, right? It is, you have spent maybe 4 billion years, 5 billion years in a temperature regime that is beyond the boiling point of water on the surface of the Earth, all of the oceans have boiled away, that you have now, you have spent time maybe in the atmosphere of the star as it was expanding as a red giant.
That wasn't fun.
Dr. Pamela Gay:
Our world is a crispy critter.
Fraser Cain:
Yeah, yeah. So it may still exist as a sphere of rock, but it is not unharmed. That's why we have all moved out to the ice moons of Jupiter to watch the mayhem unfold.
So then we settle into what is this long future balance, and what does that look like?
Dr. Pamela Gay:
So that little tiny Earth-sized basically star in the center, dead star in the center, while it screams electron degeneracy pressure, it starts out super hot, but it's not generating heat any longer, which means that over time, it's going to cool off. And there's going to be this really neat evolution of what's going on close to that star. So some really cool work came out last year, I think.
Fraser Cain:
I think I reported on this. I was going to bring this up, but you weren't going to.
Dr. Pamela Gay:
Yeah, Jordan Stekloff led the work where a really hot white dwarf vaporizes the rock around it. But then as it cools, that rock reforms a new dust disk. And so you have this disk that ends up forming.
It's not like protoplanetary disk the way we think of protoplanetary disks. But as we look for objects around white dwarfs, we don't find anything around hot young ones. We find dust disks around medium-aged ones.
And as they cool, we start to find these planetesimals. And that is just super cool to me.
Fraser Cain:
Right. It's planetary formation round two, that the material is following the same laws of physics that cause the dust to come together into larger and larger objects. And then eventually you get, as you say, planetesimals forming around the white dwarf.
And so it is another chance. So there's hope. One other piece of research that I found really interesting that I also reported on was that there appears to be this pause that white dwarfs go through in their cooling process.
Yeah. That kicks in. They crystallize.
Yeah. They crystallize. And then that sort of crystallization, it's changing.
I forget what exactly it is. It's like the boron in it is like changing the shape of the crystallization. And so it's cooling halts for billions of years before finally it kicks off again.
And so you actually end up with a long lived habitable zone that it does appear to match this sort of process of planets forming around it that will last you for quite a while. So it's interesting that you can, and like the habitable zone around the white dwarf is like four times the distance from the earth to the moon. So it is very close, like a million kilometers away from the star.
You will be tidally locked. Yes. And yet the habitable zone is there.
Dr. Pamela Gay:
And what gets me about this process is we're starting to learn of all these weird crystalline things that go through metamorphic changes. And we see the same thing with water ice where there's different kinds of water ice and energy will go to phase changes in how the water ice is formed at various temperatures. And so this idea that you have to think through how does the crystalline structure mediate cooling processes is something that I never learned to wrap my head around.
Now, admittedly, I was in school as an astrophysicist, we have hydrogen, helium and everything else. But when we discussed white dwarf cooling, this wasn't something we were considering in the 90s. This is a new concept.
And it's really cool to see how it plays into our understanding of the evolution of stars around us.
Fraser Cain:
And this isn't theoretical work at this point, like we are seeing examples of white dwarfs with the signs that we're talking about around them. We are seeing them with planetesimals. We are seeing there are white dwarfs with planets.
There are white dwarfs with clouds of debris around them that have been detected and observed with James Webb and others. So this is not just a theoretical possibility. This is confirmed in some of the white dwarf systems that have been observed so far.
So what do you think is kind of the best case scenario for the future of a star system like the sun?
Dr. Pamela Gay:
I mean, it depends on best case to whom. If you're asking for humanity...
Fraser Cain:
No, we're cooked.
Dr. Pamela Gay:
We're cooked. Yeah. Yeah.
Fraser Cain:
We've moved to Proxima Centauri. That's the best case for us.
Dr. Pamela Gay:
Right. Exactly. Yeah.
And so, I mean, Proxima Centauri is tiny. It's going to have its own different issues, but it will live forever. But it's going to last five trillion years.
Yeah. Yeah. Yeah.
Yeah. I think massive amounts of mass loss making a truly beautiful planetary nebula that the remnants of humanity can study the formation of would be pretty cool.
Fraser Cain:
From inside?
Dr. Pamela Gay:
Yeah. Yeah.
Fraser Cain:
Or from Proxima Centauri?
Dr. Pamela Gay:
From Proxima Centauri. And what gets me about things like planetary nebulae is they can be huge. They can be light years across.
And so, this is a nebula that would reach out and touch someone. And Proxima Centauri will no longer be the closest star at that point. Our separations will radically change.
So, we could be on some completely different star, just to be entirely clear. But this idea of humanity getting to watch the evolution of a planetary nebula, and so all the mass you can possibly lose, please do it and let future scientists enjoy.
Fraser Cain:
Yeah. I mean, we definitely have some questions about what are the conditions that are required to give you those really cool planetary nebulae. Is it a binary system?
Like, do you need a second star to whip up the material to create those interesting shapes? Or do you just get it with a single star that's just puffing out those outer layers?
Dr. Pamela Gay:
And planets, what kinds of planets are necessary? And yeah, it's complicated. And we want to know all the things.
Fraser Cain:
And what happens to the outer planets? I mean, we're obviously focused on Earth. It's cooked, crispy critter.
What happens to the outer planets, the Jupiters, the Saturns, Uranus, Neptunes?
Dr. Pamela Gay:
So, they migrate outwards. And so, Jupiter will end up being stripped of some material because it's gassy. It doesn't hold on to its outer layers extraordinarily well when it's getting blasted and the temperatures are changing.
Fraser Cain:
So, it might go through mass loss as well.
Dr. Pamela Gay:
Yeah. Yeah. More like mass stripping.
Fraser Cain:
Right. Which would have repercussions for its moons.
Dr. Pamela Gay:
So, it's complicated. The outer planets are all gassy, icy objects that can undergo structural changes in the process. So, we will have asteroids that are probably okay.
They will just get melty on the surface. We have Mars, which any ices it's still got are going to be gone. It'll probably lose what little atmosphere it has left.
The icy moons will cease to be icy moons out at the distance of Jupiter. I'm not sure about Saturn. I'd have to run the maths to see just where Saturn lands in the equations.
Fraser Cain:
Right. But this migration, and I mean, can this migration cause mayhem in the universe? We know early on in the solar system there appears to be a migration.
This is the Nice model. Do we go through this second phase where what was once this sort of perfect clockwork balance now gets out of balance again and there's another chance for mayhem?
Dr. Pamela Gay:
There is another chance for mayhem. There will definitely be additional mayhem, but luckily there are fewer worlds available for that mayhem. So, early on we had at least a few extra planets that we no longer have.
The one that smashed into Earth to form the Earth moon as it is today.
Fraser Cain:
Yeah, whatever happened to Uranus? Yeah, yeah.
Dr. Pamela Gay:
Yeah. Venus is another one that had something bad happen. Jupiter's core is fluffier than it should be, so something creamed into it.
Fraser Cain:
Yep. And who knows what went into the sun?
Dr. Pamela Gay:
Yeah. And so there were a lot more objects around to create mayhem in the first iteration. In the second iteration we will have had a lot of stuff obliterated, we'll have a lot of stuff made smaller.
So yes, mayhem will occur at a smaller scale.
Fraser Cain:
All right. So the sun has died, gone into its red giant phase, gone to its white dwarf phase. Now it is cooling down.
There's a cloud of debris around it that has maybe formed into some kind of planetesimal, maybe even within the habitable zone. And so a future Proxima Centauri expedition will be able to build a base and examine what it's like to live inside a white dwarf system down in the future. But the sun has died, but now what happens to the sun and what happens to the planets that are around it from this point on?
Dr. Pamela Gay:
So anything that snuggled in at that kind of Earth-Moon distance to this new white dwarf will have formed there out of the dust debris cloud and is going to be tiny. So sure, that group from Proxima Centauri can set a cup of water on it and watch as it sublimates away into pure gas because there's no atmosphere on that little tiny world. Right.
So habitable only refers to the temperature. It doesn't pay attention to things like pressure that also matter if you want to have life outside of spacesuits.
Fraser Cain:
They're solar system engineers. Okay. They drag something inward.
And are able to import, yeah, they've imported a whole bunch of comets and have dumped them onto the world and built up, thickened the atmosphere.
Dr. Pamela Gay:
And added mass.
Fraser Cain:
And added, well, I mean, I know that even, this was like a paper that I reported on that even like 1.5 meters per second is enough escape velocity for you to be able to hold on to an atmosphere. I'm not sure.
Dr. Pamela Gay:
Right. But those planetesimals are probably smaller than that.
Fraser Cain:
So as you say, they add mass, they mash a bunch of them together, they do some solar system engineering. I guess where I'm going with this is if you did have the right kind of world, would it be a stable, habitable place that you could live on for now billions of years?
Dr. Pamela Gay:
I wouldn't say billions of years. These things do cool down over time where your ultraviolet heated white dwarf has to cool down to allow those planetesimals to form. But that cooling is just going to keep going and keep going until eventually you're no longer, that habitable zone is going to snuggle up closer and closer and closer until you can touch the surface of the star.
I do not recommend doing this.
Fraser Cain:
Yeah.
Dr. Pamela Gay:
Because the gravity is still there. Yeah, yeah. So, but ignoring the gravity, the white dwarf in the fullness of time will cool off and it will also evaporate in the fullness of time if we're correct about protons not being stable.
Fraser Cain:
Right. Right. Or even Hawking radiation.
Right. We talked about that, right? Yeah.
That it appears that if Hawking radiation works for black holes, it probably works for anything and everything.
Dr. Pamela Gay:
Yeah. That has energy.
Fraser Cain:
And that in a roughly the same time scale, you'll get all of the white dwarfs evaporating away and, you know, any planet, anything, right, anything with mass will evaporate. But before that, like we've got this white dwarf that is cooling down, but you still have the interactions between the solar system and the rest of the galaxy. So what happens next?
Dr. Pamela Gay:
So you're getting dragged around as you get colder and colder and you literally end up being a source of darkness except for gravitationally lensing things you happen to pass in front of.
Fraser Cain:
Right.
Dr. Pamela Gay:
And, and there's, I mean, this is as boring as it gets. You have cold planets orbiting a cold star. Everything is cold and your only ability to, to raise excitement and make your existence known is through gravitationally lensing background objects.
Fraser Cain:
Well, so, so the thing that's, that I think people don't realize is that you're still experiencing these gravitational interactions with the other stars in the, in the galaxy and they are going to be plucking away your planets one by one. Yes. And it takes about a hundred billion years and you will lose all of your planets but one.
So whichever one, yeah, yeah, this was a, this was a paper that I report on. So you'll lose all your planet. It takes about 10 billion years, I'm sorry, a hundred billion years.
And then you're down to one planet. And this process is going to happen in all of the star systems. So they're all going to use up their star forming material.
They're all going to die. They're all going to then give up their planets. And then over even deeper time, all of those stars will be kicked out through three body interactions of the galaxy itself.
And so eventually you'll just be left with the supermassive black hole and all the stars have just been all kicked out and all of their planets have all been kicked out. And then it takes about five trillion years for the, for the white dwarf to just cool down to the background temperature of the universe.
Dr. Pamela Gay:
I love this story of the universe building structure, building structure, building structure, removing the structure.
Fraser Cain:
Yeah. And they're just, they're just dismantling it all. You built your Lego set and now you're, you're throwing all the pieces away and you're back to square one.
Dr. Pamela Gay:
No, don't throw them away. Scatter them to the wind.
Fraser Cain:
You scatter them to the wind. Yeah. You've thrown them all in.
You waited for wind gusts and you just throw pieces of Lego out into the wind and let them carry. This analogy is falling apart. But, but, but the point is that, that in the end there will be the sun and it will be a, a ball of material, right?
Roughly the size of the earth, the background temperature of the universe, it will probably have one planet that is tidally locked to it and, and it has been kicked out of the Milky Way and it is wandering the universe until Hawking radiation makes it dissolve into a, just a soup of particles and energy in the background temperature of the universe.
Dr. Pamela Gay:
The exciting part is it will at least be a giant diamond.
Fraser Cain:
So there is that. Yeah. Yeah.
For a while there, the sun will be the world, the, the universe's biggest diamond.
Dr. Pamela Gay:
Well, I mean, there could be other ones out there.
Fraser Cain:
There will be bigger diamonds. Yeah.
Dr. Pamela Gay:
Yeah.
Fraser Cain:
From other stars. Yeah. There's the theoretically largest possible carbon white dwarf.
Yes. But still. Yeah.
Dr. Pamela Gay:
The future is weird.
Fraser Cain:
It really is. Yeah. Yeah.
Isn't it weird? I always, I always remark on this, how when we think about deep time, we feel this, uh, this sense of sadness in our we about this future that we don't stand a chance of experiencing, right?
Dr. Pamela Gay:
Well, it's, I, I think it's kind of like when important buildings are lost, even if we've never visited them, it's just sort of like energy went into the formation of that. Don't destroy it. And, and so in, in the end times, as we currently expect it to go, everything that we know will end up becoming nothing more than diffuse energy in, in this, this cold rip of space time.
But it's that intermediate point where things are getting flung hither and yon and all the spiral galaxies are getting taken apart. All the elliptical galaxies are getting taken apart. Galaxy clusters are, are just becoming lumps of diffuse glow.
Um, I mean, it's, it's, it's kind of both sad and silly at the same time. It really, your Lego analogy was excellent until you said you throw them out.
Fraser Cain:
Okay, fine. You mail them off. You mail the pieces off to friends around the world.
Dr. Pamela Gay:
Well, I really just like imagine this angry, small individual in the center of a room throwing with varying amounts of energy, all of the pieces until there's just this diffuse cloud of, of Legos.
Fraser Cain:
So there you go. Uh, so what we're saying is there's a chance.
Dr. Pamela Gay:
There is a chance. There's always a chance.
Fraser Cain:
Yeah. All right. Thanks, Pamela.
Dr. Pamela Gay:
Thank you, Fraser. And thank you so much to all of our Patreons out there. And I'm now going to mispronounce your name as my way of saying thank you.
Our show wouldn't be here without the amazing support of so many of you over at patreon.com slash astronomy cast. This week, I would like to attempt to thank by name the following people, and I'm sorry for what I'm about to do to the pronunciation of your names. This week, I'd like to thank Abraham Cattrell, Alex Cohen, Alexis, Andy Moore, Bore Andro Bart Flaherty, Benjamin Davies, Brian Breed, Brian Cagle, Claudia Mastroianni, Dan Fiennes, DeSastrina, Dwight Ilk, Ed, Eron Zegrev, Eric Lee, Evil Melky, Flower Guy, Jeff McDonald, Glenn McDavid, Helga Bjorkhag, Jarvis Earl, Jean-Baptiste Lamartine, Jim of Everett, Joe Holstein, John Esdraseth, Jonathan H.
Starver, Jonathan Poe, Justin Proctor, Justin S., Katie B., Kimberly Reck, Larry Zotz, Mark Scheer, Masa Herleyu, Michelle Cullen, Mike Dogg, Nick Boyd, Noah Albertson, Paul L. Hayden, Paul Lowell, Pauline Middlelink, Philip Grand, Philip Walker, Red Bar is watching, Rill, RJ Basque, Ryan Omery, Steven Coffey, Steven Miller, Tim Garish, Travis C. Porco, William Andrews.
Thank you all so very much.
Fraser Cain:
All right. Thanks, everyone. And we will see you next week.
Dr. Pamela Gay:
Bye-bye, everyone.
LIVE SHOW
Main sequence stars spend most of their time being… normal. Fusing hydrogen into helium in their cores. Producing radiation. But as their stockpiles of hydrogen run out they switch to other fuels, starting to climb the ladder of the periodic table of elements. And this is when things get weird. As we get more and more observations of the cosmos, our understanding gets more detailed. In this episode we look at all the ways a star can die and the updates that we've learned in the past 20 years of Astronomy Cast.
Show Notes* What are evolved stars and how stars leave the main sequence * Main sequence basics: hydrogen fusion and stability * Role of mass in determining stellar evolution paths * Helium ignition & shell burning (helium flash) * Evolution stages: red giant → asymptotic giant branch (AGB) * Mass loss and its impact on a star’s final fate * End states: white dwarfs, neutron stars, black holes * Formation of planetary nebulae and stellar remnants * Case study: Cat’s Eye Nebula and evolving understanding * White dwarfs: composition, cooling, and crystallization * Cosmic timescales: stars vs nebulae vs galaxies * Observing stellar evolution through changing nebulae
Transcript:Fraser Cain:
AstronomyCast, Episode 787, Evolved Stars. Welcome to AstronomyCast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. I'm Fraser Cain, I'm the publisher of Universe Today.
With me is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hello, Pamela.
Dr. Pamela Gay:
Hi, how are you doing, Fraser?
Fraser Cain:
I'm doing well. See, since someone said, oh yeah, Pamela always says, I'm doing well, like always has that stutter there. I've decided I'm just going to mix up the intros every time.
You need to get out of the rut. You need to be shaken up and just exist in this sort of place where you can no longer find any firm footing, that the future will be unbounded and unstable. This is my guarantee.
At least the greetings I provide to you will be anything but a certainty.
Dr. Pamela Gay:
As long as it's shaken and not stirred, we're good.
Fraser Cain:
There you go. So this is an interesting anniversary for me, which is that we are at about the one-year mark from when Universe Today removed all of the advertisements from the website. Or when I removed all the advertisements from the Universe Today website, anyway, we went ad-free across our entire existence and instead just relied on people to join our Patreon.
And we're doing great. And by great, I mean, after I made that pronouncement and said, okay, this is what I want to do. Otherwise, I'm going to start laying off people and I said, I'm just going to remove the ads because they're now, the value is down, whatever, 70, 80%.
Let's switch to Patreon. If we can cover that shortfall, then I'll just keep the business running as usual. And we got an amazing response.
People joined. The number of patrons jumped up to exactly where it needed to be, which was kind of crazy. And I was anticipating it to quickly drop off.
And instead, there's definitely a lot of people who sort of were there for that month just trying to help us out. But then it's been sort of refreshing at a level where our income across the entire year is now just absolutely predictable. And in a way that we can have no, like I was able to redesign the website.
It's completely, it's so fast. No ads in the newsletter, no ads in the podcasts, the absolute minimum amount of ads that YouTube will let us do on YouTube. It's great.
It's amazing. And I just, like, it's amazing how free I am to just think about how can we provide great content. I sit and look at, I built a tool that lets me slurp in all of the journals from ADS as well as Archive, as well as the NASA technical report server.
And then I just go through those 600 papers every day. And I don't think one second about managing advertisements and search engine optimization and AI slop and any of that kind of stuff. So yeah, I know there's some overlap here where people are both on, you know, are my patron as well as the Astronomy Cast patron and maybe the Cosmic Quest patron.
But just like, thank you so much. You did this, you know, you are participating at whatever level and it has made a dramatic change. I haven't had to, I've let the writers write as much as they want.
Our coverage has gotten better and it feels like it's this perfect balance. And teachers tell me that they can use my stuff in the class and they just, they don't feel embarrassed for the ads of sexy ladies showing up, you know, like who knows what you'll get when you have various Google ads showing up on your stuff. So it's just, it's the best possible world.
And I feel like now I'm unstoppable. So thank you. Yeah.
Dr. Pamela Gay:
Yeah. And if you folks want to do the same thing to Astronomy Cast, we still have about 20% of our revenue coming in through ads. And I'm answering emails from about 10 people a week who are not happy with the ads and not happy with the network role.
Yeah.
Fraser Cain:
Yeah. Yeah.
Dr. Pamela Gay:
And so it's like, it's beyond my control what podcast they're going to send you to at the end of ours.
Fraser Cain:
But it can be. It can be. In your control.
Dr. Pamela Gay:
Yeah.
Fraser Cain:
Yeah. All right. Main sequence stars spend most of their time being normal, fusing hydrogen into helium in their cores, producing radiation.
But as their stockpiles of hydrogen run out, they switch to other fuels, starting to climb the ladder of the periodic table of elements. And this is when things get weird. All right.
So let's first like set a baseline and just talk about the main sequence phase of stellar evolution.
Dr. Pamela Gay:
So stars for the most part, and this is an important caveat that almost always gets left out. For the most part, stars start out their lives burning just hydrogen in their core and they hang out there burning hydrogen in their core for millions to billions of years. But the most massive stars actually get to burning some heavier elements right off the bat because they are that big.
So what we see is if we do a plot of the brightness of the stars versus the color of the stars, the temperature of the stars, there is this really cool line that goes through it that is this is all the stars that have finished collapsing down from being protostars have begun to completely and stably balance themselves between light pressure outwards and gravity inwards. And that is where they're going to stay for the initial era of their life.
Fraser Cain:
Right. And this is the thing that you see when you look at the Hertzsprung-Russell diagram. There's a big line that is in the Hertzsprung-Russell diagram where all the stars, all the main sequence stars live.
Dr. Pamela Gay:
Yes. And this is, we call it the main sequence. And it's yeah, it's just where most stars are because that's where stars linger the longest.
So statistics.
Fraser Cain:
Yeah. And those other forms, I mean, there's like the CNO cycle, like there's other cycles that can happen in like a tiny fraction, even in the sun, but are happening more commonly in the bigger stars. But the one that we're looking at mostly is, is this, uh, this, the traditional hydrogen to helium.
So then sort of what leads to, you know, when would you call a star evolved? Is that, is that like a polite way of calling a person old? Um, oh, you're a very evolved person.
Very mature.
Dr. Pamela Gay:
It's definitely postmenopausal stars. We'll go with that. So, so the, these are the stars that, uh, their core has run out of its initial fuel.
And so that initial thing that it was doing to generate light and support itself against gravitational collapse has stopped. And the first thing that ends up happening is the star will collapse down a little bit because again, the thing it was generating light from has stopped. Now that process of collapsing will heat it up more in the core.
Um, that whole pressure volume relationship that we learned in high school works for stars. And you will then end up with a shell of hydrogen burning around that core and you will eventually end up with helium burning in the core going to neon. And then eventually a whole bunch of, of additional, depending on the mass of the object, a whole bunch of additional, uh, elements climbing up through all the various relationships.
So, right.
Fraser Cain:
So this, so this idea of it creating these shells. So is this sort of that because the, the temperature in the core has like, you need a minimum temperature in the core to even get fusion, like out of 4 million Kelvin or something like that. Temperature and pressure.
You need both. Yeah. Temperature and pressure.
Yes. Yes. But that is sort of like where you define the smallest possible, like the 0.08 solar mass red dwarf. That's when it comes online as a main sequence stars is when it is able to reach that temperature and pressure in the core. And that when you run out of the hydrogen in the core, you switch to the helium burning thing. That changes the temperature in the core, which then brings more hydrogen fuel online in addition to the fusion that's happening from the helium.
Right. Is it, am I understanding this right?
Dr. Pamela Gay:
So, so the shells and the core, you can end up with them going at a different points. So there's this, this thing called the helium flash when that core ignites. So you have the initial collapsing down a shell around the core of hydrogen will ignite as it gets the correct hydrogen and pressure density temperature thing.
And then that core ends up igniting as, as everything reaches a new set of temperatures.
Fraser Cain:
In this case, it's the helium in the core can now fuse. Okay. And then, but this must like something must happen at this moment when the, when now the helium has come online in addition to this, this hydrogen shell, what happens to the star?
Dr. Pamela Gay:
The star bloats out radically. And so now you have the main red giant branch, you have the asymptotic giant branch. You have all these different places that stars go to live and, and where they are on this plot depends on exactly what's going on.
And so our Larry's my favorite star, we're going to return to them often. They're chugging along on this flat line after they've undergone that helium flash. We have moving up, we have that hydrogen shell burning and exactly what's going on again is going to depend entirely on the mass of the star.
I'm just going to keep repeating that dependency on the mass of the star. And one of the things that foils us on the regular basis is we, we have a pretty good understanding of the initial mass function that stars will format. We know there's not that many big ones that end up forming out of the fragmenting molecular cloud.
We know there's a gazillion little ones that form and then they undergo mass loss and exactly how much mass loss is something we're still trying to come to terms with. So you end up seeing wild phrases like stars, less than eight masses should eventually become white dwarves, but then between eight and 20 masses, they all become neutron stars. Well, neutron stars like are less than two and a half solar masses, right?
Fraser Cain:
So where'd the rest of the mass go?
Dr. Pamela Gay:
And it's all the mass loss, right? And, and so we used to not understand exactly how much mass loss was going down. And as we realized it was like the majority of the stellar mass got lost, it, it caused wild changes to how we understood stellar evolution.
Fraser Cain:
So, so then like, yeah, so, so say a star like our sun, it goes through that mass loss process and ends up with like half its mass, right? Like essentially the core is all that remains and the rest of the, the outer layers have all been sloughed off into, into space. So, so you get this, I mean, you essentially just described the red giant phase.
Does this take a while or does this happen like when that helium ignites, does it happen very quickly?
Dr. Pamela Gay:
So quickly as a matter of, of perspective. So our sun will spend about 10 billion years as a main sequence star burning through its hydrogen. It will then spend tens of millions of years in each of the subsequent phases.
So we're going from billions of years just chewing through hydrogen to then in, in the grand scheme of stars dying is going to rapidly both give off its matter and go through the CNO cycle, becoming a, a little diamond of a core surrounded by mass. It's going to exhale into the surroundings before becoming a carbon nitrogen, oxygen rich white dwarf star.
Fraser Cain:
But it takes longer than 10 million, like you said, the various cycles, like it has to go through a whole bunch of phases, puffing out, shrinking back down, puffing out, shrinking back down. And so, I mean, like I had seen that it was on the order of hundreds of millions of years for that whole process to wrap up, to go through all the different phases. Yeah.
Yeah. Okay. Yeah.
Yeah. Yeah. Yeah.
Closing in on a billion. Okay. So then, so, and I think, you know, we've done a whole episode on, on red giants and I, I wouldn't be surprised if we've done an episode on aurora lari, but probably, probably, I don't know.
Who knows? We'll check. Someone will tell us.
But, um, but, okay, so you, you get this place. So essentially much more heat is coming out of the core of the star. The star is, is then bloats out because it, the, the, that balance between the gravity that's pulling inward and the radiation pressure, the pushing outward is now totally shifted.
Dr. Pamela Gay:
Yes.
Fraser Cain:
And now the star is much larger, but also kind of cooler and also cooler. But, um, so what brings it back down again?
Dr. Pamela Gay:
Um, it's not so much that it shrinks down again as it just gets rid of its atmosphere over time and it's just left with the core.
Fraser Cain:
Oh, that's amazing.
Dr. Pamela Gay:
Right.
Fraser Cain:
Right. So it's not like it is because there are those variables, like the cataclysmic variables, things like that, where they are, you know, they are pulsating, but in this case, no, you're, you're puffing out and then you're just letting this, this go into space. Goodbye.
Dr. Pamela Gay:
Yeah. Yeah. It goes, it goes away.
Fraser Cain:
And there are phenomenal pictures of stars where they're surrounded by just this, you know, diffuse glow of material that the star ejected in various previous generations. Although it takes, it takes so long that a lot of this stuff's gone. Like it's, it's only the last couple of sheds can you actually see?
Dr. Pamela Gay:
Well, and, and what we're starting to learn is, um, what we're able to see depends on when we're looking and how much things have had a chance to cool or self-destruct. All these stars are going to undergo massive amounts of mass loss in their end days. So one of the rides on that for the Hubble Space Telescope to get built was actually to figure out what the heck are planetary nebulae from the ground at that point when they were building the Hubble Space Telescope, we didn't really have adaptive optics.
We didn't have eight meter and bigger telescopes. So we didn't have ground-based resolving abilities to, to see all the fabulous details. We just knew there were these smudged out blobs of color that appeared to be a variety of different gases at different ionization levels.
And so Hubble starts looking at these things and is finding in the cores of many of them white dwarf stars, ultraviolet emitting hot young white dwarfs. And so you have two things going on in these situations. The material is still drifting away.
As it gets further and further away, it's not getting heated up as much. And then that white dwarf in the core is also cooling down. So planetary nebulae surrounding white dwarf stars are created in the final days of smaller mass stars that don't go supernova and end up with the core of the star left behind.
And we know it's the core of the star from looking at its composition. And what we're seeing is the outskirts of the star that just got exhaled. But the story gets more complicated because we also have discovered that some of the hottest stars, the most massive stars that also undergo massive amounts of mass loss have around them what look like planetary nebulae.
Yeah. Yes. And this is because they're giving off ultraviolet light.
Fraser Cain:
So what's it? It's the cat's eye nebula picture.
Dr. Pamela Gay:
The cat's eye nebula. Yeah.
Fraser Cain:
Yes. Is that what is that? Put this into your mind.
You want to talk about? Yeah. Okay.
All right.
Dr. Pamela Gay:
That's still annoying me.
Fraser Cain:
Like, yeah.
Dr. Pamela Gay:
You learn planetary nebula have white dwarfs in the core and then you learn you're totally wrong.
Fraser Cain:
And yeah. What's the neutron star doing at the middle of it? Yeah.
Right. So, so then, I mean, we talked about main sequence stars, but, and, and sort of their process of shedding out this material. And then of course, now I learned the inspiration is this just incredible picture of the cat's eye nebula released from James Webb combined with information from Hubble and other telescopes.
And it's just, it's an insane picture.
Dr. Pamela Gay:
Euclid. Yeah.
Fraser Cain:
Yeah. Yeah. It's just an incredible picture.
And so, and so now maybe the, the giant stars are making planetary nebulae as well.
Dr. Pamela Gay:
That are also short lived, but for a totally different reason. So in these cases you have massive stars, these, these can be 30 solar mass stars that are eventually going to become neutron stars. They can be more than 30 mass stars are eventually going to become black holes.
And some of them will just eat themselves entirely and nothing will be left, but whatever their ultimate fate, they have formed on their way to that fate. This glorious temporary nebula, and then they go supernova all over it. So when we're looking at things like the Crab Nebula, it is entirely possible that not only are we seeing the shock waves from the supernova moving out, but that material that is being disrupted is something that once looked like the cat's eye nebula.
And this idea that you can go through multiple forms of exquisite beauty in death with these stars from, from something that was shaped by jets, by the, the existence of companion stars, by the existence of a planetary disk, all shaping how material is given off, creating what looks like a 1980s spirograph of nebulosity.
Fraser Cain:
Yeah. It's interesting. You know, I had this sort of realization about how young these remnants are, planetary nebulae and supernova remnants that, um, you know, when we look at galaxies, you can be looking at galaxy and it's a little look roughly the same for billions of years.
You look at star clusters. Okay. Now these things are going to look kind of similar for a hundred million, a hundred million years, 10, you know, the really young ones like please, okay, now maybe 10 million years, the really, really young star forming regions, maybe they're in the millions of years.
You're looking at the Orion nebula and you're going to see that, that really heavy nebulosity before the stars, you know, maybe 10 million years. But when you look at things like say the veil nebula, various supernova remnants, planetary nebula that you might be looking at things that are only say tens of thousands of years, thousands of years old. And it's this moment, this very short moment of time when this thing is, is released and then it fades away into the, just the interstellar sort of gas and dust that's out there.
All of the, the forces, the winds, the interstellar wind that's blowing on these stars is just adding up and eventually fades this thing away into the background. And so everything we look out and see, we're seeing fairly recent events.
Dr. Pamela Gay:
We can see them changing with time. That's the thing I love, like the crab nebula there, there was an activity when I was a student where it would give you a, a pair of images of, of the crab nebula and you measure the angular separation between the edges of the nebula and the stars. And you could calculate the rate of expansion in arc seconds per year.
Well, we've, we've been now looking at these objects for going on a hundred to 140 years.
Fraser Cain:
Yeah.
Dr. Pamela Gay:
And, and this is allowing us to really see both how they're expanding away from their source of heat. And then we can look out and we can start to get a sense of how white dwarfs cool and how supernova cool. And it's such a singular moment in time that these things exist.
Fraser Cain:
So I just want to continue along the story of this stellar evolution. So these stars, they go through this point where they're using different, different fuel, they're using different elements, they're fusing different kinds of elements in their cores, walking up the periodic table of elements to whatever is their final set point and letting out these outer layers into space. How does this end for a, for a star more like the sun?
And then we'll talk about the, how it ends for the bigger ones.
Dr. Pamela Gay:
So for smaller stars, you end up with when we look out at white dwarfs, we often see them that are carbon, nitrogen, oxygen rich. These are your CO white dwarfs. They come from stars similar to the sun.
As you start getting to smaller and smaller stars, you eventually at the smallest little we'll actually have had a chance to die larger red dwarfs. That's a really dumb way to phrase all of that, but they will eventually run out of fuel in the fullness of time. We haven't seen this occur yet, but when they do, they'll just collapse down into being pretty much a solid helium blob.
And then we do see objects that are smaller than the sun and have had enough billions of years to run out of hydrogen in their core. And they've just collapsed down into basically helium white dwarfs. So we just see the moral equivalent of charcoal that's still glowing.
Nothing is keeping it lit and it's just going to cool down over time. They're coals. That's what we're looking at.
Fraser Cain:
I've been working on the story about this. So white dwarfs, they start out at 150 Kelvin.
Dr. Pamela Gay:
Ultraviolet. Yeah.
Fraser Cain:
And yeah. And so that temperature corresponds into the ultraviolet. And so they're very, very bright.
And then they cool down. Neutron stars start at 600,000 Kelvin, which is why they are in the X-rays when they first start out.
Dr. Pamela Gay:
And what's cool is these are crystals, folks.
Fraser Cain:
Yeah.
Dr. Pamela Gay:
And as they cool, their crystalline structures rearrange. And so we'll see jumps in temperature as they go from one crystalline structure to another crystalline structure. And the energy changes how it's being.
It's like when something goes to changing phase instead of just cooling off.
Fraser Cain:
It's cool. Yeah.
Dr. Pamela Gay:
It's actually very hot.
Fraser Cain:
Yeah. It's very cool. Now, that's hot.
When they talk about the cores of these stars, that they are literally diamonds, that they really are like one big crystalline diamond. So yeah, super cool. Awesome.
All right. Thanks, Pamela.
Dr. Pamela Gay:
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Fraser Cain:
Nice. All right. Thanks, everyone.
And we will see you next week.
Live Show
You think the Sun is a terrifying ball of fire and fury? Wait until you learn about today’s topic: Wolf-Rayet stars! These are massive, dying stars hurling their outer layers out into space before detonating as supernovae. Big stars live brief lives, and Wolf-Rayet stars are the punctuation mark we see before things go supernova.
Show Notes* What are Wolf-Rayet stars? Massive, short-lived stars near the end of their lives * Extreme properties: + Temperatures: 30,000–200,000 K + Strong stellar winds and intense mass loss * Historical discovery and early confusion with helium spectral lines * Powerful convection brings carbon, nitrogen, and oxygen to the surface * Massive outflows enrich space with carbon (dust/“soot”), seeding future stars and molecules * Formation of temporary planetary nebulae around massive stars End-of-life scenarios: + Core-collapse supernova + Pair-instability supernova + Direct collapse into black holes (“failed supernova”) * Binary systems create complex structures (spirals, shells) via colliding stellar winds * Connection to gamma-ray bursts (GRBs) and hypernovae * Example systems: + Gamma Velorum (naked-eye Wolf-Rayet star) + WR104 (potential GRB candidate, not Earth-threatening) * Role in cosmic chemistry: key sources of organic-building elements * Rare, rapidly evolving objects—understanding continues to evolve with new observations * Future discoveries driven by surveys and AI-powered data analysis
TranscriptFraser Cain:
AstronomyCast, episode 786, Wolf, Rye, Stars. Welcome to AstronomyCast, our weekly, facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. I'm Fraser Cain, I'm the publisher of Universe Today.
With me, as always, is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hello, Pamela.
Dr. Pamela Gay:
You didn't ask me how I'm doing, and I don't know what to say.
Fraser Cain:
I know.
Dr. Pamela Gay:
Okay, other than hello, have you seen a bear yet?
Fraser Cain:
No. No bears yet. No.
Oh, well.
Dr. Pamela Gay:
But you still have daffodils?
Fraser Cain:
Pine martin. No, no daffodils yet. Pine martin crocuses.
Dr. Pamela Gay:
Okay.
Fraser Cain:
And our various flowering fruit trees are about to flower. So we're about to have the flowering cherry festival here on my property. So apart from that, no, it's good.
But we're going through all of the things that we have on my spring calendar. I think I mentioned this years ago, that we put down a calendar of all of the momentous events that happened. So you don't just have four seasons, you actually have about 50.
And a bunch of them are showing up a lot earlier. So we had the frogs going berserk about a week early. The crocuses are up a little early, but it is sort of interesting.
I mean to keep track of them, and so we can see how the dates change from various events happening. But yeah, yeah. And the big thing of course is the herring are spawning, which is like just search for herring spawn Vancouver Island, and it will blow your mind.
It is the largest biomass movement on earth. Bigger than, will the beast, it's bigger than anything. It is out of this world.
And when it happens, it changes our landscape, changes the beaches, changes the oceans, the wildlife everywhere. It's next level.
Dr. Pamela Gay:
That's kind of amazing and also very gross simultaneously.
Fraser Cain:
Yes. Yeah. Yeah.
But let's just say that spawning herring means that everything on the beach is covered, in some cases, multiple feet of material.
Dr. Pamela Gay:
Yeah, yeah. That's the correct euphemism.
Fraser Cain:
Yeah. Yeah. You got to wear boots to walk through what's on the beaches.
So yeah.
Dr. Pamela Gay:
Wellies. Everyone needs wellies.
Fraser Cain:
Yes. You think the sun is a terrifying ball of fire and fury? Wait until you learn about today's topic.
Wolf-rayet stars. These are massive dying stars hurtling their outer layers into space before detonating as supernovae. All right.
Wolf-rayet.
Dr. Pamela Gay:
I love the fact that we both pronounce it very differently because I always said Wolf-rayet I don't speak French though.
Fraser Cain:
Yeah. Yeah. I do believe I'm going to go with you.
I'm pronouncing it in a way that a French person might want to pronounce it. Yeah. But definitely not rye-yet.
Dr. Pamela Gay:
No. No. That is, that is completely wrong.
That T just pretend it's not even there.
Fraser Cain:
Yeah. Yeah. I've heard people say it.
So yeah.
Dr. Pamela Gay:
But anyway, so what are they? They are giant stars that are contemplating going boom. These are one of the early massive astrophysics confusions.
One of my favorite details about these stars. So, so basic details we didn't know initially. They are 10 to 35 solar radii.
They are 30,000 to 200,000 Kelvin in temperature. They have- Hold on.
Fraser Cain:
Hold on. Hold on. Like, wait a second.
Like the radii, I think people can wrap their heads around it. That's big.
Dr. Pamela Gay:
Yeah.
Fraser Cain:
It's not Beetlejuice big, but they're hot. And so they are hot and, and big, but, but actually fairly dense, but, but that temperature.
Dr. Pamela Gay:
Uh huh. I can't wrap my head around it.
Fraser Cain:
Yeah. The surface temperature of the sun is about 5,800 Kelvin, 5,800 Kelvin. And say the temperature again.
Dr. Pamela Gay:
Uh, 30,000 to 200,000 Kelvin.
Fraser Cain:
200,000 Kelvin on their surface.
Dr. Pamela Gay:
Yeah.
Fraser Cain:
That's bonkers how hot these things are. Yeah.
Dr. Pamela Gay:
And so they're massive. They don't live very long because big stars have brief lives. But when they were first found, we didn't know any of that.
When they were first found in the middle of the 1800s, we didn't even know helium existed. This is, first of all, one of the things that's deeply confusing to me. It took a long time to discover helium because helium does not work and play well with other things.
So helium is like, I'm off here being helium. You shall not bond with me. And because of this, we didn't have spectra for it as early as we had spectra for many other elements.
So when these stars were first found and people took spectrum of them because we were learning how to do that, it was a cool thing to do. They saw these sets of spectral lines that were reminiscent of hydrogen but were not hydrogen. And it would take tens of years for helium to be discovered to figure out what was going on.
Oh, yeah.
Fraser Cain:
Isn't that wild? That's interesting. Yeah.
Yeah. So they knew that there was another chemical that was next in the number of protons, but not necessarily next in the order of finding them because actually helium is a pretty tricky non-reactive gas to find.
Dr. Pamela Gay:
And they hadn't gotten to that. They knew there had to be another one in terms of electrons yet. They were still figuring this stuff out.
They just knew there's this pattern of spectral lines that looks like what we think is hydrogen, but we're not sure yet. It's similar. And so a lot of work had to be done to make that connection.
It's just, I love the fact that we identified these stars before we identified one of the most prominent elements in the universe. And these are stars that are at the end of their lives and weirdly behaving in some ways a lot like tiny M-dwarf stars. So they're out there convecting wildly.
And this also changes how they appear. Our sun, it has a core that's undergoing nuclear reactions. It has a radiation zone.
It is a convection zone. You don't generally see the enriched material from the center making it to the surface of the sun. It's just not a thing that's happening.
With Wolf-Ray stars, we see an atmosphere that is enhanced with carbon, nitrogen, oxygen, and that enhancement is due to the convection that is able to dredge up materials. And so you have massive convection going on. You have bloated out atmosphere going on.
You have massive amounts of wind and mass loss. And all of this is, in terms of the convection, very similar to what we see with tiny stars where you have that fully convecting atmosphere. And I just love that it wrapped around on itself.
There's just a lot of little cool details about these stars to kind of fall in love with before they explode.
Fraser Cain:
So there was a paper that just came out, or there was a news release that came out from Hubble. I think it was the Cat's Eye Nebula. Yeah.
And that has a Wolf-Ray star in it, in the center. And yet it's creating a planetary nebula. And traditionally, sort of my understanding was a planetary nebula came from main sequence stars like our sun, that at the end of their life, they become a red giant, they blow out their layers.
But actually, you can get them even from these extreme objects.
Dr. Pamela Gay:
And this is one of those things where we are always going to be rewriting our understanding. And we now need to do an episode updating our understanding of planetary nebula, because this is a new understanding. Planetary nebula are formed when stars of existing, it used to be we used to say stars of lower mass, are exhaling their atmospheres at the end of their lives.
We didn't think through the fact that not every planetary nebula is going to have a white dwarf in its core, because all of that material has come off of what used to be a 10 or less, nine or less solar mass star. What we're now realizing is there are temporary planetary nebula around some of these massive objects that are undergoing mass loss. And Wolf-Ray is one of these massive objects undergoing mass loss.
And so here, this is temporary. That star is eventually going to most likely undergo either parainstability or standard I ran out of fissionable, fusible material in my core, I shall explode now kinds of supernova. And that supernova is going to shred that nice, pretty planetary nebula we know today.
Fraser Cain:
And then you're right. So then you're left with a regular old supernova remnant.
Dr. Pamela Gay:
Exactly.
Fraser Cain:
Right. So you just sort of, you know, you might get a parainstability. I think our audience is perfectly comfortable with the idea of a core collapse supernova, right?
It runs out of fuel in the core, burns all the way up to iron, fusion energy collapses, the star implodes, you end up with some kind of either neutron star or black hole remnant and a supernova. But the parainstability, I don't think people are that familiar with this process. So what's going on in a parainstability supernova?
Dr. Pamela Gay:
So in the core of the star, it's running so hot that gamma rays are being produced. And as these gamma rays pass through the outer layers of the star, they're going along, interacting with things and causing pairs of, that's the name, pairs of electrons and positrons to be created.
Fraser Cain:
Right. So it's building antimatter in the star.
Dr. Pamela Gay:
And the combination of the electron and the positron existing side by side, they can then go, hi, we are a matter antimatter matched set. We shall annihilate now and release energy photons. And those photons from the annihilation are able to push outwards, creating the light pressure that supports the star.
Fraser Cain:
And they're also gamma rays. Exactly. Exactly.
Dr. Pamela Gay:
Now, the catch is that positron, electron, putting it into existence and taking it out of existence through annihilation, there's time that that takes. And if you generate positron, electron pairs too fast, you have too much of the gamma ray, too much of the light pressure going into particle, antiparticle creation, and it's not decaying fast enough to create the light pressure to support the star. So you end up with a pile up of these positron, electron pairs, not enough light going out and the star's like, you're not holding me up anymore, bud.
And the star just collapses.
Fraser Cain:
Right. But it also vaporizes.
Dr. Pamela Gay:
Right. I mean, it's a little bit of both. It's that Loki gif, both.
Fraser Cain:
Yeah, because I mean, you're not getting all of those additional elements up the periodic table. Exactly. You're getting this totally different process that blows the star apart.
And how these actually proceed at the highest levels, we still don't even fully know. Sometimes you get a black hole in the end, other times you don't.
Dr. Pamela Gay:
And we can't see the systems that go straight to black hole unless we know the star ahead of time. And so understanding, are we right? Is it correct that some of these most massive objects just calmly become black holes without going through the supernova process?
Fraser Cain:
Yeah. So there is like this fairly recent research that we reported on quite a bit. Actually, I'm going to be interviewing people from this work, but that they found one of these un-novas, where there was a star there and then the star is just gone.
It brightened up and then it's gone. And there's no supernova, even though the progenitor should have gone off as a supernova. And it seems like what defines whether you get the supernova or not is the amount of neutrinos that are being blown out of the center of the star while this process is happening.
So if you get enough, then the neutrinos, even though they never interact with anything, they're still interacting enough with the infalling material that you get the supernova. But if you don't have enough neutrino production, then the thing just collapses in on itself as a black hole. And it could be that it's the neutrinos that act like the brake that stops the process of it just imploding into a black hole.
But your mind just boggles at this idea that you just had this star that maybe had hundreds of times the mass of the sun, and then it just went boop, it's gone.
Dr. Pamela Gay:
And the understanding that we have of these objects is rapidly, rapidly evolving. So anything we say we understand today, as especially Ruben comes online, our understanding could change. One of the things that got me preparing for this episode is back in 2017, we only knew of 30 of these in our galaxy.
And so just the rate at which we're finding them, the rate at which we're coming to understand their mass range, the rate at which we're coming to understand the possible ways at which stars die, the fact that we've only realized that they can sit in the cores of planetary nebula recently, all of these things, we're only going to add to this changing knowledge. And that's kind of cool. Rare, short-lived phenomena are the wild west where we still have the most to learn.
Fraser Cain:
So play out this sort of time of the mass loss, where it is going through this point where it's shedding out all of these outer layers. I mean, I think people are familiar with different flavors of variable stars and sort of compare and contrast it to what happens with the sun. Like when the sun goes through its final days, turns into this red giant, and then it oscillates between a smaller star and a bigger star and will sort of throw this material out.
How does that compare to what happens with one of these Wolf-Ray stars?
Dr. Pamela Gay:
I think it's important to realize that Wolf-Ray stars are kind of the big star version of the gamma ray end of the electromagnetic spectrum. At a certain point, everything above a certain mass is called a Wolf-Ray star when it's evolved. So these things range in initial mass from about 30 solar masses to hundreds of solar masses.
That means they don't all behave exactly the same in terms of how long it takes them to do things and how wildly they do things. Looking at it more generally, you have a star that has evolved out. It's no longer burning hydrogen in its core.
It has pretty much run out of hydrogen. This is an evolved star. It's living millions of years, tens of millions of years, basically.
And as it has hit this evolved stage, it has winds that are going hundreds of kilometers per second. And so we have massive winds that are causing those emission lines that we see in the spectra to be broad. These are the kinds of winds that we expect in things that have massive inflows.
In this case, it has massive outflows. It's its own light pressure that is driving this, not gravity. And that is new and amazing for these kinds of objects.
They can be in binary systems.
Fraser Cain:
Right. I wanted to talk about that. Yeah, but just most massive stars are in binary systems.
And so extra mayhem.
Dr. Pamela Gay:
Right. There was a JWST image that recently came out that sees these layers of gas around a binary pair of Wolf-Ray stars. And what you get with these multi-star systems is you have high speed winds coming out from the star.
Those winds collide. Now, the way to visualize this is you have two sprinkler heads that are going around and around each other. And so they're creating both a spiral and a water slams and falls straight down, except it just compresses because there isn't gravity pulling straight down in space.
This creates an amazing shell structure where you can say, oh, yes, this is how we get planetary nebulae. It's rich in carbon. Carbon is something that will hold on to temperature in ways that hydrogen doesn't.
And so these are things that will glow in the infrared in ways that are perfect for JWST. Right.
Fraser Cain:
Yeah. So you're talking about how these produce a lot of carbon. Yeah.
You know, and another way to describe this as soot, that if you could go and collect this stuff, it would be very similar to the kinds of stuff that you would sort of find on the inside of a chimney, right? The smoke that's coming out of a campfire, same kind of stuff.
Dr. Pamela Gay:
The technical phrase is amorphous carbon. Yeah. Don't ask me to spell amorphous.
I'm just deeply amused that like carbon has so many specific names for its structures, but it's got a lot of bonds. It does. It really, really does.
And it likes to bond, unlike helium. And so these stars are producing carbon that bonds into amorphous carbon molecules. It bonds into other kinds of molecules.
We do see things like buckyballs in space. But the majority of this is the kinds of dust that then goes on over time to get spread throughout the galaxy that ends up seeding molecular clouds, that ends up seeding the creation of all of these weird and amazing molecules, amino acids that we find between the stars. And so we're in this situation where we have massive stars born fast, die fast.
You only find Wolf-Ray stars in the youngest of star forming regions and the most massive of star forming regions, because the number of stars you have of a high mass depends on the initial mass function, which depends on the mass of the system. So if you want to get more than one of these, you need to have a whole lot of mass. Yeah.
We do find them in collections. There are a few examples for this out there. And they're undergoing massive amounts of mass loss.
They're going to undergo supernovae, which means they're going to scatter that material everywhere. But in the interim, it's out there being a thermal blanket to the stars, holding on to that heat, radiating away energy. It's just really cool.
While being really warm.
Fraser Cain:
Yeah. I mean, one of the incredible discoveries that astronomers have been making recently is just how much of the precursor molecules for life are being found just forming in deep space. You're seeing organic molecules.
You're seeing amino acids. We're seeing alcohols, sugar, basic sugars, things that are like gum. Formaldehyde.
Yeah. It goes on and on and on. And and now it's like I think things that are like protein precursors as well, like it just every little bit and piece of what all the building blocks of what life needs.
And carbon, of course, is is key to all of them. And and it really feels now that these are the these are the source of a lot of the carbon that's out there, that you have these massive stars dying, throwing all this carbon into space, that you're not having to wait for these massive stars to die as supernovae. And it's different from what you get from colliding neutron stars, for example.
They give off the heavier elements, stuff that's beyond iron in the periodic table of elements.
Dr. Pamela Gay:
And we've always known that carbon, nitrogen, oxygen were coming from the atmospheres of stars. We misattributed how much comes from what mass star, thinking a lot of it came from smaller stars. We were wrong.
And and this is your reminder that all it takes is one big whale doing something to bias the system. All those little guys, they're trying their hardest. They're just not going to make the same dent.
And and these are the whales of stars.
Fraser Cain:
So what is a relatively nearby what are some examples of some of some famous Wolf Ray stars that that people can can be familiar with? So, I mean, the most massive star that we know of, which is our one thirty six A is a Wolf Ray star. Yeah, it's Wolf Ray star.
That's in the Large Magellanic Cloud. It is like more than 200 solar masses. It is ludicrous.
Dr. Pamela Gay:
And it's that star forming region in the Magellanic Cloud that is where we find a whole bunch of these. Yeah, there's a bunch of them in there. That I know of, there's only one that's naked eye visible and it has a really cool name.
It is Gamma Velorum. It is this really cool shock looking nebula inside of a greater region of nebulosity. That's the neat thing that happens when you're looking at things in star forming regions that still have unused material.
And and so you can see if you look at this through a variety of different filters, there's pictures all over the Internet that you have the the super hot ultraviolet light from the Wolf Ray star heating the surrounding nearby material associated with its mass loss. And then around it is the material not yet incorporated into a star that is glowing due to being a star forming region. In general, Wolf Ray stars have a huge influence on the nebulosity of their systems.
You can look at a system and see the scattered light from these Wolf Ray stars no matter where you look in the nebula, the scattered light carries that that spectral signature in new directions. But when you're looking for something that has that cool pair of reflection nebula and light from scattering, these stars really do the best.
Fraser Cain:
What is their connection to Gamma Ray Bursts?
Dr. Pamela Gay:
So, as we discussed many times before, Gamma Ray Bursts are one of those things we're still trying to figure out. So Gamma Ray Bursts, we think that hypernova are a special kind of supernova that are either caused by a fast rotating individual star undergoing core collapse supernova or a binary system where you have a massive star feeding material onto a companion star that has a strong magnetic field. And whatever the situation is, you have this resultant strong magnetic field that acts as a funnel for high energy particles in the early moments of the supernova.
And it is the particles heading down that funnel that are the Gamma Ray Burst. And so you will see with long, long period Gamma Ray Bursts, they can be up to tens of seconds, a couple I think have been over 100 seconds. And these longer period ones, you see the Gamma Rays, you look for the optical afterglow, it fades quickly.
And then at the location where you saw the Gamma Ray Burst, a supernova remnant will appear a few days later because the brightest part of the supernova actually comes from particle decays that take a few days to get their light together.
Fraser Cain:
So, you know, people are always worried about Gamma Ray Bursts and which is the which is the closest one to us? Not a concern. Well, the closest one that we know of is this one called WR104 and it is a Wolf Ray star.
And it is about 8000 light years away, which is still like definitely in the kill zone, like if it's pointed at us. It's not. But it's not, although when you look at the pictures of it, it's a little spiral that does appear face on.
But apparently the the angle is off of us enough.
Dr. Pamela Gay:
It's just enough.
Fraser Cain:
Yeah, that it's not going to not going to strike us. But this is an example which, as you mentioned, right, you've got the star, it's clearly got a binary companion because you're seeing this spiral shape and that that there's something about the interactions between the big star and its companion that sets up the conditions for a potential Gamma Ray Burst. But but as as you said, this is all new territory.
We're still trying to figure this out. And thanks to Vera Rubin, we're probably finding a couple of night now.
Dr. Pamela Gay:
So, yeah, it's absolutely wild. What is starting to occur? And I deeply appreciate the fact that it's AI all the way down where they're using machine learning algorithms to process the data in real time, split it up across multiple data brokers, and then people are using additional AI to triage the data.
The data brokers have its AI all the way down.
Fraser Cain:
A good a good use for AI. Yeah, I actually just interviewed somebody who runs one of the data brokers, the Noir Lab data broker. So I've got a lot of information in my head about that right now.
All right. There you go. Wolf Ray stars wrapped.
Thanks, Pamela.
Dr. Pamela Gay:
Thank you. And thank you so much to all of our patrons over on Patreon dot com slash astronomy cast. There are so many of you and I mangled your names so ruthlessly, but not on purpose.
Fraser Cain:
No, it's best half the fun.
Dr. Pamela Gay:
Yeah, it's true. If you too would like to hear me destroy your name, join us at patreon.com slash astronomycast. We're able to do astronomycast thanks to the amazing support of people like you.
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Live Show
Magnetars are a special type of neutron star with physics that defy comprehension. Magnetic fields so powerful they could strip you apart at an atomic level. But, where do they come from? So many mysteries to uncover about magnetars. Back in December 2004, a gamma rays washed out cameras and zotted satellites as a star on the other side of the Milky Way shifted around its magnetic fields. Magnetars are violent that way. In this episode of Astronomy Cast, Fraser and Pamela take on this tiny terrible monsters.
Show Notes* What are Magnetars? * Neutron Star Origins and Supernova Formation * Magnetars vs Pulsars and Regular Neutron Stars * Extreme Magnetic Fields (≈10¹⁵ gauss) * The 2004 Magnetar Gamma-Ray Outburst * Possible Formation Mechanisms (massive stars, mergers, binaries) * Why Magnetars Are Rare and Short-Lived * Soft Gamma Ray Repeaters and Detection Methods * Starquakes and Magnetic Field Reconfiguration * Magnetar Cooling and Evolution into Neutron Stars * Dangers of Magnetars: intense radiation and atomic disruption nearby * Observing Neutron Star Activity with Modern Instruments * The Mystery of Magnetar Origins and Lifetimes
TranscriptFraser Cain:
Astronomy Cast, Episode 785, Magnetars. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. I'm Fraser Cain.
I'm the publisher of Universe Today. With me, as always, is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hey, Pamela, how are you doing?
Dr. Pamela Gay:
I am doing well. I've had the weirdest two weeks, and I caught COVID for the first time.
Fraser Cain:
Oh, no. How are you feeling?
Dr. Pamela Gay:
I'm still snuffly, and I'm not convinced it isn't allergies, because I've been snuffly for a month, and I haven't had COVID.
Fraser Cain:
Yeah, but you did test positive for COVID.
Dr. Pamela Gay:
Yeah.
Fraser Cain:
That's, you know.
Dr. Pamela Gay:
Yeah.
Fraser Cain:
You could be, like, not experiencing much of the disease, and you're also enjoying allergies. So, yeah.
Dr. Pamela Gay:
Right. I think that is indeed what happened. And, yeah, there were six of us at a little tiny event that everyone tested before they arrived, but the current version of COVID has a two-day incubation period.
So, yeah. On Wednesday, having all gotten together on Sunday, six of us tested. Yeah.
So, it was a thing. It was a thing. So, thank you, everyone, for your patience, for your well wishes, for putting up with my fever dreams posted to the internet.
Right. But I have a question for you. Okay.
In the spring, have you had the first bear sighting of spring yet?
Fraser Cain:
No, no. I don't even have that in my calendar. I have a calendar of all of the key events that have happened, and we're kind of marching through First Robins, what we call the frog chorus, where the frogs just go berserk at night.
First Thrush, First Crocus, but I haven't written down First Bear, but they're soon. They typically show up around within the next month or so. So, I'll let you know when I see First Bear.
Dr. Pamela Gay:
Okay. That sounds awesome. We have hit the owls are definitely wanting to get it on season, and it sounds like the owls sound like monkeys this time of year.
Fraser Cain:
So, which kind of owl do you guys have around you? We have barred owls. You have barred owls.
Yeah. So, we have them as well, but they're invasive here. Although, I mean, how do you say a bird that flies around is invasive, right?
Birds just go where they want to go. But yeah, we have barred owls. I think I've mentioned this in the past.
My way of finding barred owls is you listen for the robins going berserk. Yeah. So, if you hear a whole bunch of robins just losing their minds, and they're usually clustered around a barred owl, and so you can just go into the forest, listen for robins.
You guys have robins there too, right?
Dr. Pamela Gay:
We do, but they stick to the ground. That's their domain.
Fraser Cain:
Well, yeah. So, if you go into the forest, you just listen, and if you hear a whole bunch of robins really angrily chirping, they've got an owl locked in on an owl, and they're just harassing it. Yeah.
Dr. Pamela Gay:
All right.
Fraser Cain:
Let's move on. Magnetars are a special type of neutron star with physics that defy comprehension. Magnetic field so powerful, they could strip you apart at an atomic level.
But where do they come from? So many mysteries to uncover about magnetars. All right.
So, what is a magnetar?
Dr. Pamela Gay:
They're angry little monster neutron stars. Right. These are sometimes pulsars, not always.
They are definitely neutron stars, so they're about 20 miles across, about 30 kilometers across, size of Manhattan Island. They have some of the most powerful magnetic fields kicking around.
Fraser Cain:
I have this number in my head, actually.
Dr. Pamela Gay:
Yeah. Go for it.
Fraser Cain:
Well, it's 10 to the power of 15 gauss.
Dr. Pamela Gay:
Okay. I do not store that number. Thank you.
Fraser Cain:
So, the Earth is, I think, about three gauss.
Dr. Pamela Gay:
Yeah.
Fraser Cain:
So, that's ludicrous, right?
Dr. Pamela Gay:
The thing about them that lives rent-free in my brain is in December 2004, a magnetar on the other side of the core of our Milky Way from us, so basically half a galaxy away, got the neat idea to rearrange its magnetic field, and it released such high-power gamma rays that it saturated telescopes pointed in completely different directions, orbiting telescopes. That's crazy. Yeah.
Yeah. And these things have slowly, we're understanding, are responsible for soft gamma ray repeaters. They may be responsible for ultra-fast radio bursts.
They just do lots of things, and they're violent about it.
Fraser Cain:
Yes. Yeah. Yeah, absolutely.
So, then you say that they are neutron stars. We know that you get neutron stars from the death of a massive star. It runs out of fuel, implodes, the material, the infalling material builds up at the core.
You get this neutron star.
Dr. Pamela Gay:
Yeah.
Fraser Cain:
And then when they are first formed, they are rapidly spinning because they have the combined angular momentum of all of the material of the original star, and so they are spinning, they are pulsating, putting out these radio waves.
Dr. Pamela Gay:
And they're not pulsating, just to clarify language. Yes, sorry. So, pulsating stars are actually like changing in radius.
I love these buggers.
Fraser Cain:
Yes.
Dr. Pamela Gay:
Yeah. These have a misalignment between magnetic field and rotational axis, and as the pull of the magnetic field whips around, it gives off a jet that we see as a burst of radio signal.
Fraser Cain:
Right, right. Continue, sorry. Yeah, no, and that is a pulsar.
Yeah. And that as a pulsar ages, it is bleeding off its rotational energy through gravitational waves, it slows down, and eventually it stops being a pulsar and just switches to being a regular old neutron star. Right.
So this is the normal behavior of the neutron star. You start off as a pulsar, you end up as a neutron star, and then who knows what happens.
Dr. Pamela Gay:
And the normal formation mechanism also needs to be addressed because as far as we're concerned, your run-of-the-mill, everyday neutron star comes into existence when a massive star, so something nine to ten solar masses or larger, a main-sequence star, fails to lose enough mass in its old age. And so instead of collapsing politely down into being a white dwarf, it undergoes some sort of supernova explosion. And what's left behind is a core of neutrons that have so much mass that the gravitational push on the object causes electrons and protons to go, can't separate any longer, and they merge into neutrons.
So that is how neutron stars should form.
Fraser Cain:
Right, right. And so then that is the normal, and that is not what we're talking about today. We're talking about magnetars, which are different.
And weird. Yeah, and weird, and weird. So I guess, how would you sort of just describe physically a magnetar as a comparison to a neutron star?
How do we sort of think about that?
Dr. Pamela Gay:
Well, so they are both neutron stars.
Fraser Cain:
No, I know, but why do they have a name, right? Why are they different?
Dr. Pamela Gay:
So pulsars are sometimes rotating as much as a thousand times a second. Magnetars are looking more like one to two times a second. There are pulsars that are magnetars.
But they have this massive magnetic field that pulsars don't normally have. And it's looking like maybe one in 30 pulsar neutron stars have a magnetar phase in their life. And so the question becomes, is it one in 30 massive stars going supernova that end up forming a magnetar due to some sort of conservation of netohydrodynamics and magnetic flux?
So that as an object that already had a magnetic field that was massive collapses down, something occurs. Is this just a weird thing that some stars have for other physical reasons? The understanding of how you get this magnetic field is that in the formation of the neutron star, there is a chaotic layer that rearranges itself, which is why we get these amazing star quakes that is responsible for the dynamo inside the magnetar.
But then, so I mean, the thing is pulsars, we normally find in young stellar populations. We find them in star forming regions. We find them in the disks of spiral galaxies.
They go where massive stars are still in the process of dying. But then magnetars are like, no, I'm going to be over here with the old guys. And so that raises the question, and this was magnified, just to use the word magnetic as much as possible in inappropriate ways, by the discovery of a weirdo magnetar with the license plate SGR 0501 plus 4516.
So that's a soft gamma ray repeater. It is on its way through the disk of our own Milky Way. We know we have magnetars.
They blast us occasionally. But it can't be traced back to a supernova remnant. And so the thinking is that maybe there are binary systems where a white dwarf is somehow able to gain mass from its companion in a way that somehow, there's a whole lot of the word somehow involved in magnetar science that somehow causes it to transition from being a white dwarf with electrons and protons just barely holding each other apart with electron degeneracy pressure to in a massive release of gamma rays, but without a supernova, transition into being a neutron star. So we're still figuring out how.
And as science likes to keep showing us, our idea that there's going to be one pathway doesn't necessarily have to be true. So it could be both pathways are possible.
Fraser Cain:
So you mentioned one possible way that magnetars come into existence, that a white dwarf is somehow upgraded into a magnetar. There is another one. I actually recently did an interview with scientists about this, that it's thought that maybe you can have either merging white dwarfs or merging neutron stars and you get a kilonova.
Yeah. But the total mass of the object is still not heavy enough to turn into a black hole. And so you've mashed together the rotation and the momentum of these two, you know, city sized monsters, and you end up with something that is ferocious.
And they did a scan of a believed kilonova event using radio telescopes trying to detect the presence of a magnetar there and they failed. So in that case, it doesn't look like it formed a magnetar, but they're tricky. It's a very tricky observation to make.
And so that is another way. But I mean, we've heard as many theories on magnetar formation as there are scientists.
Dr. Pamela Gay:
Yeah. And it's a transitory thing. So it's not only that not every neutron star is a magnetar.
It's also that only during a temporary, and we don't know is this measured in hundreds of thousands or millions of years, only for a temporary period of time is this what's going on in these stars. Eventually they discombobulate themselves. They go from having these chaotic layers, this high power magnetic field to relaxing that magnetic field and no longer being a magnetar, just being a normal neutron star.
And so that fact that it's transitory makes it even harder to figure out. And that point you made about they're hard to detect, I can't stress that one enough. Unless they're being a soft gamma ray repeater, we're stuck looking for things like Zeeman line splitting and wild polarization and other things like that that are indicating magnetic fields.
And those are hard detections to make.
Fraser Cain:
Yeah. That idea of polarization, I think is a great way to kind of look at it. That when magnetic fields interact with dust and things around it, they can align the particles.
Dr. Pamela Gay:
Yes.
Fraser Cain:
The particles emit radiation. The radiation is polarized. And so you can use a very powerful radio telescope to scan a region and detect this polarized emissions coming from this location.
That was caused by a magnetic field. The more aligned the particles are, the stronger the magnetic field is that's working in that vicinity. But you have to have the particles.
But you have to have the particles. Exactly. Yeah.
Yeah. So you need a certain kind of characteristics to show up for you to be able to make those kinds of observations. That soft gamma ray repeater, can you give me, why do they call it a soft gamma ray repeater?
What's soft about it? Gamma rays are hard.
Dr. Pamela Gay:
Astronomers should not be allowed to name things. Okay. Okay.
Fraser Cain:
Yeah. I believe we have set this as maybe our top rule. On AstronomyCast.
Dr. Pamela Gay:
So someone asked me to name something last week. I was like, no, I'm an astronomer. No.
So hard and soft get used in gamma rays and x-rays to refer to where they are in the spectrum, but also occasionally for how loud they are. Again, we should not be allowed to name things. In this case, it's referring to where they are in the gamma ray spectrum, which admittedly just keeps going forever.
It's sort of like radio goes all the way to the long, gamma goes all the way to the short, but soft means they're closer to x-ray.
Fraser Cain:
Right. Okay. All right.
So they're right on the edge between x-ray and gamma ray.
Dr. Pamela Gay:
Yeah. Right.
Fraser Cain:
Okay. All right. So then, you know, we, and we speculated on a couple of ways that magnetars form.
Do we have any sense of what the future of magnetars look like? I mean, is this a, this is believed to be a temporary phase in the life of a, of a neutron star. So, so, and they're already rotating fairly slowly.
So what do we think the future holds for, for magnetars?
Dr. Pamela Gay:
They become boring lumps of neutrons that are slowly cooling away as, as, um, I mean, neutron stars and white dwarfs, they're dead. And, and that means that when they form, they are ultraviolet emitting super hot cores of stars. And over time, as they radiate away that energy, they're going to get redder and redder.
And we actually have lots of observations showing that white dwarf cooling curve. They're going to go through phase transitions as the crystallization. These are essentially crystals of, of, of particles.
Um, they're going to go through phase changes as they release energy, as they go into more and more relaxed states. And that's the cool thing about magnetars that we don't see with white dwarfs is they start out with a certain amount of chaos in their structure, just because they collapsed down. It's a violent process.
And that misalignment of chunks, uh, that's a higher energy state. And over time, they literally rearranged themselves to be lower and lower energy states. They give off these gamma rays and, and they're, they're cooling and normalizing themselves into just being a chunk of neutrons that are someday going to do like everything else in the universe and deteriorate and become a nothing.
But for now, they're just going to become a cool lump of neutrons gravitationally held together and getting redder and redder over time.
Fraser Cain:
Right. This, this idea of, of essentially star quakes is, is just so cool. Um, that, you know, when you think about this, you know, people talk about a neutron star is a blob of neutrons, but the reality is that it actually has layers like onions and ogres, right?
Yeah. That, that it can then, as it cools down, it can rearrange itself. You get these, these earthquakes on the star.
Dr. Pamela Gay:
You just said onions and ogres.
Fraser Cain:
Yes. Yeah.
Dr. Pamela Gay:
Okay.
Fraser Cain:
They have layers. Okay. Have you not seen Shrek?
Dr. Pamela Gay:
Yes.
Fraser Cain:
Have you not seen Shrek?
Dr. Pamela Gay:
I forgot that line entirely until you reminded me. I.
Fraser Cain:
Ogres, ogres are like onions. They have layers.
Dr. Pamela Gay:
I haven't seen it since 2001. I am sorry.
Fraser Cain:
No, it's fine.
Dr. Pamela Gay:
2002, I guess. Whenever it came out.
Fraser Cain:
You should have just, just let it roll past you and just, you know, one, a tiny part of the audience got my reference and like, ah, nice one, Fraser. And you just had to ruin it for me.
Dr. Pamela Gay:
I did.
Fraser Cain:
I'm sorry. Yeah. Yeah.
Just edit that out, Rich. I don't want everyone to hear it. No.
Um, so, so yeah, this idea that they have these quakes that they will rearrange themselves. You get, and, and there's a, just a great instrument on board the international space station that the nicer instrument that is studying neutron stars and detecting these flashes as neutron stars are, are rearranging themselves and sending out short little, little blasts. And, and so it shows that these things are more active than I think we had described, you know, you call them a piece of matter.
They're just, they're dead. They're dead and dying. And yet in fact, they're not completely dead.
No, they are zombies. Another reference. Um, they're just mostly dead, which means they're partly alive.
Okay.
Dr. Pamela Gay:
Um, where's your white horse? Um, all right. So we have these, these dead stars with their chaotic interiors and their massive magnetic fields.
And when they undergo these, these star quakes, these magnetic field reconnection events, it's, it's all part of a whole that gives off these, uh, gamma rays that vary in intensity. Uh, as I said, back in 2004, one attempted to take out a whole bunch of space telescopes because it Um, and we've seen multiple of these over the decades from our own galaxies believe there's order of tens of these probably scattered about our Milky way. We do see tens, tens, there's not that many, but also estimated there could be, and should be millions of neutron stars out there that were magnetars at some point earlier in their life.
Fraser Cain:
Cause there's a billion neutron stars in the Milky way.
Dr. Pamela Gay:
Yeah. And like I said, it's a super short period of their lives that they go through this. It's, it's sort of like, if you think about some short term in human life, you don't see it very often.
So like that period in time when a child can crawl, but not stand, you don't see that very often because it's such a short period, but even that compared to the length of life of a neutron star is extremely long. Um, so yeah, we're seeing the, the awkward early days of a neutron star. So the period of time when the zombie is still learning to eat brains, I guess.
Fraser Cain:
Right. But, uh, I mean, the fact that we see so few of them tells us that either it's a very rare sequence of events that causes them some kind of specific, unique configuration of a star and a binary companion or two colliding white dwarfs, or, you know, something that is very bizarre. Or as you say, it is a very short phase of the life.
Dr. Pamela Gay:
Both. This is so rare. It's probably both.
Fraser Cain:
Or it is both. A rare event plus a short phase that come together to make these things have such a bizarre and, and short life. Um, and yet they have an oversized impact on their environment for the time that they're in.
And the, the piece that I always like to talk about is this idea that they would tear you apart at an atomic level. So why, why are, why are magnetars going to tear you apart at an atomic level?
Dr. Pamela Gay:
So, so if you get within roughly 600 miles or, uh, uh, 900 kilometers, they, the magnetic field goes, oh, water molecules are, are polarized and, and, uh, they just tear you apart. Atom by atom. Um, yeah, yeah.
That's a thing.
Fraser Cain:
You will decohere.
Dr. Pamela Gay:
Yeah. And, and I mean, you were already having problems because their gravitational field is just that big.
Fraser Cain:
Right. You're experiencing the tidal forces. You're experiencing the radiation.
I mean, you've already had a bad day.
Dr. Pamela Gay:
Yeah. Yeah. So ultraviolet light, it's hot.
Uh, gamma rays, if they're in the process of, of rearranging themselves, that's not an everyday occurrence, but that powerful magnetic field in combination with the powerful gravity, when you get that close and it's, it's the fact that you're taking like 1.4, two solar masses of material and, and crunching it down to the size of Manhattan Island, to the size of greater London. Um, and, and you can get really close to that. And because you can get so close, you experience much larger tidal forces.
Fraser Cain:
Yeah. We talk about that. You know, if you could grab a piece of neutron star and lift it away from the neutron star, even like a, a teaspoon would weigh whatever, you know, the, the many elephants like a mountain, right.
But also would explode. So don't do it. Uh, very cool.
Uh, they're awesome objects and, uh, and, and, and like a genuine mystery. And we don't know right now really what causes them, what begins this, this phase of their lives, what ends it. And, and this is a big chunk of research for a lot of astronomers to get to the bottom of this.
So very cool. Thanks, Pamela.
Dr. Pamela Gay:
Thank you, Fraser. And thank you so much to everyone out on Patreon. Um, reading your names this month, there are so many, I am so grateful.
And I think I mispronounced a third of them, but we're going to go with this. We're going to try this. Astronomy cast wouldn't be possible without the tremendous contributions of people like you this week.
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Thank you all so very much. And if you too would like to hear me struggle desperately to figure out how to say your name quickly, please join our Patreon at $5 a month or up at patreon.com slash astronomy cast. We're very grateful.
My pronunciation is very bad.
Fraser Cain:
All right. Well, thanks everyone. And we will see you all next week.
Dr. Pamela Gay:
Bye-bye.
Live Show
Pulsars are dead stars and fascinating in their own right, but astronomers can use their predictable rotation for exploring the cosmos in a series of amazing ways. We can detect gravitational waves, navigate the solar system, test general relativity and find exoplanets. Pulsars are the time keepers of the sky, with their precise ticking allowing researchers to track gravitational waves, find exotic planets, and study weird relativistic effects. Come learn about how pulsars can be used to explore our universe.
Show Notes* What are Pulsars? * Formation of Pulsars (Neutron Star Remnants) * Pulsar Rotation and Magnetic Fields * Pulsars as Cosmic Clocks * Doppler Shifts in Pulsar Timing * Discovery of the First Exoplanets Around a Pulsar * Rarity of Pulsar Planet Systems * Binary Pulsars and Evidence for Gravitational Waves * Nobel Prize Discovery (Taylor & Hulse) * Pulsar Timing Arrays for Gravitational Wave Detection * Pulsars as Galactic Navigation Beacons * ISS Pulsar Navigation Experiment * Pulsar Glitches and Neutron Star “Starquakes” * Measuring Stellar Mass with Pulsar Binaries * Studying the Interstellar Medium with Pulsars * Pulsars as Tools for Fundamental Physics
Transcript'Fraser Cain:
Episode 784, Pulsar-Powered Science. Welcome to AstronomyCast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know.
I'm Fraser Cain. I'm the publisher of Universe Today. With me, as always, is Dr. Pamela Gay, Senior Scientist for the Planetary Science Institute and the Director of CosmoQuest. Hey Pamela, how are you doing?
Dr. Pamela Gay:
I am well, and I need to know what stage of spring you have encountered already.
Fraser Cain:
Snow and snowdrops. So both. So winter is still here, and yet we also are starting to get, you know, snowdrops and other early spring flowers coming through.
Excellent. Yeah. But I wanted to just mention briefly that many years ago, we were gifted telescopes by Dustin Gibson, and both of us found the telescopes complicated, the software unusable, and we both used them for hanging clothes, I'm sure.
We used the refractor that he gave us on a completely different mount, using an eyepiece and not the camera system. Well, I finally was able to get the telescope operational, get the camera going, get the mount going, and make it all fully functional from my laptop.
Dr. Pamela Gay:
And so now I'm able to sit- A Mac laptop.
Fraser Cain:
That was the thing that foiled me, is like- So I had to buy a, I had a Raspberry Pi kicking around, and I was able to install all the control software on the Raspberry Pi, and then I bolt that to the telescope mount. I put the thing outside, and then I control the telescope from my Mac while I'm just sitting inside, watching the telescope move around. And it's still herky-jerky, and I've got all kinds of problems to it, but it is kind of amazing to be able to use this telescope in sort of what it was originally intended to do.
And hopefully, people very soon will get a chance to just see what I've come up with, because I think you're all going to really love it. In fact, I've ordered a color, like a much fancier, newer, more powerful color camera for the telescope so that I can do live streaming with it in this really cool environment. But it's kind of amazing.
You've got these old projects that you thought you were going to work on, and you just never had the time to do it. And now I'm working my way through some of these projects that were beyond my ability, and hopefully, people will get a chance to see this sometime soon. So stay tuned for that.
Pulsars are dead stars, and fascinating in their own right, but astronomers can use their predictable rotation for exploring the cosmos in a series of amazing ways. We can detect gravitational waves, navigate the solar system, test general relativity, and find exoplanets. So before we talk about how we can do the science with pulsars, we should probably get to what are pulsars, although, you know, we did a whole episode, so go listen to that one first.
No, we're going to give you the short version of what pulsars are.
Dr. Pamela Gay:
All right, short version. Take a massive star, something probably more than 10 solar masses in size, let it go through its life. At some point, it runs out of fusible materials in its core.
When this happens, core collapses. Core is massive enough that the electrons and protons cannot hold each other apart. They combine, they become neutrons.
We are left with a core of neutrons, a supernova explosion pushes all the outer layers of the star out wherever they want to go. Crab Nebula is a great one to go look at. Take a look at that.
And when these things are young, they are fast rotating, they have powerful magnetic fields. The magnetic fields are not perfectly aligned with the rotational axis. So what you end up with is, as it goes round and round, the pole of the two poles actually of the pulsar go flashing by like a lighthouse.
And it is the material coming out of the poles of the magnetic field that we see as pulses. These are super easy to find in radio and they get their name because they're literally going beep, beep, beep, beep, beep in radio, except sometimes in milliseconds.
Fraser Cain:
Yeah, but weren't they originally designated as like LGMs or was that, yeah, little green men, the first pulsars were found, people thought, are these aliens trying to communicate with us?
Dr. Pamela Gay:
So Jocelyn Bell Burnell discovered these initially and it was part of her dissertation work. She did the engineering of the system. There is a fabulous recording of her with her British accent, her advisor with his Texas accent when they made this discovery.
And they didn't think it was a little green men, they just didn't know what the heck it was at that time. And it eventually led to this revolution in how we understand the magnetic fields associated with these extremely dense little objects.
Fraser Cain:
So before we get on to how we can use your science, you sort of made a bunch of comments and I wanted to sort of get to the whys of these things. So they spin rapidly, why?
Dr. Pamela Gay:
You take roughly more than two solar masses of material that was fairly big, you collapse it down to something roughly the diameter of Manhattan Island. And it is like an ice skater with arms the width of our planet pulling them in around her body. And that body then shrinks until it's the size of like spaghetti.
And so it's zipping around really, really fast because conservation of angular momentum.
Fraser Cain:
They generate powerful magnetic fields, why?
Dr. Pamela Gay:
So they have charged material inside of them. And charged material that is rotating generates magnetic fields. It's not entirely clear how you end up with the rotational axis and the magnetic field axis.
Fraser Cain:
That was my next why.
Dr. Pamela Gay:
Yeah, yeah. I'm not going to try and answer that. There are people who study magnetohydrodynamics, which is fun to say, less fun to calculate.
Those people, they're working on it, they're working on it.
Fraser Cain:
And so imagine this thing is spinning like a little sphere really fast. And when I say fast, like 700 times a second. Like it's crazy how fast these things are spinning.
Spinning really fast. And then there is this magnetic field beams coming off of this thing that is also rotating aligned with the axis of rotation that is sweeping past you like cones, as you said, like a lighthouse that you can then use. So they are wondrous and can fill a lifetime's worth of science just to study them.
But now we can use them for scientific experiments. So then how accurate are these things? Why can we use them for making these kinds of measurements?
Dr. Pamela Gay:
If you put a atomic clock on a shelf next to a receiver for a radio, a radio telescope receiver pointed at a pulsar, the pulses, except for the rare instances where these things glitch because the magnetic field to rearrange themselves, ignoring the occasional glitch, the overall accuracy of a pulsar is better than the atomic clock with the cesium oscillations. That's crazy. Uh-huh.
Fraser Cain:
Yeah. So, so you don't even need atomic clocks. You just need pulsars.
Dr. Pamela Gay:
Exactly. And, and this is what makes them so interesting for so many different kinds of science. And because they're doing their thing in the radio, we can look through a whole lot of gas and dust and see them even when we can't see them.
Fraser Cain:
Right. So then how do we use them as instruments to, to measure? What is the kind of the core physics phenomenon that, that these all rely on?
I'm assuming like the movement of the pulsar in some way.
Dr. Pamela Gay:
It's the Doppler shifting. So when you have this fast rotating object that is ticking like a clock, when it's moving away from you, each pulse has to travel a little bit further than the one before it. So the pulses appear to spread out.
When it's moving towards you, each pulse doesn't have to travel as far. So they're compressed, they're blue shifted. This change in the timing allows us to very, very precisely get a handle on changes in their motion.
This is, is actually something where my senior year of high school, where the being the nerd that I am, I was working at Haystack Observatory. My advisor came running into the computer next to the laser printer, which was where I worked, full ozone unto me. He came running in, closed the door and he's like, okay.
And he just proceeded to download into my brain the discovery of a pulsar planet that was actually real.
Fraser Cain:
- Yeah.
Dr. Pamela Gay:
And, and originally there'd been one that was found earlier that they forgot to correct for the earth's motion. So they ended up discovering a planet that weirdly had the same period as the earth does. And then people realized, oh, we screwed up.
The second time, the second time they did everything correctly and it worked. And when you find structures around something that has undergone a supernova, that just makes it even cooler because these are literally the remnants of like death star levels of destruction.
Fraser Cain:
And so like physically we've got this pulsar, this dead star, and it has planets and they're not very massive going around it, but the, the gravity of the planets are pulling the pulsar back and forth. And so you're measuring that Doppler shift on the radio waves that are coming to you, allowing you to tease out the masses of the planets that are going around the pulsar. That is, that is really impressive.
And, and it's also very frustrating for me as a science communicator. And I'm sure you go through this as well, which is you say the first planets ever found was in 1995 with the Pegasi, right? And then people go, well, actually the first planets that were ever found were around a pulsar.
And you're like, yes, sorry. So you always have to put in this disclaimer, the first planets ever found orbiting around a sun-like star or a main sequence star was Pegasi blah, blah, blah, right? 51 Pegasi b, but the first planets ever found were orbiting around a pulsar.
And that is just, it's always drives me crazy.
Dr. Pamela Gay:
They just weren't planets in the sense that we're used to, and they weren't orbiting a star in any sense of the word. So a stellar remnant with asteroid like things that came out of a supernova, we just sort of set that on a shelf and go, that's an exception, but yes, it's very, very cool.
Fraser Cain:
And think about the weirdness that it has, whatever it is, like a Mars sized, like several planets orbiting around it. This star exploded and yet it has planets.
Dr. Pamela Gay:
Yes.
Fraser Cain:
It's awesome. Yeah. And yet weirdly, we haven't found many other examples of this, which you would think you would find lots more.
Dr. Pamela Gay:
You would think, but when you start to realize pulsars are very young, they're very hot, but the heat is capable of destroying solid objects very effectively. There was a recent paper, probably six months old now, looking at white dwarfs and their ability to ionize planets. You have to have material that survived the heat, survived the explosion or migrated in the time scales.
It's going to be rare.
Fraser Cain:
Yeah. So that's just one example and I think that's great because it gives you a sort of basic, the tool is always the same, which is that you're calculating that Doppler shift to discover something about the environment that the pulsar is in. So let's pick another one.
Dr. Pamela Gay:
So Joseph Taylor and Russell Hulsa, back in 1974, were studying binary systems containing pulsars and they noticed that one of these systems that was showing the variations indicative of the pulsar being in a binary system and the companion was not visible, was also showing a change in periodicity over time that appeared to be radiation of gravitational energy, which is something at that point was strictly theoretical.
Fraser Cain:
Predicted by Einstein.
Dr. Pamela Gay:
Predicted by Einstein, not yet seen, but ultimately what they were able to figure out was pulsar B1913 plus 16 was in orbit with a stellar mass black hole and over time these two objects were radiating away gravitational energy and Taylor and Hulsa went on to get the Nobel Prize in 1993 for work that Hulsa was just a graduate student while doing and I just love that they went, they proved something and it literally took a generation before everyone was like, okay, we got you, we agree, this was actually, here's the Nobel Prize.
It was just such cool work and we found other systems like that since then and this was the first evidence that gravitational waves should be out there. And what I love is this Nobel Prize was given out at the same time that so much energy was going into building LIGO so that we could start directly measuring gravitational waves instead of just seeing them from how their energy changed orbits.
Fraser Cain:
So it's almost the same thing, which is that whenever I say, oh yeah, the first detection of gravitational waves was from LIGO in 2015 and people go, well, actually, pulsar, no, pulsars again, right? Actually the first gravitational waves were confirmed by pulsars because we detected the loss of energy, the loss of orbital momentum caused by the pulsar and its companion bleeding off energy into gravitational waves. Okay, yeah, you're right, you're right.
So now I have to always disclaim that the first directly detected gravitational waves came from LIGO, but the first gravitational waves, yeah, found by pulsars, incredible. What else you got?
Dr. Pamela Gay:
So there's the classic idea that at some point in the future, we're going to need to be able to navigate through the galaxy, at least one hopes. And one way to do this is to have essentially radio eyes on the sky that monitor in all directions where the pulsars are. And what is, so you look for the pulsars, you measure the periodicity and you measure how those shift and the grid on the sky three-dimensionally of where pulsars are located is set by where these things are in their own orbits around the galaxy.
The rate that they appear will be blue-shifted or red-shifted by the navigator's motion through the galaxy. And this is a way to get a unique solution to how you're moving and where you're spatially located.
Fraser Cain:
And this is not just theoretical, this has been demonstrated. So there is a pulsar detection system on the International Space Station, and they were able to use its ability to track its position based on pulsars to within tens of meters. So it was able to accurately measure its movement in a way that is independent from the other methods that are used to navigate the International Space Station.
That if you were dropped randomly in the Milky Way, if you found a bunch of pulsars, you would be able to find out where you are. If you were moving, you would be able to know the direction that you're moving purely based on the blue-shift, red-shift from the various pulsars. On the, is it the Voyagers or is it the Pioneers?
But there is a plaque, I feel like it's on the Voyagers. It's on the Voyagers. It's on the Voyagers that shows where the solar system is based on known pulsars in various directions.
And so any alien civilization can come and destroy planet Earth and steal our resources because we gave them a map to our home, thanks to pulsars. And so there are people that are working on these essentially navigation boxes that you will put on all spacecraft that will then just use pulsars to know where they are. And so the spacecraft could go to sleep, wake up, look around, measure all the pulsars around it and go, oh, I know where I am.
To a level of accuracy that it can make deorbit burns and do the kinds of spacecraft maneuvering that would be required without depending on communication from Earth. Thanks pulsars. Okay.
Let's talk, let's talk more about gravitational waves. I was hoping that was where you would go. And we'll talk about the background gravitational waves.
Dr. Pamela Gay:
So once you understand that the timing of these things can be affected by any change in distance and you start realizing monitoring these things over time is actually super useful. You can start to imagine, all right, we're monitoring pulsars in every direction and large enough gravitational waves moving through the universe, we'll be able to stretch and compact the distance between us and pulsars in a way that we will see as timing changes and we'll see those timing changes as the gravitational waves sweep through the, sweeps through the galaxy. Now I'm going to give you a very simplified picture here.
So you can imagine in the perfect setup, there is a massive gravitational wave moving through the Milky Way galaxy and we initially see changes in stars in that direction at great distance and then we see it from closer and closer and then we start seeing it from behind us. And so you literally see these timing differences propagate across the galaxy in a way that allows you to say, aha, so gravitational wave came from over there and it's headed in that direction. Now the problem is our universe is vast, it has interesting stuff going on all the time in all the different directions and so what we see instead is the pulsar timing array is out there looking in all directions, looking at the noise in the pulsar timing and using that noise to say, is this consistent with gravitational waves wrecking very, very minor havoc on the distances to these pulsars?
Fraser Cain:
Right, right. So it's, you know, the description is always like, it's buoys floating on the ocean and yes, if a tsunami went by, then the buoy would probably rise up and fall back down. But instead you're just watching the buoy from all of the collective wave action of everything that's going around it and that statistically over 15 years looking at dozens of pulsars, astronomers have confirmed what?
Dr. Pamela Gay:
Noise is consistent with gravitational wave detections.
Fraser Cain:
Right, from merging supermassive black holes. Yes, which is awesome. Awesome, yeah.
That we know that supermassive black holes are merging, we can't detect them directly, it's beyond the capability of LIGO and other ground-based detectors. It's the wrong scale. But in aggregate, their mergers are sending out gravitational waves that are causing the pulsars to bob around in a way that tells you that this is happening.
There's a paper that just came out yesterday. Oh, I haven't seen it yet. That we're reporting on.
Yeah, so astronomers attempted to confirm if they could detect any single gravitational wave event from supermassive black holes and they failed. But as always, when you fail, you set constraints. So the longer the pulsar timing array operates for 25 years, 50 years, that we may get these individual events starting to get teased out if the event is strong enough, close enough, significant enough, that we may actually eventually get individual colliding supermassive black holes from the pulsar timing array.
But so far, it hasn't happened. You only get it in aggregate. You don't get it as a specific event.
Still, amazing. Amazing.
Dr. Pamela Gay:
I think we have one last thing to bring up.
Fraser Cain:
Right.
Dr. Pamela Gay:
And that is a recent candidate discovery from the Breakthrough folks where they were out there looking for little green men. So this was research that was designed specifically to look for civilization's technosignatures and they were looking towards the center of our galaxy. So this is Breakthrough Listen.
They're looking within 1.4 arc minutes of the galactic core. And this is a hairy region to look at because there's our own supermassive black holes magnetic field that is making a mess of any radio signals that are coming from that direction. They found within that region in one hour of data a candidate pulsar that if confirmed could be down in the center of our galaxy where it would be under the influence of all the different things in the center of the galaxy.
And it could show relativistic effects in how its timing changes. Now, there's a whole lot of caveats from what I just said because while they saw it in one hour of data, they weren't able to confirm it in other data sets. They're going to go back.
They're going to take more data. And the concern I saw expressed in the paper was there is the potential that interactions with other local magnetic fields could cause this thing to go in and out of view, which is just a big furry mess to imagine. Again, magnetohydrodynamics is fun to say, hard to do.
Yeah, hard to do. And so, it's unclear if this is real or not, but we can use pulsars to measure relativistic situations, to measure motions in small places, to do all sorts of cool physics because they are literally sitting there as metronomes demanding our attention in ways that allow us to measure their motion extraordinarily precisely.
Fraser Cain:
So, you actually did leave out a bunch. It's true. Which just shows how useful pulsars are.
So, I want to give just a few more quickly. So, one is just the analysis of pulsars themselves. So, we've learned recently that pulsars do have these glitches.
You mentioned ignoring the glitches. Well, the glitches are important. And that they tell us just by measuring the spin rate of the pulsars that you can detect when they go through these glitches.
And then it appears that even though they are balls of compressed material that seems like it can go no further, they actually can and that they crunch and crumble and have little mini earthquakes on them, which is very impressive. They are the best way to measure the mass of a star because when you've got a star and a pulsar that are in orbit around each other, that this atomic clock level precision of the measurement of the orbit gives you a precise measurement of the mass of the star that the pulsar is orbiting. And there's no better way to do that.
Dr. Pamela Gay:
It's a standard homework assignment.
Fraser Cain:
Yeah, yeah, there you go. Yeah, exactly. You've got a pulsar, here's the orbit, here's the change in the Doppler shift, tell me the mass of its companion star.
And in fact, telling the mass of stars is actually really hard. And so, every now and then when you get a pulsar in orbit around one of these things, you have this beautiful gift from the cosmos. And then the other thing is just that the radio waves that are coming off of the pulsars are going through whatever is the material that is between us and them.
And so, they've been used to probe the interstellar medium, the intergalactic medium, be able to, as you mentioned, the detection of a pulsar close to the galactic center. These are places that are hard to observe visually, but radio waves can pierce through them. And that the more of this material that the radio waves are going through, you get this probe of the intervening material and pulsars are very useful for this.
So, pulsars are just this incredible gift from the cosmos for astronomers to learn more about the cosmos. And we are so grateful.
Dr. Pamela Gay:
And conservation of angular momentum is why we have them.
Fraser Cain:
Yeah.
Dr. Pamela Gay:
And they're slowing down over time. And that allows us to like get at evolution. And yeah, they're just cool because they're weird, but they're precise in their weirdness.
Fraser Cain:
Yes.
Dr. Pamela Gay:
So, more of that, please.
Fraser Cain:
Yes.
Dr. Pamela Gay:
More of that.
Fraser Cain:
Yep. All right. Thanks, Bella.
Dr. Pamela Gay:
Thank you, Fraser. And thank you so much to all of our patrons out there on patreon.com slash astronomycast. This week, we would like to thank by name, a bulky 60, Adrian Bradley, Alex Cohen, Andrea Segel, Andy Moore, Antonio Reese, Arthur Buttenbrook, Astro Zatz, Beat Fares, Benjamin Mueller, Bob Blanswitz, Brad W.
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Fraser Cain:
Thanks everyone, and we will see you next week. Bye.
Dr. Pamela Gay:
Bye everyone
Live Show
Modern astronomy has found that the Universe can surprise us. Here’s one which astronomers have called Luminous Fast Blue Optical Transients. They’re kinda like supernovas, they’re kind of like gamma ray bursts, but they’re not like them. So what are they? In the distant Universe, are blue light flashes, bright and hard to understand. These objects, uncreatively named "Luminous Fast Blue Optical Transients," are just the kind of puzzle astronomers love. In this episode, we look at their discovery and our current understanding of what they might be.
Show Notes* Discovery of a new class of transients: Luminous Fast Blue Optical Transients (LFBOTs) * First major example: AT2018COW (“The Cow”) * Extreme brightness: up to 10⁴⁴ ergs/sec, rivaling the most energetic explosions * Brightest recent case: AT2024WPP (“The Wasp”) * How LFBOTs differ from supernovae and gamma-ray bursts * Role of the Zwicky Transient Facility (ZTF) in discovering fast transients * Possible origins: + Black holes consuming Wolf-Rayet stars + Tidal Disruption Events (TDEs) + Stellar-mass black hole interactions * Connection to gamma-ray burst classifications (short vs long) * Binary star systems and extreme stellar evolution pathways * Impact of black hole activity on surrounding star and planet formation * Need for future UV and next-generation observatories * Growing statistical samples to better understand black hole feeding behavior * Humorous nickname proposal: “Blooper Novas” * Patron appreciation and episode close
TranscriptFraser Cain:
Astronomy Cast, Episode 782 Luminous, Fast, Blue Optical Transition. Welcome to Astronomy Cast, our weekly facts-based journey through the Cosmos, where we help you understand not only what we know, but how we know what we know. I'm Fraser Cain, I'm the publisher of Universe Today.
With me, as always, is Dr. Pamela Gay, a Senior Scientist for the Planetary Science Institute, and the Director of CosmoQuest. Hey Pamela, how are you doing?
Dr. Pamela Gay:
We have our first sign of spring, the snowballs, the little tiny white bulbs have come up. They have bloomed. Mine haven't.
They've come through the snow, which is what they're supposed to do. And so we've had our first bulbs of spring.
Fraser Cain:
Yeah, we haven't had those yet. All of my bulbs are sort of peeking through the ground now, through the ground layer, but no flowers yet. But I'm probably just a week or two away.
And flowers on my trees, on my cherry trees. So I'm looking forward to that. Modern astronomy has found new ways that the Universe can surprise us.
Here's one which astronomers have called Luminous Fast Blue Optical Transits. They're kind of like supernova, they're kind of like gamma ray bursts, but they're not like them. So what are they?
So I guess, set the stage, when and how did astronomers, it started to dawn on them there was an entirely new class of objects out there in the Universe. And we need to also come up with an acronym or a better name for this, but maybe we'll do that later.
Dr. Pamela Gay:
All right. So back in 2018, folks looking through ATLAS and Hong Kong Observatory data followed up on a transient from the Zwicky Transient Facility. So it was found in this other data set.
It was backtracked to being in the Zwicky data set. And it was cataloged, I kid you not, as AT2018COW.
Fraser Cain:
The cow.
Dr. Pamela Gay:
The cow.
Fraser Cain:
Right. It sounds like a call sign for a radio station.
Dr. Pamela Gay:
And I just love the fact that this stuff just serendipitously happens because of how we name these transients. We just cycle through the alphabet over and over and over. And it turns out the Zwicky Transient Facility is out there doing an obscene amount of transient discoveries that is not getting discussed.
They are able to prototype a whole lot of the data pipelines that are going to be used for the Rubin Observatory using the Zwicky Transient Facility because it is finding supernova after supernova, moving object after moving object, weirdo blue thing in the sky after weirdo blue thing in the sky. And the cow.
Fraser Cain:
Yes.
Dr. Pamela Gay:
The cow.
Fraser Cain:
The cow.
Dr. Pamela Gay:
The cow.
Fraser Cain:
2018, the cow. Yeah.
Dr. Pamela Gay:
It was an object that put out more light than any supernova thus far seen, which was not on anyone's bingo card.
Fraser Cain:
That's impressive.
Dr. Pamela Gay:
Yeah. Yeah. 10 to the 44 ergs per second.
Fraser Cain:Now that's how you describe a lot of energy. You got to stay in ergs. Now we're talking.
It's true. It's true.
Dr. Pamela Gay:And so there was a whole lot of what on earth could cause this confusion and hopes that there would be more. And the sky did not disappoint. And for the first time in my career, neither did the names.
I'm going to be stupidly excited about the names of these things because astronomers generically are really, really bad at naming things. But the next one that was found was ZTF, Zwicky Transient Facility, 18 ABV, the ABV is very boring, KWLA, which became koala. Right.
So, so this one was also in 2018 and it was documented to reach 40,000 degrees Kelvin. They didn't have a clear distance to it, so they didn't initially have clear luminosity to it. They just knew it was really, really hot, really hot.
Fraser Cain:And since then, I mean, we have found probably about 10 of these objects and, and clearly some the, the astronomers that studies are delighted because as you said, they're giving them silly names based on a kind of a rough correlation of what the gobbledygook alphanumeric code ends up being close to those animals.
Dr. Pamela Gay:
So ZTF 20 ACIG MEL, so there is a C and there is an MEL, it became the camel, then we have 2023 FHN became either the finch or the fawn. And the most important one, I think for today's discussion is AT 2024 WPP, the wasp, right?
Fraser Cain:
And this is the brightest one that has ever been seen.
Dr. Pamela Gay:
Yeah. Yes.
Fraser Cain:
Okay. So, so that's great. And so give us a sense of the characteristics of the explosion.
What makes it so much different than say a supernova or a gamma ray burst?
Dr. Pamela Gay:
So this is something that for just a matter of weeks, peaks in brightness, extremely in the blue, extremely, extremely in the blue. So we're talking super hot, and it's also putting out an indescribably large amount of energy. Like this thing is common for you.
It is the wasp, the most powerful one, put out the equivalent of take 10% of the sun's mass and just turn it into energy. And that's how much energy it put out.
Fraser Cain:
Wow. Like E equals MC squared, just convert that matter into energy.
Dr. Pamela Gay:
Just straight to energy. It's not messing around. It's just like, I'm here, I'm blue, I am hot.
I have energy.
Fraser Cain:
But when we think about say gamma ray bursts, right, we have the short and long gamma ray bursts where it's sort of like the two second mark. If it's less than two seconds, that's a short gamma ray burst. And those appear to be colliding neutron stars.
If it's long, then it's a long gamma ray burst. And those are hundreds of seconds. Yeah.
And they can be much, two seconds or longer, but yeah, it can be hundreds of seconds. And that is a core collapse supernova. And that's different from the gamma ray bursts.
Yeah. These are like 20 days. Right.
And, and, and like, why do astronomers think that they are not either gamma ray bursts or supernova?
Dr. Pamela Gay:
So the, the gamma ray bursts, they, they just don't fit with any of the gamma ray bursts that we're seeing. They're, they're not showing up in Fermi data the same way that gamma ray bursts do. And if you don't look and smell like a gamma ray burst, you probably aren't a gamma ray burst.
But then the amount of energy that's coming out of them is just so much greater than what we've seen from supernovae that initially they were like thinking, maybe there's some kind of super luminous supernovae. These are some kind of supernovae we haven't seen before. And so people went with that theory as one possibility.
Then there was the, maybe this is something that's getting shredded, something that's getting destroyed, something that, that's getting converted from mass to energy and went down that rabbit hole as well. So there are all these options and we just needed more data.
Fraser Cain:
Right. And, and we have more data. So you know, we did a flurry of reporting on this at Universe Today in the last couple of months or so, um, where it looks like astronomers think they're starting to settle in on an explanation.
Dr. Pamela Gay:
It's true.
Fraser Cain:
And, and it's really cool because again, remember you're a budding super villain, Pamela.
Dr. Pamela Gay:
I know.
Fraser Cain:
So when you say something is really cool, other people should say, is this causing the entire destruction of a large volume of space? Yes. Yes.
Dr. Pamela Gay:I, yeah.
Fraser Cain:
Yeah. Yeah. Just remember, Pamela is a super villain, which is something that's cool.
You should be afraid. All right. She loves, she loves super volcanoes.
This is, this is what we're talking about here. But yes, it is super cool.
Dr. Pamela Gay:
All right. So sometimes one answer can encompass a spectrum of behaviors. And so in this case, it's looking like what's happening is you have stellar mass black holes for some value of stellar mass that are consuming gas, consuming stars, shredding neighbors with the wasp, the most powerful of these thus far seen, probably being a roughly 10 solar mass black hole being orbited by a Wolf Ray A star.
So something young that when these two stars were on, when they were zero age main sequence stars, the one that's currently a 10 solar mass black hole was the bigger of the two stars. The Wolf Ray A was the smaller of the two stars. And had it been allowed to live, they would have ended up being a binary black hole system someday.
However, instead, the Wolf Ray A star got too close to the black hole. There's lots of different things that can cause stars to migrate together. And it appears that a chunk of material was torn off the Wolf Ray A star as it was disrupted.
And that chunk of material, again, roughly 10% the mass of the sun. It just became energy.
Fraser Cain:
Yeah.
Dr. Pamela Gay:
As you do. As you do.
Fraser Cain:
Right. Right. So, so one thing, just to clarify, you said Wolf Ray A stars are young.
They are, they're an evolved form of stars. They're, they're so, so it's a star where they've gone through the main sequence phase. Now they've sort of blown away a lot of their outer layers, but they're, but they're massive and, and going to explode.
Dr. Pamela Gay:
And this is one of those times where adjectives are, are not what we should be using because a Wolf Ray A star has an age that's still measured using millions and billions. And so in my brain, it never becomes old. It dies young.
Fraser Cain:
Dies young. Yeah.
Dr. Pamela Gay:
And, and so, so basically they become angry teenagers and die.
Fraser Cain:
Yeah. Now again, super villain, Pamela just described that event in very clinical terms. So allow me to sort of describe the true horror of what just happened here.
You've got a black hole, 10 times the mass of sun orbited by another massive, very massive star. The star got too close and the black hole tore off. It disrupted it.
A huge chunk of that star and just nommed it away, causing this extremely bright flash. And you got this, you know, this bright blue ultraviolet flash coming from this, this object. And it appears that these, these blue optical transits are caused when stars are dismembered by black holes.
Dr. Pamela Gay:
And, and there's still the potential that this could be clouds of material getting consumed. That is not eliminated. These things come in a variety of brightnesses.
They behave slightly differently. Not all of them are going to be Wolf Ray A stars getting disrupted, which is magnificent when it does occur. But we can imagine, we've, we've lately, there has been this amazing rash of really weird stuff getting found.
So there was recently a star found that had what appears to be two planets collided and formed a giant disc around a settling together, super Jupiter. And we've seen before with, I think it was Epsilon and Regi where you have a binary system that has a protoplanetary disc around the companion star. So we can imagine seeing these kinds of luminous fast blue optical transients in systems where there there's material that hasn't formed into a star yet.
What we know for certain is these things appear to consistently occur in galaxies with a large amount of star formation going on in galaxies where you expect to see massive stars still living and breathing until they get shredded by their neighbor. And it's these kinds of systems that allow stars with ages in the millions instead of the billions to exist where we're seeing these events occurring. So again, it's massive stars getting disrupted, but there's the potential also for neighboring stars to lose their planetary discs as they get eaten before life can form.
Fraser Cain:
And it's interesting to sort of see, like we have seen various flavors of black holes consuming stars across the universe, but generally it's in the, a supermassive black hole just tore a star apart and the supermassive black hole already has accretion disc around it. And this was a minor addition to the overall luminosity that is coming from the black hole. Or we get this situation, we talked about this I think last week or a couple of weeks ago, that you can have black holes or even stars passing through the accretion disc around a supermassive black hole and then you get that flash.
But this is much more, you know, that's like a giant stepping on a bug. This is sort of, I don't know, to use the analogy, like a tiger taking down something that's, you know, bigger than it, an elephant, right?
Dr. Pamela Gay:
I mean, the thing about this is this had the potential to be a black hole, black hole system that we would later see merge, not us, we'll be dead. Someone would eventually see merge with gravitational waves being released into a larger black hole. But this was literally a tensile or mass black hole saying, nope, you don't get to be like me.
You shall be my dinner.
Fraser Cain:
Right. And so is it doomed? Like there was like now it's just, it's going to be meal after meal after meal until it's gone into the accretion disc and then into the black hole and it'll never get that chance to detonate on its own as a supernova.
Dr. Pamela Gay:
Exactly.
Fraser Cain:
Wow.
Dr. Pamela Gay:
Yeah.
Fraser Cain:
Yeah. Awesome. Again.
I mean, although I think that works, you know, it was awesome in that it is feel it will fill you with awe to watch it. Yes. To Slackjaw.
So first we got to deal with one other issue here, which is the name.
Dr. Pamela Gay:
Yeah. It's terrible.
Fraser Cain:
It's terrible. It's luminous. I don't even remember.
Hold on.
Dr. Pamela Gay:
Look this up. Okay.
Fraser Cain:
Okay. But the acronym is no better. And astronomers genuinely are usually pretty good at this.
So it's LFBOT. LFBOT. It's terrible.
It's terrible. They named the objects well. So I asked my audience to come up with some better names and my favorite so far is a blooper nova.
What do you think?
Dr. Pamela Gay:
Yes. Yes, please.
Fraser Cain:
Yes. All right. So astronomers, if you're listening, that is the name.
They're not LFBOTs, right? They are blooper novas. So then what does the future hold for the system then?
Dr. Pamela Gay:
So this particular system, I mean, it's not possible to say with any certainty exactly how things die. We're not there as a profession yet. But over timescales, I'm not going to guess, chunks are going to get consumed.
There will be additional luminous blue goodness as this disrupted object forms potentially a disk as it potentially has jets. We've seen jets in other situations. It's the case of it's dying.
It has to shed its angular momentum. There's going to end up being a disk at some point. Disks like to build magnetic fields.
Those like to build jets. It's going to do the black holes eat things and it looks the same no matter what the scale is. But what's cool is we're entering an age where we just started finding these less than 10 years ago and we're able to find it because of the Zwicky transient facility.
It's a fairly large scope. It's out there just going bang, bang, bang, looking at the sky, looking for things that twinkle, flit, flare, move in the night.
Fraser Cain:
Oh, I wonder if there's like another observatory that's just about to come online that's going to do that.
Dr. Pamela Gay:
Southern hemisphere maybe? So that new pipeline that is going to be able to see even more starbursting galaxies, which are much more common in the early universe. You get that bigger mirror.
You're going to be able to see things, resolve things further out. You're going to be able to see more of these in its great depths. And so I am hoping that the things that we've started to learn exist, thanks to the Zwicky transient facility.
We're going to get statistically significant samples of that explore the whole, here's the span of luminosities. Here is the span of periodicities. Here is one that's recurring.
Here is five that have jets that as we find more and more of them, we're going to start to understand all the ways that black holes eat their neighbors. And we're used to seeing this kind of consumption and cataclysmic variables, which is on our list of shows we need to do. But we needed to do this show first because there is an object called the cow.
Right. And that is excellent.
Fraser Cain:
Yeah. Yeah. I mean, you mentioned Vera Rubin and there's actually a couple of ultraviolet observatories that are going to be coming online.
And this is a tricky one because the wavelengths that you need to be able to detect this, you need to be in space. You need a space telescope. And that there are a couple of ultraviolet observatories in the works right now that should get us to this place where we can start to observe these on a regular basis.
Do fall on observations and cross compare with what Vera Rubin is finding. And it's expected that we should get dozens of these every year. And then you can really break them down and say, okay, you know, these are the ones where it's a Wolf-Reye star, but maybe these are the ones where it's a regular star or a main sequence star, or it just ate a red dwarf or whatever that, that, that, that, you know, we know that massive stars tend to come in multiple star systems.
And so then what is the trajectory of those star systems? Do you get two black holes orbiting each other, which then merge, do you get neutron stars that merge? Do you get a white, two white dwarfs that eventually merge?
Do you get white dwarfs that consume off of a companion star and then you get a type one a supernova? Do you get a black hole that consumes its companion or do you just get two stars that are far away and they just never do anything mean to each other at all?
Dr. Pamela Gay:
So the thing that I'm hoping that we see is we, we have hints that hypernova that generate long duration gamma ray bursts are potentially a binary system where the massive star goes supernova onto a compact neighbor that has given it extra angular momentum. And so we're going to be seeing potentially systems that that compact neighbor is not just a neutron star, it's a black hole. And as you go supernova, that material goes and gets eaten.
And, and, and these are low probability objects. The most massive objects are the most rare. The initial mass function of stars is like not very many super bright ones, lots and lots and lots and lots of these really faint ones.
And then we're just left with a universe of uninteresting little tiny red stars that like to bake their baby planets. The more sample size we have, the higher the likelihood we're going to start seeing these long duration gamma ray bursts to understand what's going on and start seeing them in more and more kinds of pairs. And it's just awesome.
[Speaker 5]
Yep. Yep.
Fraser Cain:
I mean, and, and that's the part that I really love. I mean, you know, to go down a totally different rabbit hole, we're sort of moving into the same regime with exoplanets and their atmospheres. I mean, you know, we only, we know of say 6,000 exoplanets, but we only have a few dozen that their atmospheres have even been imaged, none that are earth-sized, you know, around red dwarfs or around sun-like stars.
And so we don't know what's normal yet. We don't know what is the, how these things evolve. And when new telescopes come online, they will get these larger data and eventually we will be, you know, we will know tens of thousands, hundreds of thousands, millions of planetary systems, and we will understand in this very rich way.
And then we will be able to do the same for the future of star systems that we can look out and have enough of the universe in our minds at one time that we will understand how things work, how things play out, what the future evolution looks like, what the past looks like. It's a, it's a very cool direction that we're heading in. And a lot of these big tools, especially Vera Rubin are going to get us huge steps forward.
So any day now. So just one last reminder, everybody, blooper novas.
Dr. Pamela Gay:
Okay. We seriously need to figure out who to write to because that is excellent.
Fraser Cain: Yeah. But we just do, you don't write to anybody. You just start saying the word until it sticks.
Dr. Pamela Gay:
I like that.
Fraser Cain:
All right. Thanks, Pamela.
Dr. Pamela Gay:
Thank you, Fraser. And thank you so much to everyone out on Patreon who is supporting us at patreon.com slash astronomy cast this week. We would like to thank the following $10 a month and up patrons, Adam and he's Brown, Alex rain, Andrew palestra and to sore Astro Bob, Bart Flaherty, Benjamin Davies, Bob Zatsky, Bresnik, Brian Cagle, Bruce Amazine, Kami Rassian, Cody Rose, Dale Alexander, David, David Green, D's Astrina, Dr. Jeff Collins, Elliot Walker, evil Melky, Felix Gute, Frank Stewart, galactic president, scooper star McScoops, a lot, Glenn Phelps, Gordon Dewis, Gregory Singleton, Helga Bjorkog, James Signovich, Jason Kwong, Jeff Wilson, Jim Schooler, Joe Holstein, John Drake, John phase, Gordon, Jordan Turner, Justin s, Katie and Ulysses, Kim Baron, Kinsaia, Penflanko, Laura Kettleson, Lou Zealand, Mark Masa, Haleu, Matthew Horstman, Michael Prashada, Michael Regan, Mike Hosey, Nick Boyd, Papa hot dog, Paul L Hayden, Philip Grand, Randall, R3, Robert Cordova, Ron Thorson, Ruzzard with a Z, Sage Sinfin, Chersem, Scott Briggs, Sergei Manilov, Slug, Stephen Miller, The Big Squish Squash, Thomas Gazzetta, Time Lord Iroh, Tushar Nakini, Wanderer M101, William Andrews. Thank you all so very much.
Fraser Cain:
All right. Thanks, everyone. And we will see you next week.
Dr. Pamela Gay:
Bye-bye.
Live Show
There are stellar-mass and supermassive black holes. But very little evidence of anything in between. Where are all the intermediate-mass black holes that should be the building blocks of the biggest ones? Actually, the science has been accelerating rapidly and we now know of hundreds of them. The question marks in our understanding are slowly getting replaced with data. Let's review what we now know about intermediate mass black holes and their origins.
Show Notes* Funding Concerns * Intermediate-Mass Black Holes * Stellar-Mass Black Hole Mass * Black Hole Formation Gaps * Stellar Mass Black Hole Formation * Supermassive Black Hole Mass * Missing Intermediate-Mass Black Holes * Black Hole Discovery Timeline * LIGO’s Contribution * Intermediate Mass Black Holes * Globular Clusters as Potential Hosts * Intermediate-Mass Black Hole Evidence * Globular Cluster Formation * DESI’s Role * Dwarf Galaxy Discovery * Active Galactic Nuclei in Dwarf Galaxies * Intermediate Mass Black Holes * Early Universe Complexity * Theoretical Challenges * Formation of Massive Objects * Intermediate Mass Black Holes in Dwarf Galaxies * Hypervelocity Star Ejection * Formation of Mini Quasars * Dwarf Galaxy Characteristics * Intermediate-Mass Black Hole Evidence
TranscriptFraser Cain: It's the 365 Days of Astronomy podcast, coming in three, two, one. AstronomyCast, Episode 755, Intermediate Mass Black Holes. Welcome to AstronomyCast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know.
I'm Fraser Cain. I'm the publisher of Universe Today. With me, as always, is Dr. Pamela Gay, a Senior Scientist for the Planetary Science Institute and the Director of CosmoQuest. Hey Pamela, how are you doing?
Dr. Pamela Gay: I am happy to be doing AstronomyCast.
Fraser Cain: As opposed to all of the other stuff that's going on right now?
Dr. Pamela Gay: Yeah. Yeah. It's one of these things where we try not to get too political on here, but what is happening to funding the science in the United States?
Yeah.
Fraser Cain: Yeah. I mean, for a lot of people who watch Universe Today, and I talk to the people, the fans and stuff, and they're like, oh, I really like that you're not very political, Fraser. But that's about it.
I'm going to have to report on a 25% proposed cut to NASA, cancellation of most of everybody's favorite science missions, the probable cancellation of the Artemis mission, Moon plans, the 54% cut to the National Science Foundation. That includes, like, we don't know what the implications are going to be, but you know, things like, I don't know, Vera Rubin Telescope. You know, there are all these incredible science projects that are in the works.
And then you layer on top of that, the cuts to the universities, you layer on top of that, the cuts to, you know, all of the DEI cancellations and cuts that are going on, as well as all of the people to administer this, as well as all the holds and freezes. Science is just going to lock up in the US at this point. That is my objective, non-political take on what's about to happen.
And so it could be complicated. And you know, science, NASA specifically, has sort of dodged a whole bunch of bullets that have gone by so far. And now we've seen the budget request.
And so we haven't seen what the actual Congress response is going to be, whether they're going to just rubber stamp it or whether they're going to push back and come up with their own version of the budget. So that is, that's sort of like the final line of defense.
Dr. Pamela Gay: Yeah. And one of the things that I've realized talking to people is a lot of folks really don't understand how scientists get their salaries and the fact that the vast majority of us are funded entirely through things that can be routed back to the government. And this is something that's going to cause a significant proportion of scientists to leave the field entirely.
Fraser Cain: Yeah, yeah. I mean, I'm already talking with people who are saying, you know, I was going to be going to university in the US because it's the best and now I'm not going to. Right?
So you're going to have this brain drain of people not, you're going to have this, this, people are going to be avoiding the US science. And then on top of that, people who are already scientists are going to find programs at other universities that are going to give a more stable funding environment. You're going to see large, you know, very established teams of researchers have been working in, you know, very productive, either fragmenting because of lack of funding or rebuilding their operations in some other camp, you know, other nation like Canada.
Like, like we're unfortunately for the US going to be the, uh, the inheritors of all of this chaos. We're going to have, uh, you know, a lot of incredible researchers are going to come and come work in Canada because, you know, we don't have any of these cuts. So anyway, let's, let's move on.
Uh, you know, I think this is going to be an episode like once the dust has settled and once we, once everything is kind of verified, like right now, everything is still kind of in, in the mix, but once everything is verified, I think we will do an episode which we'll just sort of say, you know, here's everything that happened and try to give you the most, uh, unbiased, but brutal, uh, reckoning of what has actually happened. So, so stay tuned for that in, in, in some number of weeks or months.
Dr. Pamela Gay: But if you want to find out how scientists are actually paid, go listen to the most recent episode of EVSN at EVSN.TV. Oh, great.
Fraser Cain: There you go. There are stellar mass and supermassive black holes, but very little evidence of anything in between. Where are all the intermediate mass black holes that should be the building blocks of the biggest ones?
Actually, the science has been accelerating rapidly and we now know of hundreds of them. So, so let's sort of give people a sense of the, just the gap between them. What is the typical mass of a stellar mass black hole?
Dr. Pamela Gay: So typical mass is a really weird thing to talk about because we are still doing a survey of, of all the stuff that's out there. Like there weren't confirmed black holes until this century and we're only 25 years into this century. So we, we are fairly certain that there's a large number of them that are in the few solar mass to 20-ish solar mass numbers.
Then there are more that are bigger. And then there's another gap and there's more that are even larger. So there's this weird situation where if you have a star that is less than 10 to 20 solar masses, which is a fuzzy number, but mass loss is confusing.
It's going to end up becoming a neutron star and create big nebula, big supernova, lots of mass loss. So it ends up tiny, tiny. If you have bigger than that 10 to 20 solar masses, most likely bigger than 20 solar masses, you end up with a supernova going off that creates a black hole in the center, big normal nebula.
Life is good. You have an object bigger than 50 to a hundred solar masses, most likely 50, and it's going to collapse straight down into a black hole because gravity is like, nope, no supernova for you. But then you get even bigger and you end up with what's called a pair instability where as that object tries to collapse, you end up with positrons and electrons getting formed, vast amounts of energy going off.
And so you end up with a completely different kind of star go boom and another gap in black hole formation.
Fraser Cain: Right. Right.
Dr. Pamela Gay: Because it looks like probably a gamma ray burst, right? Yeah. This is where they're looking at hypernovas and stuff.
Fraser Cain: Yeah. Yeah. And because it's all antimatter and matter in the middle, the whole star is just gone.
Dr. Pamela Gay: So you have these two different gaps and if your star is really big, you don't end up with a black hole and, and at the same time we're finding stuff with LIGO that seems to imply that either they're still forming in those mass gap regions or things that shouldn't have time to merge have merged and, and the universe not matching what we expected will be a theme in this episode.
Fraser Cain: Yeah. Yeah. Okay.
So those are the stellar mass black holes and now let's shift to the supermassive black holes. What kind of mass regime do we see with them?
Dr. Pamela Gay: So, so here we're looking at things that are larger than a hundred thousand solar masses and they go up to millions of solar masses.
Fraser Cain: Billions.
Dr. Pamela Gay: Billions of solar masses. Yeah. Yeah.
And, and so in this case we're looking at a, we, we thought that they probably formed through mergers, but the universe hasn't been around that long. We haven't seen enough merger events. So maybe they form via turbulent infall of matter while galaxies are forming and then you end up with some mergers that get you to the giant ones, but there's a whole lot of confusion there as well.
Fraser Cain: And so then astronomers have always been theorizing that there is, there's gotta be something in between. There's gotta be something like you don't just get these supermassive black holes appearing overnight, that there has to be this accumulation, you get the small black holes merge with other small black holes, they form larger black holes and those make bigger black holes. And then you eventually get ones that are in the hundreds of times the mass of the sun, then thousands of times, then tens of thousands, and then hundreds of thousands, and then eventually you move into those millions of times the mass of the sun.
So it's like this geometric progression of black holes eating other black holes to walk up that chain until finally you get those supermassive black holes. And the supermassive black holes, they're at the hearts of galaxies, which is sort of like the bottom of the gravity well of the galaxy. And so it's not surprising that they will collect down into the middles of these galaxies and then start to merge up.
But we don't see, or haven't traditionally seen, these in-between sizes.
Dr. Pamela Gay: 100,000 to 100,000 solar masses decided it wanted to be invisible.
Fraser Cain: Yeah, nowhere to be seen for the entire, essentially the entire history of astronomy. There has been this surprising gap where you would expect to see, like if you, I guess if you sort of think of a standard distribution curve, there should be lots of the middle sizes and then very few of the biggest ones, the heaviest ones. And yet, in fact, it's like there's lots of the light ones, lots of the big ones and nothing in between.
And that has always been a really big puzzle in astronomy.
Dr. Pamela Gay: And this is where we have to be fair to history and say that prior to the early 2000s, prior to the late 1990s, people were labeling the centers of galaxies monsters. We didn't have this unified idea of active galactic nuclei and CIFRT-1, CIFRT-2s and quasars all being actively feeding black holes. They literally were just saying monsters be here.
And stellar mass black holes, we didn't have the X-ray and gamma ray data we have today. So we had like Cygnus X-1, I think is the correct license plate for this one stellar mass object that we said, that's probably a black hole. But in the late 1990s, we suddenly started to be able to use the Hubble Space Telescope's spectral capabilities to look in the cores of galaxies, look at the radial velocities of things really close into the core and stay there.
That is so high in velocity that the only way you can explain that is with a supermassive black hole. And we also had Andrea Goetz and her team looking at motions in the core of our galaxy and saying these stars can only be moving like this if there is something that is a supermassive black hole. So supermassive black holes really only started to find in the 1990s.
It would take Fermi and Chandra and a whole lot of work confirming things in the radio to figure out stellar mass black holes are actually a thing and they're kind of everywhere. So we're really only looking at 20 years, not even.
Fraser Cain: So I would say one of the big revolutions came with the LIGO observatory.
Dr. Pamela Gay: So with LIGO, we are able to see the release of energy when high mass objects on the small side of what we call high mass decide to merge. So it sounds stupid, but here we're talking about neutron stars. So neutron stars and black holes are the largest stellar remnants.
And the sensitivity of LIGO is really just tuned by nature to be seeing the neutron star mergers and stellar mass black hole mergers. And here I have to check my dates. In 2019, rather, May 21st, 2019, there was a merger that caused a wave of space time that compressed the separation between the mirrors and the LIGO system as it passed through our planet.
There was a gravitational wave released that could best be understood as the merger of an 85 solar mass stellar mass black hole and a 65 solar mass stellar mass black hole into a 142 solar mass intermediate black hole. Now this is a kind of squirrely result because that 85 solar mass black hole doesn't fit what we expected to exist and we can't fully explain it except as the merger of two smaller black holes and the universe hasn't been around long enough to justify that. So we're confused.
Fraser Cain: Right. Right. And that's sort of back to that thing you were saying that there is no direct mechanism for getting you black holes of that 85 times the solar mass that that you can have lighter ones and you can get maybe heavier ones, but it's that there's that gap where they shouldn't be forming because these stars are expecting to just completely blow up and yet there there is one.
And so then you have to say, OK, well, there had to be two smaller black holes that came together to produce that black hole, which is weird because it takes time. You need to kind of take time. Yeah.
Yeah. Yeah. But there it is.
There it is. You know, the universe does. The universe doesn't ask for our permission to show us stuff that that are unexpected.
So OK, so then you've got this this new tool, LIGO, for being able to detect the collisions, the mergers of black holes. And now it's finding this point almost a black hole merger almost every day. It's such a productive observatory.
And so now we're seeing all of these black holes that are out there or at least the ones that are emerging. We're not seeing all the ones that are out there, the ones that are quiet, that are silently moving through the cosmos, interacting with nobody apart from its gravity. But you know, don't worry about those.
I'm sure it'll be fine. But what about the intermediate mass black holes? We've got one at one hundred and twenty five, but that's that's not one hundred thousand.
That's not two hundred thousand. Where are the intermediate mass black holes? Can anybody find them?
Dr. Pamela Gay: Well, so so technically anything over a hundred is an intermediate mass black hole. Now, globular clusters may offer a solution. And this gets highly controversial because.
Several attempts to say this globular cluster or that globular cluster must have an intermediate mass black hole have been confounded by realizing, no, they actually are filled with stellar mass black holes in their core whose additive mass allows things to get flung around as though there were an intermediate mass black hole. The result that is so far standing up the best is Omega Sun, which is a super weird globular cluster. It appears to have had multiple epochs of star formation.
It's the biggest, the biggest, it's chunky, it's best seen from equatorial regions. So if you live in the extreme north, you're probably not going to see it. It's a gorgeous globular cluster that likes to defy expectations.
And because it's a weirdo, people keep looking at it with the Hubble Space Telescope. And a team of researchers realized there is data over enough of the history of the Hubble Space Telescope, which is now 35, which really made me feel old to learn.
Fraser Cain: Don't feel old.
Dr. Pamela Gay: So with many, many, many observations, researchers were able to identify seven stars in the core of Omega Sun that are moving so fast that they should, unless there's an intermediate mass black hole in there, they should be moving at escape velocities and leaving instead of orbiting in the core. Their orbits are consistent with an 8,200 solar mass black hole being in the heart of Omega Sun. So far, no one has been able to disprove these results.
This is the one I'm going to go with.
Fraser Cain: Right. But that is, you know, now we're talking, that is an intermediate mass black hole. That is something that you couldn't get without mergers upon mergers upon mergers.
And of course, in a globular cluster, these are places that are incredibly dense, lots of stars, lots of time for things to find each other. And this is where you would you would find them. So and as you said, this is the strongest case, but there have been other examples where it feels like you can, where astronomers say they see almost like the gravitational wake of these intermediate mass black holes moving through globular clusters, distorting the movements of the other stars around them.
But obviously, it's a very tricky observation to make. And so they haven't held up as strongly. So up until this point, I think, you know, we've I've been covering this on Universe Today.
We've had lots of these like tentative discoveries. Is this some indirect evidence? I don't know.
There's, you know, but now the evidence is starting to build.
Dr. Pamela Gay: And this is where we get the dark energy spectroscopic instrument DESI. And it is my new favorite thing. Gaia had been my favorite thing.
DESI is now my favorite thing.
Fraser Cain: In this brief break between Gaia and Vera Rubin, we get a new favorite thing.
Dr. Pamela Gay: Yeah. And DESI is a instrument that is going through and taking spectra of galaxies in numbers that are ludicrous. They looked at their initial data.
This is not the full survey. This is preliminary release. They started with spectra of 410,000 galaxies.
They found 115,000 of these were dwarf galaxies. And because they have such high resolution and tiny fiber optics, they're able to resolve smaller things than could be resolved in the past, which means we can start to see and understand smaller things than we could understand in the past. Things that in the past just got blurred out by the stars and things around the cores of galaxies.
Fraser Cain: Yeah.
Dr. Pamela Gay: And they were able to find that of these 115,000 dwarf galaxies, 2,500 have active galactic nuclei, which is not something we've really expected. And they also found 300 intermediate mass black holes.
Fraser Cain: Mini quasars at the centers of dwarf galaxies that are active. They are feeding and they are blasting out radiation in exactly the same thing that we see with quasars, just at a much smaller level. And so what kinds of masses do we think we're looking at in these dwarf galaxies?
Dr. Pamela Gay: This is the thousands to tens of thousands that- Done. Yeah. We got there.
Fraser Cain: Yes.
Dr. Pamela Gay: And what I love is we're now having to figure out between the data from the James Webb Space Telescope that's like, hey, galaxies formed way before anyone thought. We are now having, because of DESI results saying here are these intermediate mass black holes everywhere that are actively eating, because of the LIGO results saying, hey, we have mass gap black holes. We're having to start thinking about things that weren't even the topics of graduate school conversation at the beginning of this century.
Things like intermediate mass black holes that maybe came out of primordial prior to the cosmic microwave background release times. We're having to talk about, well, are these things forming as the galaxies form through turbulence at all sizes?
Fraser Cain: Direct collapse. Yeah. Are we seeing first generation stars being able to be much larger and more massive than anyone thought, producing larger remnants, going straight to intermediate mass black holes?
Like these mysteries are compounding.
Dr. Pamela Gay: And so we're at this really cool point where theorists are going nuts. We're trying to figure out, okay, realistically, what fits the data the best? And we're going to see the extremely broad brushstrokes that we used to explain the bulk of evolution of stars and galaxies in our universe getting radically evolved as we add in new details about things that happened early on, those first stars, what happened prior to the formation of the cosmic microwave background.
All of these things caused effects we are finally able to see for the first time. So it's not that we were wrong in the past. In some cases we were wrong.
It's that we're now realizing our ideas about the universe were way too limited because as you said, the universe doesn't ask permission and it was more creative than we were. And it's really cool.
Fraser Cain: Yeah. Yeah. And like it really feels like we're seeing other examples like the little red dots that were discovered by James Webb, that the large structures of the universe formed really early on that mass came together quickly and that, as you said, something had to overcome that turbulence in order to be able to bring this material closer together.
Because we just, we don't see that happening in stars today, you know, beyond a hundred times the mass of the sun, the outflows of radiation become so strong that no new mass can fall in. Well, how do you get us, how do you get a, even an intermediate mass black hole with tens of thousands of times the mass of the sun within, well, how do you get a billion mass black hole within the first 800 million years of the beginning of the universe, right? Like that's crazy.
Well, so there has to be some kind of direct mechanism that's coming together, that's forcing matter and energy into these small regions and allowing them to turn into black holes on scales that were vastly quicker than anybody had ever thought. And this is the regime that we're now apparently living in. So there's one piece of research, I don't know if you had prepared this, but astronomers have found stars getting ejected on hypervelocity trajectories out of the small Magellanic cloud, which is our closest example of a dwarf galaxy.
And that you can't get this without there being an intermediate mass black hole that's going through three body interactions, hurling stars at us.
Dr. Pamela Gay: Yeah. And that's one of those results where people are like, let me see if I can come up with something else. So it's one of those results that isn't a, it absolutely has to be this.
It is one of those results where it's like the easiest way to explain this is with an intermediate mass black hole. So yeah, it turns out the Magellanic clouds fling stars. And one star has been seen moving with a sufficiently high velocity that the easiest way to explain it is you have two stars left behind in the tight binary and it got flung out in the process.
So you probably had an intermediate mass, a black hole and a binary system and it got shredded.
Fraser Cain: Right. Tore one of them away and the other one got a slingshot out of the galaxy. And so it's interesting, you know, the fact that so many of these intermediate quasars, I don't know how you describe them.
We need a new term for the mini quasars anyway, mini quasars. These mini quasars have been found at the hearts of many dwarf galaxies. Then you can start to make this assumption that in the way we know that there is a supermassive black hole at the heart of every large galaxy, there could very well be an intermediate mass black hole at the heart of every dwarf galaxy.
Dr. Pamela Gay: And this is where dwarf galaxies are super weird. And we are learning you can't actually say every dwarf galaxy regarding anything. There was a point in time where we were like, dwarf galaxies have extremely high light to dark matter ratios.
And then we found some that appear to have no dark matter.
Fraser Cain: Yes. Yeah. Or stars.
Dr. Pamela Gay: Yeah. Dwarf galaxies are weirdo leftover chunks of stuff and things that, yes, some of them appear to have intermediate mass black holes that are actively feeding. Others appear to have had a single epoch of star formation and be in terms of their stellar population identical to a globular cluster, but with radically different motions and strange dark matter ratios.
They are weird. They're the small leftover bits that apparently do what they feel like.
Fraser Cain: So this is satisfying, I think, for me, that we are finding at sort of three different methodologies that we have available to us now through gravitational waves, through examining the motions of stars in globular clusters, and through looking at the radiation that's coming from the centers of dwarf galaxies, growing evidence that there are a lot of intermediate mass black holes. And one of the biggest mysteries in astronomy feels like it's now starting to give up its secrets. We're starting to learn the true answer to this question, which is just, it's so great.
Dr. Pamela Gay: And it's a really interesting time because every time we get an increase in computational ability and an increase in telescopic ability, we see these revolutions. The last one was with the Digital Sky Survey. Gaia did a lot for motions and figuring out where things are in stellar populations.
But when it comes to galaxies, DESI is that next revolution, and I'm here for it.
Fraser Cain: Me too. Thanks, Pamela.
Dr. Pamela Gay: Thank you, Fraser. And thank you so much to our patrons. We would not be here without you, because it turns out we need a small herd of people to make us sound good.
This week, I would like to thank AstroBob, AstroSets, Bebop Apocalypse, Bob Zatzke, Brett Moorman, Danny McGlitchie, David Troge, Diane Philippon, Dr. Whoa, Flower Guy, Frederick Salvo, Galactic President Scooper, Star McScoops-a-Lot, Jeff McDonald, Glenn McDavid, Gold, Gordon Dewis, James Signorowicz, Jarvis Earl, Jim Schooler, Jordan Turner, J.P. Sullivanm, just me and the cat, Justin Proctor, Christian Golding, Kinsaya Penflanko, Matthew Horstman, Maxim Leavitt, Michael Wichman, Nate Detweiler, OldBoomer847, Paul D. Disney, Peter, Rajevs, Akari, Robert Cordova, Robert Hundle, Robert Plasma, Sergio Sansevero, Sersom Scone, Scott Bieber, Scott Briggs, Sean Matz, Semyon Torfason, Siggy Kemmler, Stephen Veidt, Stephen Coffey, The Mysterious Mark, Tricor, Van Ruckman, and Zero Chill. Thank you all so very much.
Fraser Cain: Thanks, everyone. We'll see you next week. Bye bye.
Live Show
When enormous stars detonate as supernovae they release a burst of neutrinos that can be the first sign of a coming explosion. Now, astronomers have built a network to watch for that flash of neutrinos, and help direct their telescopes for when the sky show begins. Supernovae explosions occur in stages, with neutrinos being emitted hours before photons. If we can accurately detect those neutrinos, we might just be able to get on target before the light show even starts.... Maybe.
Show Notes* Celebrating the 750th episode of Astronomy Cast. * Topic Overview: Exploring how neutrino detection can provide advance warnings for supernova events. * Understanding Supernovae and Neutrinos * Supernova Mechanism * Role of Neutrinos * Detection Timing * The Supernova Early Warning System (SNEWS) * Significance of Early Detection * Scientific Benefits * Challenges * Historical Context * Supernova 1987A * Impact on Astronomy * Future Prospects * Advancements in Detection Technology * Integration with Electromagnetic Observations * Importance of SNEWS
TranscriptFraser Cain: AstronomyCast, Episode 750, The Supernova Early Warning System. Welcome to AstronomyCast, our weekly facts-based journey through the Cosmos, where we help you understand not only what we know, but how we know what we know. I'm Fraser Cain, I'm the publisher of Universe Today.
With me as always is Dr. Pamela Gay, a Senior Scientist for the Planetary Science Institute and the Director of CosmoQuest. Hey Pamela, how are you doing?
Dr. Pamela Gay: I am doing well. Happy 750th episode, Fraser.
Fraser Cain: This is it, 750 episodes, and we're going to celebrate by producing an episode of AstronomyCast.
Dr. Pamela Gay: Which is like science, science. We need science.
Fraser Cain: That's just what we do. That's why we're here. So when enormous stars detonate a supernovae, they release a burst of neutrinos that can be the first sign of a coming explosion.
Now astronomers have built a network to watch for that flash of neutrinos, and help direct their telescopes for when the sky show begins. So before we get into all of the really cool science and the network itself, and I think people are going to go, wait, wait, wait, what? You see the neutrinos before you see the light from the supernova?
That's weird. I thought neutrinos can't, nothing moves faster than the speed of light, the supernova is moving at the speed of light. How do we see the neutrinos first?
Dr. Pamela Gay: So neutrinos do move slower than the speed of light. They do have mass. They are moving exceedingly fast, like it took us forever, it felt like, to figure out if they had mass or if they didn't because their speed was close enough to the speed of light that it was within error.
We're talking about neutrinos from galactic or near galactic supernovae, so like the Large and Small Magellanic Cloud, close enough.
Fraser Cain: Or in the galaxy, right?
Dr. Pamela Gay: Yeah, so galactic supernovae or near galactic. And because there's a several hours lag between the neutrinos coming out and the first detection of light, that allows something moving near the speed of light to reach us before the light does.
Fraser Cain: Right, but why? Oh, sorry. How do we see the neutrinos before we see the light?
Like if we saw Betelgeuse go off and it's only, say, 640 light years away, we would get the neutrinos before we saw the light from the supernova. Why?
Dr. Pamela Gay: It all has to do with the fact that the neutrinos are just going to fly through everything for the most part. Some will interact. Whereas it takes time for the outer parts of the star to first of all figure out they're supposed to be glowing differently.
And second of all, for that light from inner parts of the star to escape through all that medium where it's going to get absorbed and re-emitted and absorbed and re-emitted and get a lot of Brownian motion going on.
Fraser Cain: Right, right, right. I mean, we talk about this idea of this random walk that photons have to make to even get out of the sun in the first place. That when you have fusion at the core of the sun and it produces a photon of gamma radiation, that then gets absorbed by another atom.
And then that has to re-emit it, and then that gets absorbed, re-emitted, absorbed. And it can take 100,000 years from when a photon is generated at the center of the sun to when it actually reaches the surface. Now is it the same photon?
It's been absorbed, re-emitted, and so on, but that's the gist of the dilemma. But a neutrino, we've talked about this, they'll go through a light year of solid lead, no problem. The interior of a star is nothing.
It is like glass, light shining through glass to them.
Dr. Pamela Gay: And the time scales for all of this happening is kind of wild. You end up with supernovae happening in a couple of different scenarios where the core of the star suddenly becomes degenerate. The one that we talk about most is iron.
The center of the star builds up into heavier and heavier atoms. It gets to the point where it has Fe, iron, in the core, and it goes to try and fuse two of these atoms together, and the atoms go high. We need to have energy added to us if you would like to do that.
Everything that's lighter mass, you go to add them together, and they release energy. It's at Fe, it's at iron, where we have this sudden switch to the binding energy of the larger atom is going to need to have energy added into it.
Fraser Cain: It's so shocking to me how instantaneously this happens, that up until iron, you've got this outward light pressure that's coming from the interior of the star that's pushing back against all of the mass that is trying to pull itself together. You have this balance, this hydrostatic equilibrium. As it moves up that chain of elements, you reach that point where you get to iron, and it's like a light switch.
It just shuts off the entire star in a fraction of a second, and now suddenly there is no outward pressure, and the whole star just collapses inward. It can get up to 70% the speed of light, and it is falling into the very center of this star. It's ludicrous.
Dr. Pamela Gay: One of the calculations I ran across while prepping for this show was the 5,000 kilometer across core that is iron will collapse down to about 20 kilometer across neutron degeneracy pressure supported neutron star in like one second.
Fraser Cain: One second. Yeah. Just boom.
All of that material is hammering the core to make that collapse, and you get neutrinos from the highest energy reactions in the cosmos. You get an enormous amount of neutrinos that are formed in this moment, and they instantly escape while, as you said, the light and the matter is trying to figure out what to do. Do I move over here?
Do you go over there? What's going on here? Finally, you get this flash of radiation on the surface of this star that then continues to glow and grow, and it gets brighter and brighter and brighter, but the neutrinos are already gone.
Dr. Pamela Gay: Yeah.
Fraser Cain: They're already out.
Dr. Pamela Gay: The neutrinos are like every flavor, every style. The number of ways that neutrinos are getting created is kind of crazy. First of all, you have as the core collapses, you have the protons and the neutrons going eek, eek.
The protons with the electrons are combining. They are producing neutrons and anti-neutrinos. Then you also have some of the protons and electrons are liberating themselves because neutrons are not stable.
You have beta decay and inverse beta decay producing electron neutrinos and anti-matter electron neutrinos via both these mechanisms. Now, creating the neutron core is the easy one to think about, but you also do have the neutrons that are going back into protons and electrons periodically. Then, you also have all the thermal radiation that's coming out where you have a ton of positrons and a ton of electrons that are going to annihilate against each other, producing light, producing neutrinos.
So, you have particle annihilation, which is a thermal production. We still don't have any evidence of it, but there's also theoretical concepts that photons interacting with particles could also produce neutrinos. Yeah, it's wild, all the different things that are spontaneously going on, all because the center of the star gave up the ghost of potential energy.
It's something like 99% of the gravitational potential energy of the star gets converted into neutrinos.
Fraser Cain: All right, so we understand the underlying science that we get this cool trick that we can observe forthcoming supernovae. What is the Supernova Early Warning Network?
Dr. Pamela Gay: It is a network of a variety of different neutrino detectors that work in a variety of different mechanisms, from water to scintillation fluid to you can actually have these things that use lead. All these different methods of detecting neutrinos at all these different sites around the world are all unified in a collaborative agreement to share data, and if they suddenly get a flux of neutrinos, and we've seen this before with Supernova 1987A. We have seen neutrinos from other things like neutron star, neutron star mergers.
They're there, and if they all detect these, they should have slight timing variations. These slight timing variations are because of the path difference to each of these different places in three-dimensional space on the planet Earth. If you have enough different places with enough accurate clocks, you can figure out where on the sky to point your telescopes.
Because the neutrinos are coming out significantly hours before the photons should be detectable, there is a chance that we will be able to see a star from moment zero of light being given off.
Fraser Cain: This is a big unsolved mystery in astronomy, that we catch supernovae after they've happened. Now, there are the occasional fortunate survey where someone surveyed a chunk of the space, and then one of those stars detonated as a supernova months or years later, and then they come back around, and they're able to compare, and like, oh, it was this star, and then it detonated as a supernova. But nobody has seen those first moments, the initial brightening, the initial flash of radiation that happens in whichever order it does.
That has never been seen before, and so the hope is on the supernova warning network. Now, we know that we got that flash of neutrinos coming from supernova 1987A, but we didn't have the warning network, right? Right.
Like, maybe something they puzzled out long after the actual supernova had been visible in the telescopes. It was like, hmm, we see an increased amount of flux here, oh, that was coming from the supernova.
Dr. Pamela Gay: And let's face it, back in 1987, neutrino detections were still new. This was still new science. We only had a few detectors in the world.
Now we have more like a dozen-ish detectors in the world, and by having more understanding, we now know that they switch identities. Neutrinos aren't big on staying who they're born as, so they'll switch flavors between electron, muon, all these different varieties. They do stay either matter or antimatter.
That is locked in stone. You also have just all these different ways that we detect them again, so this is allowing us to start to see them at a variety of different energies. We weren't there yet in 1987.
Now we're there.
Fraser Cain: Mm-hmm. Mm-hmm. And so, how many neutrino events, how many supernova has the Warning Network detected?
Dr. Pamela Gay: Zero.
Fraser Cain: None.
Dr. Pamela Gay: It has found none. Our galaxy is being super annoying, so it is anticipated that a galaxy like ours will have a supernova about every century. So it's not quite one per century.
That's what you'll find commonly written. It's actually more like 0.8 a century, or every couple of centuries, and three a century. We should be detecting these things.
Fraser Cain: But when was the last bright supernova that we saw in the galaxy?
Dr. Pamela Gay: Kepler supernova, 1604, was the most recent. 1604 is more than 400 years ago. So they're behind schedule.
Yeah, and so here's the thing. If a supernova goes off in a super dusty region, we may not see it. The neutrinos will be released, so we're now in a position to see things we couldn't see before.
Fraser Cain: I mean, like the other side of the Milky Way.
Dr. Pamela Gay: Yeah, exactly. A lot of these star forming regions, super dense with dust, supernovas occur in star forming regions. So there is a chance there have been supernovae that we simply haven't been able to see because they were obscure by all of the dust in the disk of our galaxy.
Fraser Cain: Okay, so let's imagine that we do get a flash of a supernova. Something goes off in our vicinity. Maybe not Betelgeuse close, but 10,000 light years close.
Play this out for me. What will happen?
Dr. Pamela Gay: So what we expect to happen is there will be a wave of neutrinos that hit our planet passing through the planet. The detector that is closest to this incoming wave on our spherical world will detect the neutrinos first. As that wave passes through the planet hitting each of the neutrino detectors on our world as it goes through, detectors will have signals.
This will allow us to figure out the timing if everything works and all the atomic clocks are properly synced and everything else. This will allow us to figure out where on the sky to point. Now, hopefully in an ideal universe, that side is in darkness and all of the detectors on that part of the planet point that direction.
Fraser Cain: I didn't even think about that. You've got like a 50-50 shot about whether or not it's going to be daytime or nighttime, and so then you're going to have to depend on the space telescopes to be able to see And what's even worse is if it's within 30 degrees of the sun, we can't even point the space telescopes there because it will blast them. And that's crazy.
You could get a flash of neutrinos that are from a supernova that goes off on the other side of the sun. It would go right through the sun, no problem, right through the earth, no problem. And we would detect it, but we can't look at it.
I don't know, maybe like a mission like New Horizons or something that's in a different perspective could take a shot of the supernova, but that would not compare to the combined light-gathering capacity of the earth's and space telescopes that we have arrayed around our planet. That would suck.
Dr. Pamela Gay: Yeah. Yeah. So, so there is that, that issue now, assuming that it occurs in a part of the sky where we can observe it, we get all of the, the most important at this point are the highly sensitive wide angle cameras, because we're not going to, with a timing method, have it down to the tiny, tiny sliver of the sky that something like Hubble is able to look at.
So we're going to need to look with the wider angle cameras. Luckily we're starting to get more and more space-based wider angle cameras.
Fraser Cain: Like Euclid or upcoming Nancy Grace Roman or things like that.
Dr. Pamela Gay: Sphere, things like that. Yeah. So, so you look with the wider angle cameras, software says, Hey, this bright thing didn't used to be here.
Study, study, study. The key things that we're going to be looking for are the evolution of emission lines. The thing that generates the light in supernovae that creates that wild light curve that we're so used to seeing is the radioactive decay of a variety of different elements.
So as you get these different transitions, this, this is where nickel is one of the great blames for supernovae light curves. For instance, this allows us to see the emission lines and it allows us to see the, the shock wave illuminated over a period of days and weeks. Now there, there are two scenarios that are possible that, that will be very interesting.
One of them scientifically interesting. The other, Oh shoot, this will allow us to explain the lack of observations for 300 years. So assume that something like this goes off night side of the planet.
Everything's looking, everything's looking, nothing is seen. This will allow us to say this most closely aligns with these star forming regions, all of which have massive amounts of dust in place, a limiting magnitude of if it was in these magnitude ranges, we wouldn't have seen it. So that starts to tell us, didn't see it.
Now the other thing that could happen is it's theorized that you can have core collapse without having a visible supernovae. Now if you have core collapse without a visible supernovae, that, that means you can look and look and there's no light, but you do get the neutrinos.
Fraser Cain: Right. So like a, like an unknown, like a star just disappearing, collapsing in on itself and it not being able to create the supernova. And that's interesting.
I mean, we've seen examples of stars just disappearing from the sky and it's been thought that maybe that's what's going on, that it was there and then it imploded and it was very efficient and ate its, ate the entire plate, right? And just collapsed it all into a black hole, which is mind blowing. And then that would explain why we haven't seen the supernova maybe.
And but as you say, there would be this flash of neutrinos even though, and so that would be even more sign that we detect the flash of neutrinos. We look in the direction where it supposedly came from and there's nothing there.
Dr. Pamela Gay: Yeah. Yeah. So that's the super interesting.
Fraser Cain: Yeah. And then the surveys show that there's a star missing.
Dr. Pamela Gay: Right. That would be great. That would be ideal.
Now, the probability of something like that happening is fairly low. This is not one of the common forms of things happening that we expect. But these are all the possibilities that the supernova early warning system is looking for and they, they have a really cool network.
It is funded by multiple funding agencies across the planet. This is international. It engages amateurs through the American Association of Variable Star Observers, which is not just Americans.
It was just named over a hundred years ago. And so there's people out there ready for these neutrinos to be detected, ready to point in the correct swath of the sky. This is kind of like the gamma ray burst alert network that we had in, in the early two thousands when we were still trying to catch optical afterglows of gamma ray bursts for the first time.
I mean, we've seen them for the first time, but for like common times now, gamma ray afterglow is just like another day at the office and it's the neutrino afterglows that we are chasing with fervor.
Fraser Cain: Yeah. Yeah. Yeah.
And so hopefully the next time that bright supernova, that nearby supernova goes off in the Milky Way, we will be ready. And, and the, you know, the supernova early warning network is the first step. There are other plans in the works I've reported on this, that they're looking to build more powerful versions of this, more sensitive versions that you could expand outward.
And the goal would be to encapsulate Andromeda and Triangulum and try to bring more galaxies into this network. And that, you know, theoretically galaxies that we see within tens of millions of light years are giving off supernova and eventually we'll get to this place where we'll see them every couple of years and we will have the ability to, to watch them as they unfold. But nothing would be as, as powerful as seeing one that goes off, you know, Betelgeuse distance.
Dr. Pamela Gay: Yeah. And it's all about increasing the sensitivity of these systems. When a supernova goes off, all those neutrinos fill a, they go off in all directions, assuming symmetrical supernova, you have to do that sometimes.
And so the further away something is, the smaller the cone of that sphere of neutrinos we're going to be able to detect. By increasing the sensitivity of our neutrino detectors, we start to be able to see supernovae going off further away. We start to be able to tap into the cosmological background neutrino flux.
There's so much cool science to come out of this and, and I'm here for it and we will be here for it for...
Fraser Cain: Totally.
Dr. Pamela Gay: Yeah.
Fraser Cain: Hopefully, I can't wait to report on the first detection with the, with the network. All right. Thanks Pamela.
Dr. Pamela Gay: Thank you, Fraser. And thank you to all of our patrons out there who've been there with us over and over through the years. All right.
This week, I would like to thank David Resetter, Travis C Porco, Mike Husey, Jonathan Poe, R.B. Basque, Jimmy Drake, Bob Crail, Tricor, Noah Albertson, Ryan Amari, Mike Dogg, Simeon Torfason, Mark Schneider, Michael Purcell, Jeanette Wink, Brian Cagle, Jason Kwong, Tiffany Rogers, Robert Plasmo, Laura Kettleson, Red Bar is watching. A pronounceable name. You're welcome, doctor.
Jeremy Kerwin, Kinsaya Pamflenko, Cherisom, The Lonely Sandperson, Scott Briggs, Benjamin Carrier, Jim Scholar, Marco Arasi-Nayla, David Green, Smansky, Rando, Benjamin Mueller, Benjamin Davies, Planetard, John Drake, Bruce Amazine, Paul L. Hayden, Jeff Hornmurder, Pauline Middleink, Jordan Turner, Robert Hundell, Taz Tooley, Lee Harbourn. Thank you all so very much.
Fraser Cain: Thanks, everyone. And we'll see you next week.
Dr. Pamela Gay: Bye bye.
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After the cosmic microwave background radiation was released, the Universe returned to darkness, cloaked in this clouds of primordial hydrogen and helium. Gravity pulled these vast clouds into the first stars, and then the first galaxies. This is Cosmic Dawn, and JWST will help us probe this mysterious time.
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In 2017, astronomers detected the gravitational waves and electromagnetic radiation from colliding neutron stars. This had been long theorized as one of the causes of a certain type of gamma-ray burst. By studying the event and its afterglow, astronomers have learned a tremendous amount about the formation of the heaviest elements in the Universe.
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Most stars in the Milky Way are trapped in here with us, doomed to orbit around and around and around. But a few have found a way out, an escape into the freedom of intergalactic space. How do stars reach escape velocity, never to return?
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The Sun is a third-generation star, polluted with the metals from long-dead stars. Astronomers have also discovered second-generation stars, with very low metallicity. But theories suggest there must be a first generation, with stars made from only pure hydrogen and helium. Can we ever find them?
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Show NotesThis episode is sponsored by BetterHelp. Give online therapy a try at betterhelp.com/ASTRONOMY and get on your way to being your best self.
NASA Artemis (NASA)
JWST (NASA)
DART (JHUAPL)
Chinese space station epitome of aerospace workers’ wisdom: designer (CGTN)
InSight Mission – NASA’s InSight Mars Lander (NASA)
Overview | Sun (NASA)
Stars – Stellar Populations (Astronomy Online)
What is stellar magnitude? (EarthSky)
Population I (Swinburne University)
Population II (Swinburne University)
Population III (Swinburne University)
What is a globular cluster? (EarthSky)
Two planets around Kapteyn’s star: a cold and a temperate super-Earth orbiting the nearest halo red dwarf (MNRAS Letters)
Pair-Instability Supernovae: What might they look like? (Astrobites)
Gamma radiation (ARPANSA)
Hydrostatic Equilibrium (Swinburne University)
Positron (Swinburne University)
Potential First Traces of the Universe’s Earliest Stars (NOIRLab)
Quasar (Swinburne University)
Gravitational Lensing (Hubblesite)
PDF: First Stars and First Light: The Epoch of Reionization (NSF)
What is the Cosmic Microwave Background? (Universe Today)
New insight of AGC 198691 (Leoncino) galaxy with MEGARA at the GTC (MNRAS)
Elemental Abundances (Center for Astrophysics)
Hubble Space Telescope
American Astronomical Society
241st AAS Meeting (AAS)
Supermassive Black Hole (Swinburne University)
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TranscriptTranscriptions provided by GMR Transcription Services
Fraser Cain: Astronomy Cast, Episode 664: The First Stars.
Fraser Cain: Welcome to Astronomy Cast, your weekly facts-based journey through the Cosmos, where we help you understand not only what we know, but how we know what we know. My name is Fraser Cain, I’m the publisher of Universe Today. With me is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the Director of CosmoQuest. Hey, Pamela, how are you doing?
Dr. Pamela Gay: I am doing well. How are you doing?
Fraser Cain: Good, good. So, we did a wrap-up of the space news in 2022 and – while 2022 like many years sucked – for space it was the best, right? We had Artemis, we had the James Webb space telescope, we had DART, we had the Chinese space station, we had so many amazing things come together. It feels like it was probably one of the best years in space in my career. So, it’s amazing. It was an amazing year and I don’t see as many exciting things coming up for 2023, but who knows?
Dr. Pamela Gay: That is true. See I’m still mourning InSight. The InSight mission was my favorite little Mars sitter/lander.
Fraser Cain: But it lasted twice its lifetime.
Dr. Pamela Gay: It did. And so I guess I’m still mourning. I’m still mourning the little lander that tried so hard.
Fraser Cain: Well, what more could you have asked for it, right?
Dr. Pamela Gay: A giant earthquake.
Fraser Cain: It should have lasted for four times as long? Ten times as long? They can’t all be opportunity.
Dr. Pamela Gay: I know. I know.
Fraser Cain: Right. All right. The sun is a third-generation star polluted with the metals from long-dead suns. Astronomers have also discovered second-generation stars with very low metallicity. But theories suggest there must be a first generation with stars made from only pure hydrogen and helium. Can we ever find them? So, first, please explain the generation numbering scheme for stars because it’s ridiculous.
Dr. Pamela Gay: Okay.
Fraser Cain: We have a pop I star?
Dr. Pamela Gay: Yeah. Astronomers –
Fraser Cain: And there are pop II stars?
Dr. Pamela Gay: Astronomers shouldn’t be allowed to name things or set the directions of calibrations. So, just like astronomers screwed up in terms of calling the brightest stars magnitude zero – meaning faint stars are magnitude 20 – we decided that our current population is number I. We’re number I.
Fraser Cain: Right because we’re the first star that we ever discovered.
Dr. Pamela Gay: Well, yeah, we are the first star we ever discovered sort of I guess. You fell asleep the first night and then you found all the rest of them?
Fraser Cain: Yeah.
Dr. Pamela Gay: But anyways, so the generation of stars older than us – that doesn’t have as many metals – can’t probably form planets the same way. Those are population II and as illogical as it can possibly be, the first generation of stars the universe ever formed is population III.
Fraser Cain: Right. So, it makes sense. The first star that we ever discovered, they’re population I. The second stars that we ever discovered; those are population II. And then we’re hoping someday we’ll find the third stars – the type of stars – which will be population III, still theorized. Okay. So, that is the – and then how do you define them? As an astronomer, when do you take a star and put it into the pop I bucket and put it into the pop II bucket, and the theoretical pop III bucket?
Dr. Pamela Gay: So, pop III means these stars are primordial ingredients. They are made of the exact same stuff that was produced in the Big Bang – hydrogen, helium, maybe a trace amount of lithium and beryllium – definitely a trace amount of lithium and beryllium. But then pop I are all the stars like our sun that are being formed currently. These are things that are two to three percent of atoms heavier than hydrogen and helium and the stuff in between is the population II.
So, once you start getting to the point – and I’m sure this is gonna get redefined as the formation of planets plays a larger and larger role – but pretty much once you start getting to the point that you’re not seeing planets forming, that’s where you have population II stars.
Fraser Cain: Although I’m sure someone’s found planets are on pop II stars or will shortly?
Dr. Pamela Gay: The issue is population II stars these are objects that are generally less than a percent of heavier atoms. And if you don’t have heavier atoms, you can’t form planets. So, one of the amazing things is globular clusters out there. These are population II stars orbiting our galaxy. They don’t have planets so far and we have looked as hard as we can possibly look at things that far away and they’re just not showing up.
Fraser Cain: So, there’s one known type II star that has a planet?
Dr. Pamela Gay: Are we sure, sure?
Fraser Cain: Well, it’s called Kapteyn’s Star. It’s a M1 red sub dwarf and the metallicity is about 14% of the sun, which classifies it in the type II star.
Dr. Pamela Gay: How do you always find these exceptions?
Fraser Cain: Because I have a hunch. Look, okay, look. Here’s my standard operating procedure, right, is that I think all I do is report on surprising new discoveries and new things moving forward and so it just it feels like somewhere there is a headline, “Astronomers find the first planet around a type II star.” Yeah, anyway, and I’m sure they’ll find many more because “Astronomers shocked to discover. Theories overturned.” So, yeah, all right, we’re gonna talk more about the first stars in a second – which we know we don’t know of any. Or do we?
Dr. Pamela Gay: It’s true. We don’t yet.
Fraser Cain: We’ll be back in a second. Oh, wait a second. I may have news for you then. We’ll be back in a second.
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Fraser Cain: And we’re back. All right. So, we’ve classified the pop I star, the pop II star. Let’s talk about the pop III. So, these are theoretical. As you say, they are made of the pristine material left over from the Big Bang – pure hydrogen and helium – at the exact constituents left over when the universe had cooled down that these atoms could form. How would they be different from a star like we have today? I’m gonna guess no planets, but then even that like I’m sure at some point somebody’s gonna be like, “We found planets around – We discovered pop III stars and we also discovered a planet” a gas giant, who knows?
Dr. Pamela Gay: All right.
Fraser Cain: Pop III gas giants. Yeah, please continue, but what would they be like?
Dr. Pamela Gay: All right. So, one of the weirdest things in trying to understand stars is what are the effects that these heavier elements have on the ability of the star to form and radiate heat? And it turns out that if a star is made of pretty much just hydrogen and helium, the light that is forming in its core just radiates out. And because it’s radiating away and not interacting as much with the protons and electrons because the energy levels just aren’t right, the star is able to become much more massive before it starts pushing out its outer layers, and a star that’s more massive – in this case 100 to 200, 300 times the mass of our sun – it’s only going to live for a million-ish years.
So, we’re in this situation where the very first stars formed roughly 100 million years after our universe formed and then they only lived for a million years before they underwent this super-weird form of supernova where the star essentially eats itself from the inside out, and leaves nothing behind except for a spray of light and heavier elements.
Fraser Cain: So, you don’t get a black hole. You don’t get a neutron star. You just get the thing detonating completely?
Dr. Pamela Gay: It’s called a pair-instability supernovae and –
Fraser Cain: Can you talk about this? You say it eats itself from the inside out, but what is actually happening with pair instability?
Dr. Pamela Gay: So, you have – in the core of the star – gamma-ray photons are getting produced. And these extremely high energy gamma ray photos they’re going to be interacting with protons, with electrons – and not as efficiently as if they were metals – and they’re also going to be interacting with each other. And ideally, the rate of energy production is such that the star is in thermodynamical equilibrium. Gravity is pushing inwards, heat and light are pushing outwards.
Again, the light isn’t as effective here because it’s mostly just flying through the atoms. And when these gamma rays interact with each other, they will produce an electron and a positron. This is a particle and an antiparticle that are able to then later interact with each other if they hit each other later and produce more gamma rays but – because of the kinetic energies involved – some of the energy is lost in this process. The lower energy gamma rays are going to lead to a changing situation where the outer layer of the star isn’t being supported as well. The star begins to collapse down.
As the star collapses down, it heats up. More gamma rays are produced. Gamma rays interact with each other because there’s more of them. It’s easier for them to interact. They produce more positrons and electrons. These interact and annihilate and the star is literally eating itself out of having matter and energy through the loss of energy to kinetic energy. It’s wild and what gets me is we think we may have actually been able to see the chemical fingerprint of one of these kinds of supernovae in the light of distant quasars.
Fraser Cain: Okay. Well, that was the evidence I was gonna bring up.
Dr. Pamela Gay: Yeah.
Fraser Cain: So, then, yeah, yeah. And so I mean we see those pair-instability supernovae. We’ve seen these detonations before but just from heavier stars.
Dr. Pamela Gay: Right.
Fraser Cain: Just stars with other elements like pop II or pop III – pop I, sorry. I got to keep this straight. But the second and third-generation stars but they’re very massive.
Dr. Pamela Gay: Yes.
Fraser Cain: They have exploded as pair-instability supernovae and just completely vaporized themselves – no black hole, no neutron star.
Dr. Pamela Gay: Right.
Fraser Cain: Just kablooey.
Dr. Pamela Gay: Yeah.
Fraser Cain: Yeah. Okay. All right. So, they [inaudible]. Now you were starting to make some estimates of their masses – 100 times the mass of the sun, 200 times the mass of the sun. Do we have a sense of how big these things can get?
Dr. Pamela Gay: This is where you end up with a lot of different people arguing in the literature. There are some folks that are like, “Above 300 solar masses, the energy being produced is going to cause no additional material to be able to fall onto the star. It’s going to be quenched.” There are those that are like, “At 150 solar masses, that’s gonna happen.” There are those who are like, “At 1,000 solar masses, that’s going to happen.”
Fraser Cain: Right.
Dr. Pamela Gay: The safe bet is it’s occurring in the hundreds of solar mass range because – as you pointed out – we do see some massive stars in our modern universe. These are objects that are 150 solar mass to 200 solar mass when they first form and they do have these pair-instability supernovae when they die. So, just how big the very first ones get? We’re looking at hundreds is a safe bet, but exactly how many hundreds we’re not sure.
Fraser Cain: And there could be all kinds of weird dynamics that are going on. There could be magnetic field lines, there could be accretion disks, there could be ways to get beyond pushing that material back away from the star and that’s why it’s – I saw a simulation where they thought that maybe you could get into the tens of thousands of times the mass of the sun.
Dr. Pamela Gay: Yeah.
Fraser Cain: They’re crazy. And then what is a supernova? They simulate in a supercomputer what a supernova would look like when a 50,000 solar mass star goes through this pair instability process.
Dr. Pamela Gay: And then that light doesn’t get very far because the early universe was not yet ionized again, re-ionized.
Fraser Cain: Right.
Dr. Pamela Gay: So, all of this is going on behind opaque layers of gas hiding from us.
Fraser Cain: Huh. We think about these. Sorry. We think about the cause of microwave background as this like someone came and turned off a switch, but it wasn’t like that.
Dr. Pamela Gay: No.
Fraser Cain: It was this long, slow, gradual process of the clouds lifting over the course of several millions of years. And so could you have had these first-generation stars forming within this fog of the early universe?
Dr. Pamela Gay: Yes. That’s exactly where they would have been forming and we’re starting – through gravitationally lensed galaxies – to be able to see the age of reionization, to see early galaxies that still have these clouds of neutral gas around them. But the very first generation, the closest we can come to hoping to be able to find them is that there are pockets of gas out there that just somehow got isolated and left alone for the fullness of time and there’s one – AGC198691 – I have to look at its license plate number.
It is one-twentieth of a percent made of atoms heavier than helium and it has one-fortieth the metallicity of our sun, which means that it’s population II stars. But it is so metal-poor that it starts to give us hope that maybe we’ll get lucky and – while there’s not anything in the nearby universe that is pristine material just starting to form stars – maybe we’re going to be able to find some lensed system from the first billion years of the universe that we’re able to start catching the light of those first supernovae.
Fraser Cain: So, then I have a two-question. I got to remember to bring up the other thing before we end the show, but anyway – So, first let’s talk about trying to observe them. So, you mentioned that they – even though these stars are ludicrously bright, even though their supernova are brighter probably than any supernova we’ve ever seen – they are cloaked in the fog of the early universe and will be difficult to see both their existence, but also their death.
Dr. Pamela Gay: Yes.
Fraser Cain: So, how could we theoretically see them?
Dr. Pamela Gay: If they formed in a pristine galaxy that – or a pristine blob of gas that managed to escape the first round of star formation like a blob of cookie dough without chocolate chips that escaped onto the counter. That escaped gas is probably the best hope we have of seeing these things. Now, the other problem that we’re dealing with is – if you go back to some of the earliest episodes of this show – we talked about the missing G dwarf problem, this idea that low-mass stars have the capacity to live longer than our universe has been around. So, the very first lower-mass stars to form should still be out there shining.
And this is where we get ourselves into trouble of just how effective was the mixing and how much metal does it take to start forming lower mass stars? And these are things we’re still trying to figure out. So, on one side, you have people looking for the oldest low-mass stars that were the very first low-mass stars to have ever formed. And on the other side, you have people trying to find pristine pockets of gas in dwarf irregular galaxies, in other forms of dwarf galaxies, that just don’t have anything to increase the mass of stars as they form – increase the metallicity of stars as they form.
Fraser Cain: Right, right. Now, you mentioned maybe through lensing.
Dr. Pamela Gay: Yes.
Fraser Cain: So, Hubble never could.
Dr. Pamela Gay: No.
Fraser Cain: But I know that using gravitational lenses in the way that Hubble could see the farthest galaxies, Webb could be able to see the farthest stars.
Dr. Pamela Gay: And this is where – at the time that we’re recording this – we are about a week and a half away from getting the first deluge of science to come from the JWST at the American Astronomical Society meeting.
Fraser Cain: Oh, it’s the JWST meeting. Oh, yeah. I never even thought about that.
Dr. Pamela Gay: Yeah, yeah.
Fraser Cain: You’re right. This is gonna be chock-o-block, isn’t it?
Dr. Pamela Gay: They’re gonna have a whole lot of early results from JWST being announced and I’m kind of afraid that anything I say – other than JWST was specifically built with finding first stars in mind – is gonna be out of date within weeks of this episode going live.
Fraser Cain: Yeah, that’s interesting.
Dr. Pamela Gay: So, stay tuned.
Fraser Cain: We should maybe do in that episode.
Dr. Pamela Gay: We have it scheduled.
Fraser Cain: Oh, it’s already scheduled? Okay.
Dr. Pamela Gay: Yeah, yeah.
Fraser Cain: All right. Yeah, yeah, we’ll do a first science result – first proper science announcements – from JWST. That sounds great. So, what would it take then to build? What kind of instrument could see them directly? Because I know there was a space telescope – the Origins Space Telescope – that was shelved and that was going to be a nine to 12-meter class infrared observatory – essentially a super-duper version of JWST. That was hoped could maybe find evidence of the pop III stars.
Dr. Pamela Gay: Right. So, what we need is something that is capable of seeing the faintest light from dwarf galaxies that are being gravitationally lensed or from galaxies that aren’t yet fully fledged, fully full of light. This goes back to how do galaxies form? We have this notion today that they form both through the massive collapse of giant pockets of gas, but also through smaller pockets that collapse into dwarf systems and then merge together.
Those dwarf systems that have less mass in them will form stars at a slower rate. Big things form faster, small things form slower. By being able to see dwarf systems that are being gravitationally lensed and are super faint and are in the earliest days of the universe so their light is redshifted into the infrared, we can get back about as far as we can get back.
Fraser Cain: Right.
Dr. Pamela Gay: It’s hard. It’s hard.
Fraser Cain: Yeah, yeah. Now when you think about the size of these stars – and we talked about how they don’t seem to form – they probably don’t form black holes, but there’s got to be some kind of link. Could there be some kind of link between these first-generation stars and the supermassive black holes – which are also a mystery – because they don’t seem to be able to form quickly enough to have the mass that they have already in the universe that we see them? Is there some connection between these first-generation stars and these monster black holes?
Dr. Pamela Gay: At a certain level, yes because you’re, again, at this problem of, “If you have an atom –” Technetium is my own personal enemy because in stellar spectrum, technetium it has electrons bouncing around at all of the interesting, visibly apparent in your standard optical telescope colors of light. So, you’re trying to study whatever – small magnesium hydride was what I was working on – whatever small molecular lines or atomic lines and technetium is there going, “Hi. There are a few atoms of me. We’re gonna dominate everything.”
And what’s happening is – as the energy tries to radiate out from the center of the star – it’s absorbed in by all of these different energy levels of the electrons in the technetium and then re-radiated as the electrons jump between energy levels going back down. So, you have this one-two whammy of a whole lot more electrons involved in the energy levels and a whole lot more energy levels increases the ability to re-radiate that energy and this causes a pressure essentially. So, the light goes out, it gets absorbed into these atoms, and that supports the outer layer of the star. If you don’t have all of these energy levels to absorb in the protons, the protons just fly through.
So, this allows giant stars to form. Well, if you’re in a early galaxy and you have collapsing mass that is able to heat up and much more effectively radiate out energy, you can first of all get bigger that way. And then models that look at adding in turbulence to again allow more mass to get down in there than you could through a nice, calm collapse, this one-two punch of lower metallicity and significant turbulence allows you to start getting at supermassive black holes maybe.
Fraser Cain: Right. There’s an interesting experiment you can do talking about turbulence. You can take a bottle of pop – what you may call soda – and you turn it upside down and it glugs out and it’s very slow. But if you give it a spin, then the water pours out because it gets an air hole coming up the middle of this vortex and the thing will just empty in a heartbeat – just boom, completely empty – and so turbulence can have a tremendous effect. So, one idea – if the turbulence models are right and if they do just keep gaining mass forever – is you don’t get the pair-instability supernova. Instead, you just get this direct collapse into a supermassive black hole.
Dr. Pamela Gay: Yeah, yeah.
Fraser Cain: That would be crazy. That’s amazing. Yeah, to think that however many million times the mass of the sun could all collect together into one spot and then just directly turn into a black hole.
Dr. Pamela Gay: And it all comes down to how big were these slight overdensities and under densities of mass in the early universe?
Fraser Cain: Yeah. Wow.
Dr. Pamela Gay: If we had had a different distribution of overdensities, we might have become a universe of nothing but supermassive black holes.
Fraser Cain: Right.
Dr. Pamela Gay: So, there’s your food for thought for the day.
Fraser Cain: I love it. All right. Well, that was fantastic, Pamela. Thank you so much.
Dr. Pamela Gay: Thank you and thank you to all of our patrons out there. We wouldn’t be here without you and this week I want to thank Brian Cagle, David Everson, Bruno Leitz, Alex Raine, and I’m gonna pause and say we now have an add-free distribution of this show on an RS feed through Patreon.
Fraser Cain: Nice.
Dr. Pamela Gay: That you can only get if you’re a Patreon. So, I’m gonna keep going. We’re thanking Michael Prochoda, Burry Gowen, Stephen Veit, Jordan Young, Jeanette Wink, Kevin Lyle, nanoFlipps, Barre Andre Lysvoli, J.F. Rajotte, Venkatesh Chary, Andrew Poelstra, Brian Cagle, David Troug, Aurora Lipper, David, Gerhard Schwarzer, Buzz Parsec, cacoseraph, Laura Kittleson, Robert Palsma, Jack Mudge, Les Howard, Joe Hollstein, Frank Tippin, Gordon Dewis, Alexis, Adam Annis-Brown, Richard Drumm, William Baker, WandererM101, Zero Chill, Felix Gutt, Androsetz or Astrosetz, William Andrews, Gold –
Roland Warmerdam, Jeff Collins, Simon Parton. Kellianne and David Parker, Jeremy Kerwin, Rob Cuffe, Harald Bardenhagen, Matthew Horstman, Alex Cohen, Phillip Walker, marco iarossi, David Gates, Scott Kohn, Scott Bieber, Justin Proctor, Matthias Heyden, Claudia Mastroianni, Kseniya Panfilenko, Daniel Loosli, Jim Schooler, Gregory Singleton, Disasterina, Cooper, Tim Gerrish, Tim McMackin, Jeff Willson, Paul D Disney, Eran Segev, NinjaNick, Kenneth Ryan. And don’t you love that there’s fewer episodes in January and there’s that many more names at the end of the episode?
Fraser Cain: Fantastic. Thank you everyone for supporting the work that we do and we will see all of you next week.
Dr. Pamela Gay: Bye, bye everyone.
Announcer 2: Astronomy Cast is a joint product of Universe Today and the Planetary Science Institute. Astronomy Cast is released under a Creative Commons Attribution license. So, love it, share it, and remix it, but please credit it to our hosts – Fraser Cain and Dr. Pamela Gay. You can get more information on today’s show topic on our website, AstronomyCast.com.
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We've always assumed that we lived in a perfectly normal system with a normal star and normal planets. It's all... normal. But with our modern understanding of billions of stars, just how normal is our Sun, anyway?
Don't ever accuse us of not comprehensively covering every kind of exploding star. This week we gather up all the leftover ways that stars partially or fully explode, or don't. Probably. Enjoy.
You'd think that a white dwarf star is the end of a stellar life. It's all downhill from there. A long, slow cool down towards the end of everything. But in some situations, even dead stars can get exciting again, briefly becoming some of the brightest objects in the Universe. And just maybe, the last exciting thing that ever happens in the Universe.
I’ve got some bad news for you: stars die. At some point in the next few billion years or so, our Sun is going to start heating up, using up all the fuel in its core, and then eventually die, becoming a white dwarf. It will then slowly cool down to the background temperature of the universe, becoming a black dwarf.
White dwarfs are usually about 60% the mass of the Sun, so it was a bit of a surprise when astronomers found one that was almost exactly twice that. What happens when white dwarfs merge? Download MP3| Download Raw Show with Q&A| Show Notes | Transcript Show Notes White Dwarfs: Compact Corpses of Stars (Space.com)White […]
You might be surprised to hear that we've never done an episode of Astronomy Cast featuring Betelgeuse. Well, good news, this is that episode. Let's talk about the star, why it might be dimming, and what could happen if it explodes as a supernova.
Last week we gave you an update on the formation of elements from the Big Bang and in main sequence stars like the Sun. This week, we wrap up with a bang, talking about the death of the most massive stars and how they seed the Universe with heavier elements.
The Universe started out with hydrogen and helium and a few other elements, but all around us, there are other, more proton-rich elements. We believe these heavier elements formed in stars, but which stars? And at what points in their lives? Today we'll update our knowledge with the latest science.
Today, of course, we're going to talk about the announcement from the Event Horizon Telescope and the first photograph of a black hole's event horizon.
We learned how to figure out the ages of objects in the Solar System, now we push out into the deeper Universe. What about stars, galaxies, and even the Universe itself? How old is it?