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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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.
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