Cosmology | Astronomy Cast: Recent Episodes
Cosmology | Astronomy Cast
Astronomers talk about all the amazing discoveries they’re making but sometimes, it turns out, they were wrong. After decades and centuries of discoveries, how have they changed their minds?
This episode was made possible by the following Patreon members:
Jordan Young
Stephen Veit
Jeanette Wink
Siggi Kemmler
Andrew Poelstra
Ed
BogieNet
Brian Cagle
David Truog
Gerhard Schwarzer
David
Nicholas Cunningham
THANK YOU! – Fraser and Dr. Pamela
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How the time flies. It’s been over a year since JWST went operational, with other missions joining the fun. What new insights have we gained about the Universe thanks to these powerful new tools?
Recorded live during the CosmoQuestX 2023 Hangout-a-Thon on November 5.
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One of JWST’s top jobs is to peer deeper into the Universe than ever before, watching as the first galaxies came together. Surprisingly, astronomers found galaxies that seemed much more mature than expected, much earlier than it was believed possible. What’s going on and what does it mean for cosmology?
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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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It’s been over 20 years since astronomers first discovered that the expansion of the Universe is accelerating thanks to dark energy. And in these decades, astronomers still don’t have much evidence for what could be causing the increased expansion rate. Maybe there’s something else going on to explain it.
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Show NotesEscape Velocity Space News (CosmoQuest)
PODCAST: Ep. 4: The Search for Dark Matter (Astronomy Cast)
PODCAST: Ep. 11: A Universe of Dark Energy (Astronomy Cast)
The Dark Energy Survey
The Nancy Grace Roman Space Telescope (NASA JPL)
South Pole Telescope (University of Chicago)
Physical Review Letters (APS)
Hot new early dark energy: Towards a unified dark sector of neutrinos, dark energy and dark matter (Physics Letters B)
Casimir Self-Interaction Energy Density of Quantum Electrodynamic Fields (Physical Review Letters)
Dark matter (CERN)
Dark Energy (Hubblesite)
Doppler Shift (Swinburne University)
Equation of state (cosmology) (Wikipedia)
Hubble’s Exciting Universe: Measuring the Universe’s Expansion Rate (Hubblesite)
Planck (ESA)
WMAP- Content of the Universe (NASA)
Supernovae Were Discovered in all These Galaxies (Universe Today)
What are Cepheid Variables? (Universe Today)
Carnegie Supernova Project II: The Slowest Rising Type Ia Supernova LSQ14fmg and Clues to the Origin of Super-Chandrasekhar/03fg-like Events (The Astrophysical Journal)
Research team discovers unique supernova explosion (Phys.org)
Planck and the cosmic microwave background (ESA)
Hydrogen Epoch of Reionization Array (HERA)
FOLLOW-UP: What is the ‘zero-point energy’ (or ‘vacuum energy’) in quantum physics? Is it really possible that we could harness this energy? (Scientific American)
First principle (Wikipedia)
WMAP Inflation Theory (NASA)
Could a Dark Energy Phase Change Relieve the Hubble Tension? (Universe Today)
Michael S. Turner (University of Chicago)
What is the Casimir effect? (Scientific American)
The Nobel Prize
The Higgs boson (CERN)
Particle Fever (2013) (IMdB)
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TranscriptTranscriptions provided by GMR Transcription Services
Fraser Cain: Astronomy Cast Episode 669, Challenges to Dark Energy. 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, 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 Cosmo Quest. Hey, Pamela, how you doing?
Dr. Pamela Gay: I am doing well. The third episode of our new TV show aired Saturday and we got it to the station 90 minutes before it was due, due to computer crashes, because computers know.
Fraser Cain: Yeah.
Dr. Pamela Gay: But if you haven’t checked it out yet, it’s Escape Velocity Space News. It airs on Now Media and I am gonna be putting together a podcast version and loading that up later today.
Fraser Cain: Congratulations, that’s amazing. It’s been over 20 years since astronomers first discovered that the expansion of the universe is accelerating thanks to dark energy. And in these decades, astronomers still don’t have much evidence for what could be causing the increased expansion rate. Maybe there’s something else going on to explain it.
If you go back into the archive of Astronomy Cast shows, one of the first episodes that we did was Dark Matter and then after that was Dark Energy, like within the teens anyway and we’ve brought it up a couple of times since them, but I had been expecting in the 15 years that we’ve been doing this show that we would have something more to say on the matter. But to be honest, not much has been figured out, apart from some really interesting new surveys, like the Dark Energy Survey Telescope, the development and eventual launch of the Nancy Grace Roman Telescope. We still have no idea what this is.
Dr. Pamela Gay: One of the things that actually caught me by surprise is I was expecting to spend today talking about the new results from the Dark Energy Survey and the South Pole Telescope, and there are actually two really cool papers that have both come out in Phys Rev Letters in the past couple of months that are both clearly the, hi, we’re theorists, we have predictions, there are only two of us on this paper, please give us the Nobel Prize when our predictions prove true.
Fraser Cain: Right.
Dr. Pamela Gay: And so, we may be getting to the point that theorists are starting to figure out how to get a handle on things, and they’re finding answers that may also help confine dark matter, which is kinda cool.
Fraser Cain: Well, that’s great. So, then, I guess, what is the evidence for dark energy?
Dr. Pamela Gay: Basically it comes down to when you measure the distance to a supernova and you measure the rate at which that galaxy is moving away from us using doppler shifts. We find that the universe is actually accelerating over time, which is not something that was in anyone’s predictions but it was in the math in the form of a constant to the equations of state for the universe. When Einstein originally came up with these equations there was an integration factor, when you integrate you have to add a constant, and he assumed that the constant would have a value that caused the universe to be static.
A few years later, Hubble came along, found the universe is expanding. Now we have a constant that makes sense for that. But it turns out that if you have a universe that is accelerating apart, that is a value for the equations of state, and so now what we’re finding is, in order to explain the geometry of our universe, which is flat, flat, flat, very flat, and an accelerating universe, you have to have 70% of the universe made of something that isn’t observable matter, that’s about 4-1/2 percent of the universe, that isn’t dark matter that gets observed through gravitational lensing, gets observed through rotation curves of galaxies, gets observed through the motions of galaxies and clusters, that’s 27-ish percent and instead you have dark energy.
Fraser Cain: So, this measurement really relies on how good the measurements to those type 1A supernovae are.
Dr. Pamela Gay: Yes. And it also comes down to, once we realized, okay, so we have from the Planck Observatory the flat geometry and then you combine it with everything else and you look at the mass density of the universe, the only way to explain the mass density of the universe is to have this extra stuff as well. So, you can get to dark energy from a couple of different ways but to get at the value that we’re seeing, yes, that came very clearly from the 1998 observations that the universe is accelerating with time and its expansion.
Fraser Cain: And we did some coverage on a new database that came out a couple of months ago, where astronomers had gone through and like recalibrated, normalized all the data for about 1,000 total type 1A supernova measurements and if anything, have gotten even more accurate.
Dr. Pamela Gay: Yeah.
Fraser Cain: You overlap the Cepheid variables with type 1A supernovae, the distance ladder is beautiful, the error bars are ever shrinking and the amount of dark energy in the universe is zeroing in on this. They’re really nailing this number.
Dr. Pamela Gay: And one of the wild things about this is we keep trying to find an excuse that maybe further back in the universe these kinds of supernovas, due to the change in the chemistry, would have different properties, and we do keep observationally finding random exceptions. There was a super cool type 1A supernova that went off while inside of another star, which is one way to blow up a white dwarf.
Fraser Cain: You can imagine that would pollute the results a little bit.
Dr. Pamela Gay: Right. But these one-offs that we’re finding are super cool but they are one-offs. The vast majority of the type 1A supernovae are just boring white dwarfs that ate more than they could hold without changing states.
Fraser Cain: Right. And so I guess one possibility is that the type 1A supernovae aren’t the standard candles that astronomers had always believed but the evidence is continuing to build that yes, indeed, they are.
Dr. Pamela Gay: Yeah.
Fraser Cain: Except for these ones where one star blows up from inside another star.
Dr. Pamela Gay: Yeah.
Fraser Cain: Right.
Dr. Pamela Gay: And so, I mean it’s just like saying most human adults are between five foot and six foot, yes, there are people who are only three foot and there are people who are only seven foot, but the vast majority of us are between five and six foot. So, yeah, it’s averages.
Fraser Cain: So, then, let’s talk about some of the largescale surveys that have been developed to try to get to the heart of dark energy. Not necessarily explain it, I guess, but at least to confirm it, map it, try and nail down its parameters.
Dr. Pamela Gay: So, the big one with the obvious name is the Dark Energy Survey, which was done from down in Chile where they observed with extreme sensitivity vast swaths of the sky with the goal of looking to see how the structure of the universe evolved with time. So, the idea here is, we know that the universe started out as pretty much smooth distribution of particles. It wasn’t even anything more fancy than particles initially, with slight over and under densities that were created by soundwaves moving through the early universe.
That mostly smooth distribution that we can measure in the cosmic microwave background, then had to collapse down into galaxies, stars at the smallest scales, but then clusters of galaxies, walls of galaxies, super clusters at the largest scale and it does that over time. And we have models that basically say okay, here is the CMB, here is the modern universe, let’s fill in in between and the Dark Energy Survey was designed to get at the more recent few billion years.
The next survey that is super exciting to look at is HERA, which is being done in the radio, looking at the redshifted 20-centimeter line of cold hydrogen, that the detectors for this, they’re looking at wavelengths of light that instead of being just 20 centimeters are instead many, many feet, so, longer than us. And in these longer wavelengths we are able to start seeing how cold hydrogen was distributed in the early universe, start piecing together how cold gas clumped and then got re-ionized in the era of re-ionization.
And between these different surveys, we’re working our way through measuring what was the structure over time so that we can better confine our models and say, okay, was the amount of dark energy constant over time. Was there some sort of a phase transition? Was there a kick somewhere? And these are the kinds of questions that folks are trying to answer, is what observables can dark energy give us that will help us confine our theories?
Fraser Cain: And so, in addition to the type 1A supernovae measurements, they’re able to now look at these galaxy clusters and then on top of that they’re looking at the concentrations of these regions of hydrogen gas. And so, you’ve got like three independent lines of observation that theoretically should allow you to map out the amount of dark energy.
Dr. Pamela Gay: Yes.
Fraser Cain: And is the assumption that they’re gonna find it? Like I know the Dark Energy Survey is still partway through its survey. You didn’t even mention the Nancy Grace Roman, it’s gonna be launching in 2025, and –.
Dr. Pamela Gay: Well, you don’t count your satellites until they’re orbiting.
Fraser Cain: Fine, fine, okay. Pamela, put your hands over your ears. Audience, the Nancy Grace Roman, one of its main jobs is going to be to characterize dark energy, doing kinda the same thing that the Dark Energy Survey is but from space. So, this is classic, right. Like if you don’t have an easy answer then you build more instruments, more observatories. You keep trying to characterize the nature of the problem, building hypotheses, testing them against your observations, removing bad ideas one after the other and hopefully trying to pin down the final thing. So, we may never know what’s causing dark energy but we’ll have it measured to Six Sigma accuracy.
Dr. Pamela Gay: Well, and the other side of it is the particle physics side. So, we know that dark energy, whether it’s a force, an energy, a field theory, whatever it is, puts into every cubic meter of space basically a proton-ish worth of energy. And so, how do you explain that energy existing? And by better understanding the quantum mechanic side of the universe, the particle physics, the vacuum energy, are sterile neutrinosactually a thing or not, this is another way of coming at the fullness of the universe by looking at the smallest factors inside of it.
Fraser Cain: All right. So, I guess, you found a few papers that have been proposing some alternative explanations that would explain the observations but not necessarily be new energy that’s being injected into every cubic meter of the universe, which I guess sounds satisfying. Like the fact that energy is appearing out of nowhere, that’s unnerving, so what are they proposing?
Dr. Pamela Gay: So, the first paper in here, I have to look at my notes, the first paper came out from Martin Sloth and Florian Niedermann, where they’re looking at new early dark energy. And the idea here is our universe has undergone phased transitions in terms of the energy of the entire universe. So, the first massive phased change occurred in the first fractions of a second, where we essentially went from every basically molecule sized bit of the universe expanding out via inflation, which we also don’t know what is, to be about the size of the observable universe according to some ways of looking at it.
And this massive, fairly instantaneous epic of inflation may have only been one of two phased transitions or there could have been a later phased transition that, if there testable ideas are right, leads through first principles to having a cosmological constant of 72, which is within error bars of what we see for the modern universe, and fixes the discrepancy we see with the old universe.
Fraser Cain: And so, sorry, so like, the idea of inflation –.
Dr. Pamela Gay: Yes.
Fraser Cain: Happening in just the first fraction of the Big Bang was developed I think back in the ’70s –.
Dr. Pamela Gay: Yeah.
Fraser Cain: To help explain a lot of the problems with the Big Bang. Like the Big Bang beautifully explains the universe as we see it today, but there are these flaws in the theory. How can vastly separated parts of the universe be similar temperature, there’s a bunch of these ideas. And so, one of the theories is that, in fact, there was this period of rapid inflation that carried everything away from each other really quickly and then it settled down.
So, I think baked into modern cosmology is already this idea, as you say a phased changed, a dramatic change in the expansion rate of the universe. So, it doesn’t seem that surprising that there could then have been others later on.
Dr. Pamela Gay: Right.
Fraser Cain: So, when would have this other, they’re calling it, what, early, what are they calling it, early –?
Dr. Pamela Gay: They’re calling it new, early dark energy.
Fraser Cain: Dark energy. Right, okay.
Dr. Pamela Gay: So, NEDE is the abbreviation.
Fraser Cain: New early dark energy, right. And so when would this have occurred in the timeline of the universe?
Dr. Pamela Gay: This still would have occurred during what they refer to as the dark times prior to the release of the cosmic microwave background. And it fits in with the way – Michael Turner, who is a prominent cosmologist, now professor emeritus from the University of Chicago, he says there’s basically these three unknown pillars of cosmology, inflation, dark energy which he actually named, dark matter. And so, this looks at that early period, makes some solid predictions for temperature details that we should be able to see with enhanced continuing to look at the cosmic microwave background, which tells us everything apparently.
But it also makes some finite predictions for what kinds of neutrinos should be out there, and what kinds of specific particles we can expect to find, thus, also perhaps explaining dark matter. So, we have one coherent theory spelled out in a letter-sized research article making concrete predictions. It seems good and just needs tested now but it’s not the only one out there.
Fraser Cain: All right. Well, let’s talk about the other one, then.
Dr. Pamela Gay: So, the other one is by Alexander, and I’m going to mispronounce this and I am sorry, this appears to be a Ukrainian last name, Tkatchenko, and the other one is Dmitry Federov. And they look at the vacuum energy of the universe, and vacuum energy is something we know is real because of the Casimir effect, which is just one of the best named effects in particle physics. The dude’s name was Casimir but it just sounds cool to say.
And what the Casimir effect says is if you take two plates that are capable of conducting electrons and you put them extremely close together but you’re not actually running charge through them and they’re not being exposed to any fields, nothing should happen I a vacuum. But the reality is, if you put these two plates just a couple nanometers apart within a vacuum, they will either attract or repel due to the constant creation and destruction of virtual particles that are in their creation and destruction, creating a field. So, if you have a proton spring into existence as a virtual particle between these two plates, that proton has a field and it creates the effect.
Fraser Cain: Right.
Dr. Pamela Gay: And we see this.
Fraser Cain: Right. And if I understand, like the Casimir effect, because the gap is so small the virtual particles of only certain sizes can pop into existence outside or as a field.
Dr. Pamela Gay: Right.
Fraser Cain: Outside the plates and then they are pushing inward, there is essentially a field on the outside and not so much field on the inside and it’s pushing on these plates. And once you move the plates farther and farther apart, now there’s room for the fields to appear both in between the plates and outside the plates.
Dr. Pamela Gay: Yeah.
Fraser Cain: And then that force goes away. And it sort of shows you the presence of this vacuum energy that is everywhere. And it’s been beautifully measured, so no one argues with the existence of vacuum energy. The assumption, though, is that this energy cancels out, goes away very quickly and doesn’t provide any ongoing force to the universe.
Dr. Pamela Gay: And that’s one school of thought. Another school of thought is, no, it’s totally providing dark energy-like forces, but when they do all the maths, they have consistently come up with an amount that is too large by a factor of 10 to the 120 for the theories that I like the best and that are among the prominent theories. And the best case for getting it down has, until this paper as far as I know, been 10 to the 30th. And when you’re off by somewhere between 10 to the 30 and 10 to the 120, it really doesn’t matter.
Fraser Cain: That’s a lot. Yeah.
Dr. Pamela Gay: It’s a lot. And this is where these two researchers, Tkatchenko and Fedorov, they said, well, okay, what if the vacuum energy has a polarizability, that the particles can actually have alignments that affect what can and can’t come into existence and annihilate. And they make again solid predictions that should be testable if we go looking with new technology that we don’t currently have laying around.
And it’s just one of those nice, simple, elegant ideas of we know stuff can be polarized. We know particles can be aligned. What if just the universe as a whole has this polarizability characteristic to it that we just hadn’t been including? And again, with this research, it makes set predictions on what to go look for. It looks at the particles that are out there and says, okay, here is what to see in particular physics and I don’t know which team I’m rooting for more. I like the polarizability one.
Fraser Cain: Why choose?
Dr. Pamela Gay: Well, I mean that’s – it’s two theory papers making predictions. Both of them have only two authors. Both papers are clearly gearing up for a Nobel Prize. It’s always good to cheer for people but I guess I’ll cheer for both.
Fraser Cain: Yeah. When you think about the winning Nobel Prizes, many of them start this way.
Dr. Pamela Gay: Yes.
Fraser Cain: That a theorist puts together a paper and says there should be a particle called the Higgs boson, right, and then 30 years later experimenters are finally able to find it, and this is the same thing. So, I mean I guess if dark energy makes you uncomfortable already –.
Dr. Pamela Gay: This doesn’t help.
Fraser Cain: Buckle up. Yeah.
Dr. Pamela Gay: Yeah.
Fraser Cain: You still got another 30 to 50 years of searching and scanning and trying theories to try and narrow in on an answer to it.
Dr. Pamela Gay: And if you want to get a feel for what it’s like within the field of particle physics to watch people so clearly chasing Nobel Prizes, watch the moving Particle Fever, it is very delightful. It shows the good, the bad and the ugly of scientists being scientists, and just the joy that comes from people getting to see their dreams come true through instrumentation.
Fraser Cain: I will check that out.
Dr. Pamela Gay: It’s really cool.
Fraser Cain: Yeah, that’s awesome. All right. Well, thanks, Pamela. I hope within the lifetime of Astronomy Cast we will do the show we finally know what dark energy is. After we do the show where we say we finally know what dark matter is, we will do both those shows. This is my promise to all of you.
Dr. Pamela Gay: And this is where it’s just sort of like we can hope, and when that finally happens is that when we retire?
Fraser Cain: No, no.
Dr. Pamela Gay: Okay.
Fraser Cain: Because there will be there will be a hundred new mysteries that are even –.
Dr. Pamela Gay: We keep going until we die.
Fraser Cain: Yeah, there will be a hundred new mysteries that are even more complicated and more troubling, so, no, that’s how this whole process works. All right, Pamela, thanks a lot.
Dr. Pamela Gay: Thank you. And thank you to all the patrons out there. I don’t actually have a thing of names, I just discovered, to pull out because it’s the very beginning of the month and the list hasn’t been generated yet but I do want to say thank you to all of you. We have been reading the names of just a subset of you on air, it’s one of the perks associated with the different levels but we love all of you, whether you’re a $1.00 a month contributor or a $100.00 a month contributor. You allow us, through our ongoing efforts, year after year to allow us to pay our humans and keep the show going, and occasionally replace cables from my camera when they die. So, thank you.
Fraser Cain: I will take this opportunity then to sort of mention a trend, a disturbing trend that you who are a fan of educational content should be aware of and that is artificial intelligence generated content.
Dr. Pamela Gay: Yeah.
Fraser Cain: That more and more websites are moving to this model of getting ChatGPT and other artificial intelligence to generate en masse the material and this trend is going to accelerate.
Dr. Pamela Gay: Yeah.
Fraser Cain: And it’s just another career that is gonna be –.
Dr. Pamela Gay: Go away.
Fraser Cain: Go away, sunsetted. The career of the science communicator and that’s because it’s way cheaper to let a large language model generate explainer content. And hopefully, Pamela and I have value and place in this society as more and more of this content shifts into being generated by enormous databases. I know it sounds shocking and surprising but this is where it’s all gonna go and it’s gonna happen startlingly fast. So.
Dr. Pamela Gay: We have had people write in and say, hey, why don’t you switch over to using ChatGPT to generate your scripts.
Fraser Cain: Right.
Dr. Pamela Gay: It’s already people are suggesting it.
Fraser Cain: Yeah, yeah.
Dr. Pamela Gay: And we won’t do that.
Fraser Cain: Yeah. I will get ChatGPT to recommend ideas but I won’t –. See, here’s the key, there are no scripts, that’s the trick.
Dr. Pamela Gay: Right, right.
Fraser Cain: So, how could we have a script if there are no scripts? Smart. Anyway. So, if the work that we’re doing, like if the loss of science communicators at the mainstream media was already troubling to you, now they’re coming for all science communicators. So, if supporting the work that we do is important to you to make sure that we can keep doing the show, paying the people on the team, keeping the servers running, all of that, join our Patreon.
Dr. Pamela Gay: Thank you.
Fraser Cain: Patreon.com/astronomycast. Thanks, everyone, and we’ll see you next week.
Dr. Pamela Gay: Bye-bye.
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Astronomers have made extremely accurate measurements of the expansion rate of the Universe and come up with different results. And the error bars for the observations don’t overlap, so there’s something strange going on. What’s the answer and how can the Crisis in Cosmology be resolved?
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Show NotesSee Comet ZTF (C/2022 E3) Dash Between Big and Little Dippers (Sky & Telescope)
Comet Hale-Bopp (NASA JPL)
Comet Hyakutake (NASA JPL)
Comet NEOWISE, the best comet of 2020 (EarthSky)
Comet McNaught over the Pacific Ocean (ESO)
Hubble Tension Headache: Clashing Measurements Make the Universe’s Expansion a Lingering Mystery (Scientific American)
Hubble telescope refines universe expansion rate mystery (Space.com)
Megaparsec (Swinburne University)
Messier 87 (NASA)
Andromeda galaxy: All you need to know (EarthSky)
Ask Ethan: Is there a better way to measure cosmic time? (BigThink)
Type Ia Supernova (Swinburne University)
How do astronomers measure the brightness of something? (Astrobites)
Luminosity (Swinburne University)
Standard Candle (Swinburne University)
What are Cepheid Variables? (Universe Today)
Gravitational Lensing (Hubblesite)
Dr. Adam Riess (Space Telescope Science Institute)
Astronomical deep-sky photometry and spectroscopy (BBC Sky at Night)
Gaia (ESA)
Baryon Acoustic Oscillations (NASA)
COBE (NASA)
Planck (ESA)
LAMBDA – ΛCDM Model of Cosmology (NASA)
Astronomers Grapple with JWST’s Discovery of Early Galaxies (Scientific American)
How Did Inflation Happen — and Why Do We Care? (Space.com)
The Big Bang (NASA)
IMPROVING MEASUREMENTS OF THE COSMIC EXPANSION WITH GRAVITATIONAL WAVES (LIGO)
Cosmic Inflation Theory Faces Challenges (Scientific American)
Sloan Digital Sky Survey
The Dark Energy Survey
JWST (NASA)
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TranscriptTranscriptions provided by GMR Transcription Services
Fraser Cain: AstronomyCast, Episode 668, “The Crisis in Cosmology.” Welcome to AstronomyCast, 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. I’m Fraser Cain, 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 you doing?
Dr. Pamela Gay: I am doing well. How are you doing?
Fraser Cain: Doing great. Yeah, nothing to report.
Dr. Pamela Gay: That, I think, in 2023, is really the best any of us could ever ask for.
Fraser Cain: Yeah, the weather is fine, the snow is gone, I’m getting out and doing a bunch of hikes and stuff in the nature, even though it’s wintertime, but still, garden’s coming along.
Dr. Pamela Gay: Dang.
Fraser Cain: I saw the comet last night. It sucks, but…
Dr. Pamela Gay: Oh well.
Fraser Cain: Yeah, it’s gotten quite diffuse at this point, so although it’s bigger and brighter, it’s also more of just a cloud.
Dr. Pamela Gay: It’s spread out, so the light from any given place – its surface brightness is really low.
Fraser Cain: That’s right, so you really don’t get that nice, little, tight nucleus with the tail, you just get this – what looks like a little cloud in the sky. But still, it’s easy to find. It’s so easy to find because it was right beside Ursa Minor, right beside the Little Dipper, and then, it’s moving towards Cassiopeia. So, if you have never seen a comet – you can’t see it with your eyes, but you can see it in a pair of binoculars or a small telescope. It’s easy to find, and that’s nice, as opposed to one where it’s in a fairly difficult constellation to discover. But unfortunately, completely inaccessible now to the folks in the Southern Hemisphere, so this one is just for the folks in the north. So, if you haven’t already –
Dr. Pamela Gay: Who do not have cloud like the Midwestern folks in the north.
Fraser Cain: Right, yeah. It’s gonna peak in just a couple of days from now, so now is your chance, and then it’s just gonna get – but it mostly sucks. I always compare comets to Hale-Bopp and Hyakutake, and people are even like, “Oh, didn’t you like Comet NEOWISE?” I’m like, no.
Dr. Pamela Gay: No.
Fraser Cain: No, it sucked. I could see it with my eyes. That does not a good comet… That is necessary – sufficient but not necessary? Anyway, just barely being able to see a comet with the unaided eye does not – you do not declare victory in the comet world. No, you want the one that is gigantic –
Dr. Pamela Gay: The tail.
Fraser Cain: The tail spans multiple handspans across the sky, that you can see it even in light-polluted skies. That’s a comet, and everything else the universe is sending our way right now is mediocre, and I reject them. So, no, NEOWISE sucked, McNaught sucked, this one sucks. We demand better. I will wait, but I’ve been patient for too long. Come on, comet!
Dr. Pamela Gay: I…I can’t argue with that. All of that is true. It’s all true.
Fraser Cain: Yeah. For people who are like, “Oh yeah, Comet NEOWISE was fine,” no, it wasn’t! It wasn’t, and you’re settling. You deserve better. I deserve better. We deserve better comets. The universe can provide it; it’s done it in the past. It’s time to put up or shut up. All right.
Dr. Pamela Gay: Yeah…
Fraser Cain: Astronomers have made extremely accurate measurements of the expansion rate of the universe and come up with different results, and the error bars of the observations don’t overlap, so there’s something strange going on. What’s the answer, and how can the crisis in cosmology be resolved? So, what is the crisis in cosmology?
Dr. Pamela Gay: So, some people call it the Crisis, some people call it the Hubble Tension. A lot of us just put “WTF?” and call it a day. So, what’s happening is before the supernova teams did such an amazing job of measuring the present expansion rate of the universe, we were like, “Nah, the universe is expanding somewhere between 50 kilometers per second per megaparsec to 100 kilometers per second per megaparsec,” and I had so many profs that were like, “Just use 100. It makes the numbers easier.” It was pleasing.
Fraser Cain: Right. Just so people understand this idea, that you take a megaparsec of space, which is about 33 million lightyears of space, and when you think about that, that is the distance between us and faraway galaxies, like Andromeda’s really close. We’re talking about galaxies that are 30 million lightyears away, like M87 is kind of in that – when you think about the supernova image. Every second that goes by, those objects are now 100 kilometers farther apart, or 50 kilometers farther apart.
Dr. Pamela Gay: And it is a function of how far something is away from you, so the further something is away, the faster it appears to be moving away from you. A lot of people use a raisin bread analogy on this because the raisins stay the same size as the bread dough expands, so two raisins that start really close together will end up a little further apart, two raisins that are really far apart initially will end up seriously far apart by the time that bread is done rising.
Fraser Cain: And why is knowing the expansion rate of the universe important?
Dr. Pamela Gay: It’s one of those things that allows us to put together all the rest of our cosmological ideas of how you go from our universe being a single point to expanding out, to forming hydrogen and helium, trace amounts of lithium and beryllium, to – the whole story is tied up, and it slowed down or it sped up, and understanding what rate we’re going now, since there’s no accelerator pedal that we know about, what we see has to be defined by the physics of our universe, and we can start to define all that physics of the universe if we know this one number that refuses to be measured.
Fraser Cain: I apologize, I was off by a factor of 10 there, so, sorry, and you should have caught me – it’s surprising you didn’t – but a megaparsec is 3.3 million lightyears, not 33, so Andromeda, roughly, is in that ballpark range. So, apologies.
Dr. Pamela Gay: Yes. The way I think about it is someone in Andromeda looking back at us would be seeing Neanderthals.
Fraser Cain: Right, but astronomers don’t think in lightyears, they think in megaparsecs, so if I get off by a factor of 10, that’s fine by you because you don’t even think about it, so apologies in –
Dr. Pamela Gay: It’s true.
Fraser Cain: Yeah, the general public thinks in lightyears while astronomers only think in parsecs and megaparsecs, but yeah, so, apologize, let’s continue. So, why – you were discussing why knowing the expansion rate of the universe is important.
Dr. Pamela Gay: It basically just gives us this reference point that we can work all the other maths back from.
Fraser Cain: So, how long the universe has been around for?
Dr. Pamela Gay: How long the universe has been around for, basically –
Fraser Cain: What will happen in the future…?
Dr. Pamela Gay: The one that gets me is by understanding the current expansion rate, we can actually figure how fast the universe went from being a mostly smooth distribution of gases to forming galaxies, to forming galaxy clusters. The rate at which we formed large-scale structure, at a certain level, hinges on how fast our universe is expanding. It’s everything.
Fraser Cain: Right. And so, in the olden days, we used to get “How old is the universe?” and people would say, “Well, it’s kind of somewhere between 10 and 20 billion years old,” and that’s that range of measurement. If you get 50 kilometers per second per megaparsec, you get one age of the universe because you just measure how long the universe is expanding, but if you get 100, you get a different one, and they are very different, and knowing that is important. So, how do astronomers measure the expansion rate of the universe at the close and at the far?
Dr. Pamela Gay: So, there are two totally different suites of mechanisms. The “local time” way of doing it is we look for supernovae, which give off a set amount of light if they’re Type 1A supernovae – explode a white dwarf star, and you get essentially the same explosion over and over and over again, with errors that we’ve discussed in other episodes.
Measure how bright that explosion appears, measure how fast the galaxy the supernova is in is moving, and this tells you the distance using measured brightness and known luminosity, and it tells you the expansion rate by looking at the Doppler shifting. So, we’re literally measuring how much the colors of the different bands of atomic lines have been shifted by the galaxy’s motion, and that gets us a velocity.
Fraser Cain: Right. And so, we have all of these standard candles, from the Cepheid variables, to the supernova, to – I saw a list. There must have been 30 potential standard candles overlapping, going from – some of which are very well known, others of which are poorly known, but you go from local measurements using parallax that overlaps with Cepheid variables that overlaps with Type 1A supernova, and you just get this really beautiful, smooth measurement, and what number did we get from the local methods of measuring the expansion rate of the universe?
Dr. Pamela Gay: So, we’re getting around 70 kilometers per second per megaparsec, and this is using not just supernovae, but as you point out, there’s a bunch of other methods. So, folks are looking at red giants, they’re looking at planetary nebulae, they are looking even at the distant gravitationally lensed galaxies that we’re able to see multiple versions of using crazy geometry when we can see the galaxies’ lenses do the same thing at different times. All these methods are giving us definitely over 70, and narrowing in on 74, so it seems pretty constant.
Fraser Cain: Right, and the error bars are really tightening up. The quality of the observations is exquisite. I talk to a lot of astronomers, and they talk about how good of a job they’ve done with those observations, and they just gush.
Dr. Pamela Gay: The SHOES survey by Adam Reiss – they’re quoting an error of 1.3%, and they are basically going from the nearby Cepheids that they have taken some of the most precise photometry of that anyone has ever taken, then using Gaia parallax data, and then working all the way out. How often does anything in astronomy get done with that level of accuracy? We know this. The local value is basically 74 kilometers per second per megaparsec.
Fraser Cain: Right. And so, let’s go the other end of the range because there is another group of measurements that are taken not locally.
Dr. Pamela Gay: Right, and this is where things are squirrely. In the cosmic microwave background, we see these baryonic oscillations, these soundwaves that move through the early universe, causing slight over- and underdensities, and we can map so beautifully this distribution with our theoretical models, and by combining our understanding of, okay, the universe had this much regular matter, this much dark matter, this much – putting all of these base understandings that we come at from the theory, combining our average temperature information that we got from COBE and other missions, putting it all together, it gets us in the 60s, 68, generally.
Fraser Cain: But the most accurate version of this was the Planck satellite from the European Space Agency.
Dr. Pamela Gay: Right, and this is where it’s important to note the Planck data was used to get at that distribution of baryonic oscillations, and that was used in combination with a mean temperature that they were, in a lot of the papers, referring back to COBE data. So, Planck got us, very specifically, deviations about the mean, and we just fed all the data together in the context of what’s called lambda cold dark matter.
This is a theoretical framework that says that our universe is not just expanding, but it’s accelerating as it expands, that the dark matter, the stuff that we’re not really sure what it is, that may be related to neutrinos in some way – whatever it is, it wasn’t moving extremely fast early in the universe, so that’s where the “cold” part comes in. So, we have lambda, the dark energy, and cold dark matter, two things we have very poor understanding of. When you combine those with the data, it gets you, again, roughly 60 kilometers per second per megaparsec with error bars that don’t overlap.
Fraser Cain: Right, and this is the key. So, you look at the local neighborhood and you get a measurement that’s in the low 70s with very tight error bars, you look at the early universe, you get 68 with very tight error bars. Both are exquisite observations, both are trying to tell you the same thing, and they disagree with one another, and this, at the heart, is the crisis in cosmology.
Dr. Pamela Gay: Correct.
Fraser Cain: So, this is the crisis in cosmology, so what’s the answer?
Dr. Pamela Gay: Well, this is where I personally am a bit excited, and I don’t know how many people are with me on this one because I wasn’t at the meeting, but at the American Astronomical Society meeting, there was a lot of discussion about how JWST images of gravitationally lensed early galaxies appear to be showing from two different studies that have both made it through peer review that there were already well-formed galaxies 350 million years after the Big Bang, and that’s early.
There is other work that is being done that is still going through peer review that is showing there may have already been galaxies – massive ones – at 200 million years after the Big Bang. So, with galaxies forming this early in the history of the universe, it tells us that that model we have, lambda cold dark matter, is off somewhere because while we thought there would be a couple, a few massive galaxies early on, those baryonic oscillations didn’t lead us to believe there would be as many as we are now finding.
And so, we have to figure out a new way to get from mostly smooth universe with the cosmic microwave background to galaxies forming in bigger and probably larger numbers than we anticipated to our present structure, and folks are putting out ideas like maybe there was a bit of leftover inflation, maybe the value of dark energy hasn’t been constant, and all of these different ideas – I don’t think we can really throw anything out yet, and I am the first person to want to throw out ideas.
Fraser Cain: Right. So, the challenge here is that you’ve got – the most obvious possibility is that one or both measurements is incorrect –
Dr. Pamela Gay: Yes.
Fraser Cain: – which is what would be everybody’s first instinct, that someone’s wrong, that one of these measurements is incorrect. But, because of this dichotomy, both measurements have been scrutinized and scrutinized, and teams have gone back, and all they’re doing is narrowing the error bars. They’re not finding a large discrepancy. So, that’s the one that is most likely, and yet, that seems to be less and less of the case, and so, you’re left with the universe –
Dr. Pamela Gay: New physics.
Fraser Cain: New physics, right, that our understanding of Einstein, our understanding of what those acoustic oscillations should be in the cosmic microwave background, is wrong.
Dr. Pamela Gay: And this is where I’m not gonna lay blame on anybody. Relativity seems to work so far, it doesn’t seem to be the problem, but our understanding of the distribution of kinds of matter, the way different forces interplayed, whatever the heck inflation might be – we have no idea what inflation might be – it is somewhere in this physics of how we get from the Big Bang to now that we are missing something, and it’s kind of awesome.
We don’t get a whole lot of surprises anymore, it feels like, some days. We’ve found all the particles in a standard model. We didn’t find any of the particles from supersymmetry. This gives us something new to chase, and the fact that even the folks using gravitational waves to measure distances – they’re still getting the same local universe numbers.
Fraser Cain: And that’s harder to get wrong.
Dr. Pamela Gay: Yeah!
Fraser Cain: I know I’ve talked to some people working in gravitational wave observatories, and I’ve had this conversation, and effectively, the more precise, the more powerful these gravitational wave observatories get, the farther they’re able to see out into the universe. You can rely on their measurements, so it’s another layer of observation, but one that’s very trustworthy, and it only goes so far. It doesn’t take you all the way up to the end of the universe, but maybe some future observation will.
So then, new physics – so, maybe we don’t understand how the early cosmic microwave background worked, maybe we don’t understand how Cepheid variables work, maybe we don’t understand all these different pieces, but there have been a few hints. Maybe Type 1A supernovae aren’t the standard candles that we thought they were.
Dr. Pamela Gay: And this is where there are so many different things that are getting us that local 73-ish that, yeah, I’m happy saying there are discrepancies from one Type 1A supernova to another in weirdo special cases. We’ve got to talk about some of those. If the white dwarf ends up inside of another star, that explosion’s gonna be a bit different, and that happens, but it really seems like there is something about how you get from there – cosmic microwave background – to here – gravitational waves, Cepheids, planetary nebulae, supernovae, all these other mechanisms. There’s something in the science that we have yet to uncover.
Fraser Cain: And then, another possibility is if the rate of expansion of the universe changed. So, perhaps there was a – the model that I’ve heard is this idea of late inflation.
Dr. Pamela Gay: Yeah, that’s the one I was looking at as well, where whatever it was that caused us to initially blow up, there’s a little bit of that left over that caused another kick, but we don’t understand what’s going on there.
Fraser Cain: Right, right. And so, if you had an expansion rate of 74 early on – or, sorry, 68 early on, and then it slowed down, you could get the one that’s today, and that’s even taking into account dark energy. I’m sure people are like, “What about dark energy?” That’s layered on top of this. That’s accounted for. And so, you would have this almost – instead of the universe smoothly applying the accelerator on the gas, it was like putting the accelerator a little harder, and then pulling the foot off the pedal a little bit, and then putting it on harder again, and who knows what kind of shenanigans it got up to in the intervening period? So, what is the way forward at this point? What is the way out of the crisis in cosmology?
Dr. Pamela Gay: We need to basically do a survey of just what was the distribution of galaxies and galaxy clusters in the early universe. We have done a beautiful job, first with the Sloan Digital Sky Survey, doing a volume around our galaxy. Then, with the Dark Energy Survey, we have pushed out even farther in some areas of the sky. With JWST, we’re going to be able to continue pushing the survey of structure size further and further out, watching how the universe goes from being Swiss cheese with giant holes in it to being Swiss cheese with smaller and smaller holes in it –
Fraser Cain: Right.
Dr. Pamela Gay: – and by measuring how that large-scale structure changes over time, that will start to put a different form of constraint on our models. We need to be out there, counting early galaxies.
Fraser Cain: Right, and so, you’ve got this structure of the cosmic microwave background radiation, and the hot spots and cold spots should map to equivalent clusters and distributions of galaxies, and so, you’ll know that this transition from the farthest that you can see to more recent is smooth –
Dr. Pamela Gay: Yes.
Fraser Cain: – and then, that will tell you, and you can keep moving forward at that point, but that’s a much harder observation. Weird as it sounds, the galaxies are much dimmer and harder to spot and map out than the cosmic microwave background radiation, which is everywhere in all directions.
Dr. Pamela Gay: Yeah. More telescopes.
Fraser Cain: Yeah. And then, the other side of that is going farther with gravitational waves, and hopefully, you’ll get to this point where the two overlap, where the gravitational waves reach the cosmic microwave background, or shortly after.
Dr. Pamela Gay: That is technology that someone maybe someday will fund, and we’re at that frustrating point where the next big discovery beyond what we can do with the new, massive radio telescopes that have started to catch star formation at earlier periods, and what we can do with JWST – it’s gonna take multiple nations getting together to build these 30-, 80-, however-many-meter telescopes that are being discussed to be able to look back.
Fraser Cain: All right, place your bets. It’s the close observations are wrong, the CMB observations are wrong, or there’s new physics.
Dr. Pamela Gay: New physics.
Fraser Cain: Really? That’s the most exciting outcome possibility, is new physics, so if that’s true, that would be wonderful.
Dr. Pamela Gay: Or at least a new understanding of that cold dark matter temperature.
Fraser Cain: It would be huge thing, like there was a revision to relativity that nobody saw coming.
Dr. Pamela Gay: So, again, I’m not sure saying a revision to relativity is the right way to say it because I think that what we’re looking at is something coming out of the realm of particle physics, and particle physics and relatively do not talk to one another, and I really think it’s going to be something about how particles interact in different regimes, and whatever the heck this dark energy is that’s gonna be what gets us to the solution to this discrepancy.
Fraser Cain: I think this “crisis” makes it sound like a bad thing, but you talk to astronomers, and they couldn’t be more excited. They’re so happy to not understand something, what was considered to be this bedrock idea, because the problem is bedrock is you get this ossification. Suddenly, you have this space that has opened up, where the solution is in there somewhere, and a lot of interesting ideas and theories, and a lot of brainstorming, and a lot of intellectual power gets to be put onto this problem, and they love it. They love it. So, I feel said that the term “crisis” – because you get a lot of pseudoscientists sort of rolling their eyes at scientists at this thing.
Dr. Pamela Gay: I like “the Hubble Tension.”
Fraser Cain: “Hubble Tension” – yeah, but “Crisis in Cosmology” is a better name, so I’d rather reel them in with “the Crisis in Cosmology,” and then help people understand that, in fact, astronomers couldn’t be more excited and happy to have this opportunity. All right, Pamela, thank you so much.
Dr. Pamela Gay: Thank you, Fraser, and thank you to everyone out there who makes this show possible through your patronage at Patreon.com/AstronomyCast. This week, I would like to thank Camy Raissian, Gabriel Gauffin, Benjamin Davies, Steven Coffey, john öiseth, Arcticfox, Dean, Corinne Dmitruk, Bart Flaherty, The Lonely Sand Person, John Drake, Nate Detwiler, Lew Zealand, Brian Kilby, Naila, The Air Major, Ron Thorrsen, Arthur Latz-Hall, Leigh Harborne, Jason Kardokus, Robert Hundl, Kim Barron, Paul Esposito, Ruben McCarthy, Bob Zatzke, Jordan Turner, Timelord Iroh, Daniel Donaldson, Frank Stuart, Ian Abdilla, and Geoff MacDonald. Thank you all so much for making everything we do possible.
Fraser Cain: Thanks, everyone, we’ll see you next week.
Dr. Pamela Gay: Bye-bye.
Voiceover: AstronomyCast is a joint product of Universe Today and the Planetary Science Institute. AstronomyCast 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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Astronomers came together in January to present their newest research, and not surprisingly, the Winter AAS meeting was heavy on news from JWST. What were some of the new results that were announced?
Download MP3 | Show Notes | Transcript
Show NotesEscape Velocity Space News (CosmoQuest)
NowMedia TV
NowMedia Channel (YouTube)
Roku
First Science Results from JWST (Space Telescope Science Institute)
241st AAS Meeting (American Astronomical Society)
First Images Shared From Webb Telescope Reveal Unseen Universe (ESA Webb)
VIDEO: AAS 241 Press Conference: Building Systems in Our Local Universe (AAS Press Office)
VIDEO: AAS 241 Press Conference: Eyes on Galaxies with JWST (AAS Press Office)
NASA’s Webb Reveals Cosmic Cliffs, Glittering Landscape of Star Birth (NASA)
Close-up of “Proplyds” in the Orion Nebula (Hubblesite)
Herbig-Haro Object (Swinburne University)
Carina Nebula Jets (NIRCam Narrowband Filters) (ESA Webb)
JWST Sees Furious Star Formation in a Stellar Nursery (Universe Today)
The Pillars of Creation (NASA)
NASA’s Webb Takes Star-Filled Portrait of Pillars of Creation (NASA)
The Initial Mass Function (The Center for Astrophysics | Harvard & Smithsonian)
Pleiades – or 7 Sisters – known around the world (EarthSky)
Webb Reveals Shells of Dust Surrounding Brilliant Binary Star System (Webb Telescope)
NASA’s Webb Uncovers New Details in Pandora’s Cluster (NASA)
NASA’s Webb Delivers Deepest Infrared Image of Universe Yet (NASA)
Astronomers Grapple with JWST’s Discovery of Early Galaxies (Scientific American)
Two Remarkably Luminous Galaxy Candidates at z ≈ 10–12 Revealed by JWST (The Astrophysical Journal Letters)
Early Results from GLASS-JWST. III. Galaxy Candidates at z ∼9–15 (The Astrophysical Journal Letters*)
Gravitational Lensing (Hubblesite)
LAMBDA – ΛCDM Model of Cosmology (NASA)
NASA’s Webb Telescope Reveals Links Between Galaxies Near and Far (NASA)
Coelacanth (Smithsonian Ocean)
NASA’s Webb Confirms Its First Exoplanet (Webb Telescope)
NASA’s Webb Reveals an Exoplanet Atmosphere as Never Seen Before (NASA)
New Webb Image Reveals Dusty Disk Like Never Seen Before (NASA)
The Late Heavy Bombardment: A Violent Assault on Young Earth (Space.com)
NASA’s Webb Catches Fiery Hourglass as New Star Forms (NASA)
VIDEO: The Science of the L1527 “Butterfly” with Dr. Karl Stapelfeldt (Weekly Space Hangout)
NASA’s Webb Captures Dying Star’s Final ‘Performance’ in Fine Detail (NASA)
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TranscriptTranscriptions provided by GMR Transcription Services
[Intro Music]
Fraser Cain: AstronomyCast Episode 667: JWST First Science Results. Welcome to AstronomyCast, 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. 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. Hey Pamela, how you doing?
Dr. Pamela Gay: I am doing well. I had a super exciting thing happen on Saturday.
Fraser Cain: What happened?
Dr. Pamela Gay: The very first episode of Escape Velocity Space News aired on NowMedia television. Our new TV show has gone out to the masses, and we’re gonna be releasing the podcast and YouTube versions this week. So, I’m hoping everyone will go check it out.
Fraser Cain: Well, that’s exciting! If you want to watch it on the television, where do you have to live?
Dr. Pamela Gay: So, I can’t keep track of all of the cities they have coverage in. I know that they’re in Houston, I wanna say San Antonio, Atlanta, Mexico City, and there are other cities. But if you go to nowmedia.tv, you can find out all the cities, –
Fraser Cain: Mm-hmm.
Dr. Pamela Gay: – and they also go out on Roku and of course, on their own website.
Fraser Cain: That’s cool. So, if you have a Roku, you can subscribe to the Now –
Dr. Pamela Gay: Yep.
Fraser Cain: – television channel, and then you can watch. Or you can just watch it on YouTube.
Dr. Pamela Gay: Yeah.
Fraser Cain: Right. It’s funny, but like what is a television show in this modern age?
Dr. Pamela Gay: Well, it’s so weird, ‘cause it’s Patreon-funded. When did TV start to be Patreon-funded? But –
Fraser Cain: Mm-hmm.
Dr. Pamela Gay: – this is where we live, people.
Fraser Cain: Yeah. Yeah, exactly. Astronomists came together in January to present their newest research. And not surprisingly, the Winter AAS meeting was heavy on news from the James Webb Space Telescope. What were some of the new results that were announced? Now, you didn’t attend this AAS, did you? You don’t normally do.
Dr. Pamela Gay: Remotely.
Fraser Cain: Yeah.
Dr. Pamela Gay: COVID is still bad enough that going to a 100-person event last weekend was like the limits, and I still –
Fraser Cain: It’s scary!
Dr. Pamela Gay: – was exposed to COVID, but –
Fraser Cain: Yeah.
Dr. Pamela Gay: – same room, different time blocks.
Fraser Cain: Right.
Dr. Pamela Gay: Yeah.
Fraser Cain: But you didn’t get it?
Dr. Pamela Gay: No.
Fraser Cain: Good. Yeah. It’s funny. So, the last time we were together was at the Winter meeting of the AAS in Honolulu in –
Dr. Pamela Gay: Yes.
Fraser Cain: – 2020, and this was about a month and a half, two months into the beginnings of the pandemic. And I think we even had this very conversation.
Dr. Pamela Gay: Yes.
Fraser Cain: But this is probably the last time that we’re gonna be traveling for a while. And true enough, I haven’t been on an airplane since. So, –
Dr. Pamela Gay: Yeah.
Fraser Cain: – 2020, 2021, is it three years now I haven’t been on an airplane?
Dr. Pamela Gay: Yeah.
Fraser Cain: But I’m ready. I’m ready. I’m almost ready to get back on an airplane and start to travel again. But I’ve been busy with the forest. So, I guess what were the big… I guess we’re just gonna dive into this. Let’s talk about this. As I mentioned in my introduction, right? It was JWST news. Why was it so heavy on news from Webb?
Dr. Pamela Gay: Well, it was that sweet spot where folks started getting their data about six months ago. And six months is kind of the minimum amount of time needed for a well-funded research team, especially if there’s a Summer in there, to go from data in hand to analyzed result that’s ready to be presented, and in some cases, published.
Fraser Cain: And so, a lot of the time, from up to this point, the news that we’ve been seeing has been someone from NASA has gone, “Here’s a cool picture!” And posting it on the NASA website with the bare minimum description, or some researchers, or there’s been stuff that’s been publicly available that people are pouring over, because some of the stuff is in open access. But a lot of it is proprietary research, –
Dr. Pamela Gay: Yep.
Fraser Cain: – they’ve booked time on the telescope, they got their data. Only they got it, –
Dr. Pamela Gay: Mm-hmm.
Fraser Cain: – and now they’ve had up to six months to analyze it, process it, and they were able to start explaining it to their cohorts at the American Astronomical Society meeting.
Dr. Pamela Gay: Yes. And the results that came out spanned everything from star formation in a whole variety of star-forming regions to remarkable observations of some of the earliest-detected galaxies in the universe. And it’s hard to even figure out where to start, because really, the science spans the entire gamut of the profession, basically. There were even a couple of planets.
Fraser Cain: Right. So, I mean, were there any large themes?
Dr. Pamela Gay: I think there were two big themes. One was star formation observed with JWST, and the other one was these early galaxies, and do they / don’t they break our understanding of how our universe formed and evolved.
Fraser Cain: All right. Well, let’s go into star formation then.
Dr. Pamela Gay: Yes. So, back in July, we got that amazing – they named it, “Cosmic Cliffs Image” –
Fraser Cain: Mm-hmm.
Dr. Pamela Gay: – of the Carina Nebula, and the set of filters that they turned into that beautiful color image included filters that light couldn’t pass through. So, you have this yellow wall with the blue nebulosity above it. Now, when they instead only look at some of the filters, they’re able to see through that yellow wall to all the star formation that’s going on within. The Carina Nebula is known to be a remarkable star-forming region. There have been papers from Hubble coming out detailing solar system proplyds.
These are the cocoon-y formations where a star is just starting to light up in the core. There have been objects called, “Herbig-Haro” objects that are protostars that as material flows into them, some of it gets ejected then through jets in the Axis of Rotation. There’s been a whole variety of these different, young, active stars detected in the past, but the detections have always been, “We kinda, sorta think we’re seeing this, but we’re not really sure.” Well, when JWST hit the scene, it not only was able to go, “Yes, all of those are real, Herbig-Haro, Herbig-Haro, Young Star, Young Star,” –
Fraser Cain: Mm-hmm.
Dr. Pamela Gay: – identifying all of them. It was able to also identify additional new objects, additional new jets. And the jets in particular are what we’re interested in, because as a molecular cloud like the one that led to all this star formation in Carina, as it fragments and collapses into individual stars, the biggest fragments collapse down fastest. Gravity does that. Biggest stars form first, you get these jets coming out.
Those jets then smush the other fragments around them, thus triggering more and more star formation. Hollowing out nebula over time. This is a stellar feedback mechanism. And well, once you turn off that yellow wall by going to longer wavelengths, you can see the stellar formation and the stellar feedback in action. And Carina was just one example of this. Hubble famously observed the pillars of creation, and that image has been used in just about everything since then.
Fraser Cain: Yeah.
Dr. Pamela Gay: Well, JWST got their own version of that image that we saw last Fall. And yet again, we’re seeing more of this star formation, identifying the details. And this is starting to allow us to get at something I think we’re gonna start hearing more and more about again. And this is what’s called the “Initial Mass Function,” which is the distribution of sizes that stars form in out of different collapsing and fragmenting molecular clouds.
And by looking at all these different systems that have different contents, different masses, and seeing how stars of different masses form in different numbers, it starts to allow us to get down to the population statistics of these regions in ways we couldn’t when we couldn’t look through the gas. So, yay for x-ray vision that’s actually infrared vision.
Fraser Cain: And I think that release was the perfect example of this first initial showoff of a really great picture, but with not a lot of science going –
Dr. Pamela Gay: Right.
Fraser Cain: – on.
Dr. Pamela Gay: There was no science.
Fraser Cain: They were like, “Here…” Well, there was SOME, I mean. But here is the Carina Nebula. Look at these cool cosmic cliffs. And these –
Dr. Pamela Gay: Yeah.
Fraser Cain: – described some of the features, right? You know what you’ve got this. When you think about that picture, you’re seeing the combined stellar wind of all of the stars that have already mostly formed and blown out their neighborhood.
Dr. Pamela Gay: Right.
Fraser Cain: And it’s like this combined wind that they’re creating that is continuing to pile up and blow away this material off into space, and eventually, the whole area will be cleared. We’ll feel a lot more like say, the Pleiades. But –
Dr. Pamela Gay: Yes.
Fraser Cain: – for now, you’ve got the parts that are in Nebula and out of Nebula, and then you got to see a few little knots and regions and stuff. But this time around, now they’ve gone back through and they’ve measured things, and they’re saying like, “Here’s a star, and there’s a star, and here’s the jet.” And then, they’re measuring the amounts and quantities, and they’re also looking at the kinds of chemicals that are piling up. And so, you get this detailed analysis of six months of the astronomers doing their job on what was a beautiful picture. And in many cases, this is probably some of your phone wallpaper right now. But we got the analysis of that picture, –
Dr. Pamela Gay: Yes.
Fraser Cain: – and that for astronomers is really interesting, because no star-forming region has been imaged at this level. And I think like with Hubble, I mean, we have images of Carina Nebula taken by Hubble, and we have images –
Dr. Pamela Gay: Yes.
Fraser Cain: – from the Eagle Nebula. But Hubble has some infrared capability. And so, Webb was able to give far more resolution, and also peer through a lot of the gas and dust that’s obscured to Hubble to see even more features. And so, they’re looking at many new objects that had never been seen before, as well as being able to confirm the objects that Hubble had already seen. So yeah, it’s just amazing research. And that is, I think, just the perfect example of a gorgeous picture, –
Dr. Pamela Gay: Yes.
Fraser Cain: – and now the follow-along science, which is just as interesting to astronomers. And hopefully, to the public.
Dr. Pamela Gay: And with both of these systems, it’s really a matter of looking at the forest, where we’re seeing the entire region of star formation going on. But there were also opportunities where it was able to focus in on not just individual trees, but their leaves, you might say, to carry that analogy far too far.
Fraser Cain: Yeah.
Dr. Pamela Gay: And this is where they have this tremendous image of Wolf-Rayet 140, which is a binary system with a Wolf-Rayet star. It’s about 10 solar masses, and a companion that is an O-type star about 30 solar masses. And these two systems go around each other every 7.9 years. And when they do, it compresses out a shell of material. And so, we’re able to see these individual shells that are getting compressed together through orbital mechanics and gravity playing together as this young star is settling down into its very short life.
It’s these kinds of details that JWST is going to allow us to hopefully start to understand some of the more complex interactions that just haven’t made sense to us as we’d like. We’re seeing the same thing happening with planetary nebula, and other forming stars, and there’s just where do you want to go next?
Fraser Cain: Yeah. All right. So, the next big theme was on the cosmology side. The large-scale –
Dr. Pamela Gay: Yes.
Fraser Cain: – structures in the universe. The things that are most distant.
Dr. Pamela Gay: And at the AAS meeting, the research that we had to look at the published results are based on two different fields that contain galaxy clusters that we’re using to basically fast track us to being able to see the earliest objects in the universe in as little telescope time as possible. These two fields included an Abell cluster, a SMACS cluster. And these two systems, their mass allowed us to see magnified and enhanced amounts of light from galaxies we now have confirmation are 350 and 450 million years after the Big Bang is when we’re seeing them.
Fraser Cain: Yeah.
Dr. Pamela Gay: And they were already formed, and they’re extremely bright. There’s two different competing research teams that published on these. One was led by Rohan Naidu from MIT, and the other one was led by Marco Castellano of the Astronomical Observatory of Rome. And so, when you have two different teams, both conforming the same lookback time for these two systems, that tells us that yes, JWST is seeing things that long ago. And we also see evidence – still needs to be conformed, still needs to go through peer review – potentially of bright galaxies that we’re seeing them as they appear just 200 million years after –
Fraser Cain: Wow!
Dr. Pamela Gay: – the Big Bang. Yeah.
Fraser Cain: And that’s within the capacity probably through gravitational lensing though. It’s gonna take…
Dr. Pamela Gay: Exactly.
Fraser Cain: Yeah. And I think one of the things that’s quite surprising is how well-formed these galaxies are. I know with one piece of research, they saw fairly mature-looking spiral galaxies just –
Dr. Pamela Gay: Yes.
Fraser Cain: – like maybe a billion years after the Big Bang. Galaxies that would look identical to what we have today.
Dr. Pamela Gay: And this is one of the things that the high resolution that JWST is capable of acquiring data at is allowing us to see that there were already not just brighter-than-we-expected galaxies, but bigger-than-we-expected galaxies, and more maturely-formed galaxies. And this is causing a rash of two different kinds of papers. One is saying, “Cosmology is wrong! We don’t –
Fraser Cain: Yeah.
Dr. Pamela Gay: – understand it! JWST overthrows cosmology!”
Fraser Cain: I don’t think that cosmologists are making that claim. I think you have some people who are alternative theorists who have been pushing that diatribe for decades now, and are looking for any little crack in observations to push that narrative.
Dr. Pamela Gay: So, the narrative –
Fraser Cain: No.
Dr. Pamela Gay: – is related the structures of Lambda Cold Dark Matter, where the question is can we understand the ability of Dark Matter, which we don’t fully understand, that is moving fairly slowly – that’s the cold part – to quickly form massive structures. So, on one hand, we have the folks that have been doing some fairly sophisticated computer modeling saying, “Yeah, you can’t get things that big that fast.” Now, on the other hand, you have the star formation people going, “Wait! Wait! Early universe! We don’t understand the first stars.”
So, the argument is actually coming down to were the first stars so much brighter, and was there initial mass function, to bring that phrase back again, was their initial mass function so different from what we’re used to seeing in the modern universe that it was possible to have exceedingly bright, 10 times brighter than expected galaxies within those first few hundred million years, or is there something in our understanding of how the early universe like molecular clouds fragmented and collapsed? Which of those two things –
Fraser Cain: Mm-hmm.
Dr. Pamela Gay: – or both is where the struggle is? My personal feeling is that we don’t have a good understanding of the initial mass function of the early universe because you only had Hydrogen and Helium. And we know that the initial mass function is strongly related to the melodicity of stars. So, I’m leaning that the majority of the problem is going to be on stars were just brighter back then, and we’re still understanding that.
Fraser Cain: One of the observations that I really enjoyed from this round of press releases was the imaging of objects that looked like green pea galaxies. And these were a finding by a team of – was it Galaxy Zoo? Anyway…
Dr. Pamela Gay: It was Galaxy Zoo. Yeah.
Fraser Cain: Yeah. Found these weird galaxies that are green pea galaxies. And so, they’re mashed together. And you’re seeing the light coming, the collective light from all of the ionized gas in the galaxy. There’s so much ionized gas in the galaxy that it’s just glowing in the ultraviolet, and it appeared green in the images. It’s not that it’s actually green. And JWST was able to find examples of these galaxies early, early on in the universe. And although the wavelengths were pushed into –
Dr. Pamela Gay: Shifted.
Fraser Cain: – the infrared, –
Dr. Pamela Gay: Right.
Fraser Cain: – by all means, they matched these green pea galaxies. And so, what’s exciting about that is you get this connection. You got these things that are very close at hand, and are relatively easy to study, and you’ve got a confirmation that these things are very similar to the things that we saw at the beginning of the universe. And so, you can study the ones that are nearby.
They’re easy to get your hands on, and know that you’re looking at something that is kind of primordial. It’s like people pulling up a coelacanth from the bottom of the ocean, this primordial fish, and knowing that this thing has been around for this long. You can study an alligator, or a crocodile, and know that a version of this has been around for hundreds of millions of years. And I really enjoyed that story, and sort of what the implications were.
Dr. Pamela Gay: I’m really enjoying the fact that as we’re able to see better and better in the infrared, we’re able to see that the expansion of the universe has just taken things that are familiar in the ultraviolet, in the modern universe, and shifted them. So, in the Middle Ages, they were optical-colored. Hubble showed them to us.
And now, we’re seeing the exact same objects from early in the universe that are shifted all the way into the infrared, and this confirms to us that while so many things have completely changed, the melodicity content of the universe, the number of heavy atoms, essentially, the basic physics of how things turn on, how they form, what they look like is the same at every single epic, except for maybe that very first epic, ‘cause there was only hydrogen and helium.
Fraser Cain: Now, did we get any planetary news?
Dr. Pamela Gay: There was. So, JWST was able to confirm a test source. It had been seen as two rough transits. Previously, it was seen again by JWST, and with JWST’s abilities, they were like, “Yes, this is a planet.” And there was another world that originally, they thought maybe this isn’t a planet, because there was a double eclipse. And the thinking initially was that it was a sun-like star, and a Jupiter-like planet, and with that size of a planet, you shouldn’t be seeing both kinds of dips.
Fraser Cain: Mm-hmm.
Dr. Pamela Gay: But then, they redid some of the star’s physics, and they were able to figure out, “No, wait. This is an object that the star is actually significantly bigger, significantly hotter, and yes, that is also a planet.” So, we’re at the finding planets, we are at the – they are starting to look at atmospheres, they’re still in the stages of eliminating stuff that they don’t see, but getting down to the stuff we’re interested in, like Carbon Dioxide is going to take a bit longer, just because it’s harder to observe, it’s deeper down in the atmospheres.
Fraser Cain: And there was another image. And this isn’t exactly planets. I guess it kind of is. But it was a picture taken by JWST of this fairly famous, newly-forming planetary system called AU Microscopii. And the star system is fairly new. And it’s relatively close, and it’s seen edge-on. But what was cool was you got a chance to see the coronagraph from JWST in operation. And so, it was blocking out the light from the star, and you could see the protoplanetary disc surrounding it.
And astronomers have already found multiple planets in this disc. And so, you’re seeing the left-over planetesimals that are all crashing into each other, and creating this rubble area around the star that is probably still causing mayhem. So, we think back to the early age of the solar system with the late heavy bombardment period, you’ve got that rough period that these planets are going through right now in this nearby star system. And it’s an amazing picture, just to see the star is gone, and then –
Dr. Pamela Gay: Yeah.
Fraser Cain: – the fainter objects around it are revealed. So, very cool.
Dr. Pamela Gay: And my favorite star – and I have to look at its license plate every time – it’s a star in Taurus L1527. And this is one that you interviewed the scientists who worked on it over on the weekly space hangout. And it’s a fan-like structure coming out from this little, tiny, dark line of a disc in the center that has a young star in the very center. And the light coming out in cones just like a flashlight beam into a dust storm allows you to see all the structure of the gas around this young solar system. And I just love the ability that we’re finding with JWST to make out the fine structure.
Fraser Cain: Mm-hmm.
Dr. Pamela Gay: A bunch of new work on the southern ring nebula is showing very similar, “Okay, let’s turn on just this one neuroband filter. Okay, so we see the hot gas in the center. Now, let’s turn on this other filter. Okay, now we see all of this filigreed ring structure including planetary nebula formed through the basically exhalation of the atmosphere of a star into the surrounding space, and in the outskirts of this, you start to see faint, individual rings from when the material was getting blasted off of this young, white Dwarf.
Fraser Cain: Very cool. All right. We’re gonna have to wait another six months for the next big AAS meeting, and then I’m sure we will see another, probably even more comprehensive list of stories coming out of JWST. Thanks, Pamela!
Dr. Pamela Gay: Thank you so much! And thank you to all of our audience members who support us through patreon.com/astronomycast. This week, I would like to thank by name, Michelle Cullen, Dean McDaniel, Scott Briggs, J. AlexAnderson, Micheal Regan, Benjamin Carryer, Matt Rucker, Peter, Abraham Cottrill, Schercm, Jim McGihon, Frode… he gave me pronunciations that include a character. I don’t know what it means.
Fraser Cain: That’s not helpful!
Dr. Pamela Gay: Okay. Frode, I’m gonna figure this out. Frode Tennebo, Philip Grand, Mark Steven Rasnake, Anitusar, Brent Kreinop, Father Prax, Dwight Illk, Bruce Amazeen, Gfour184, Dustin A Ruoff, Planetar, Alex Raine, Glenn McDavid, Andrew Stephenson, Paul L Hayden, James Rodger, Sean Martz, Cemanski, The Mysterious Mark, Karthik Venkatramen, Sam Brooks and his Mom. Thank you all so much, and thank you to all of you who are putting in pronunciation guides, and if you’re a human whose name I continue to mispronounce, I’ll look up that letter that was deeply mysterious. Thank you.
Fraser Cain: All right. We’ll see you next week!
Dr. Pamela Gay: Buh-bye! AstronomyCast is a joint product of Universe Today and the Planetary Science Institute. AstronomyCast is released under a creative commons attribution license. So, love it, share it, and remix it. But please, credit it to our hosts, Frasier Cain and Dr. Pamela Gay. You can get more information on today’s show topic on our website, AstronomyCast.com. This episode was brought to you thanks to our generous patrons on Patreon.
If you want to help keep this show going, please consider joining our community at patreon.com/astronomycast. Not only do you help us pay our producers a fair wage, you will also get special access to content right in your inbox, and invites to online events. We are so grateful to all of you who have joined our Patreon community already. Anyways, keep looking up! This has been AstronomyCast!
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The Cosmic Microwave Background Radiation tells us so much about the Universe. After that era, the Universe went dark. Then, as gas pulled together into the first stars and eventually galaxies, light returned, beginning the Age of Reionization.
Download MP3 | Show Notes | Transcript
Show Notes241st AAS Meeting (AAS)
JWST (NASA)
Hubble Space Telescope
What is the Cosmic Microwave Background? (Universe Today)
Epoch of Reionisation (MWA Telescope)
What Is the Big Bang? (NASA Space Place)
What are photons? (Live Science)
How the Cosmic Dark Ages Snuffed Out All Light (Quanta Magazine)
Energy Levels of Electrons (SDSS)
Ionization (Energy Education)
Population III stars: The Universe’s ultimate reclusive pop stars (KIPAC)
Dwarf Galaxy (ESA/Hubble)
The Pillars of Creation (NASA)
Spitzer Space Telescope views cosmic bubbles in infrared (BBC Sky at Night)
Messier 42 (The Orion Nebula) (NASA)
Quasar (ESA/Hubble)
What is ‘red shift’? (ESA)
What is Gravitational Lensing? (CFHTLens)
Quasars, the Lyman Alpha Forest, and the Reionization of the Universe (Astrobites)
Lyman-alpha_line (ChemEurope)
Astrophysical Classics: Neutral Hydrogen in the Universe, Part 2 (Astrobites)
Peter Gunn (TV Series 1958–1961) (IMdB)
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TranscriptTranscriptions provided by GMR Transcription Services
Fraser: AstronomyCast, Episode 665, “The Age of Reionization.” Welcome to AstronomyCast, your weekly facts-based journey through the cosmos, where we help you to understand not only what we know, but how we know what we know. I’m Fraser Cain, publisher of Universe Today. With me is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of Cosmo Quest. Hey, Pamela, how you doing?
Dr. Gay: I’m doing well. Right now, the American Astronomical Society meeting is taking place in Seattle, and I was watching the beginning of a press conference earlier before we went live, and there is so much JWST science that’s going to come out this week. It’s tasty, awesome goodness.
Fraser: Yeah. I got up early, got as much of my news organized and out of the way because I just needed to be prepared for the ongoing tidal wave –
Dr. Gay: Onslaught?
Fraser: The onslaught of news, and normally, when the astronomy panels come out, there’s a few interesting takeaways, but I can go a day without saying, “Okay, that’s really interesting and we should cover that” during the AAS, so I’ll do a couple, but I’m sure this one – each one is gonna be superlative, right? This is gonna be the most of this, and most extreme that, and the first time we’ve ever seen this, and this theory’s been overturned. It’s gonna be a monumental week in astronomy and science, the first time astronomers have got a chance to use JWST, and they are going to run with it.
Dr. Gay: Yeah, and we’re looking at a couple of decades of this, and what I’m also enjoying is there are some hints coming out that it is being considered if they can reboost HST to allow it to keep working for a little bit longer, so we might be looking at this nice era of having good coverage from slightly into the ultraviolet all the way into the far infrared-ish – not too far, because they don’t have a lot of coolant – but it’s a good age for discovery.
Fraser: The cosmic microwave background radiation tells us so much about the universe, but after that era, the universe went dark. Then, as gas pulled together into the first stars and eventually galaxies, light returned, beginning the age of reionization. I’ve always had a really hard time wrapping my mind around those early phases, from the cosmic microwave background, to the dark ages, to the age of reionization. So, can you explain that process for everybody, and I will finally get it into my head?
Dr. Gay: I can try. So, as the story goes, universe formed, there was massive heat and energy, and for the tiniest bit of time, the universe didn’t have any stuff in it, but as it expanded and cooled, expanded and cooled, particles came into existence, and at a point about 370,000 years after the formation of the universe, things cooled enough that all of the previously free-flying electrons were able to find a hydrogen, or helium, or maybe, if they were lucky, a lithium or beryllium atom to glom onto, and this process of the electrons joining in with the atomic nuclei allowed the photons that previously had tried to go somewhere and then gotten absorbed, and tried to go somewhere and gotten absorbed, allowed them to finally just fly free.
And so, this moment of the universe cooling enough that atoms could form and photons could fly free is the moment the cosmic microwave background was formed.
Fraser: So sorry, before we move on, I just wanna sort of put a couple of other notes on that. So, the first thing is if you could stand there when these electrons – sorry, when these photons are first trying to fly around, what would it look like? What color would it be?
Dr. Gay: The best way to think of it that I have is you’re gonna have all the colors, first of all, because this is just continuum radiation, and it’s super hot, so, peaking in the ultraviolet, and at the moment that this occurred, it would be kind of like turning off a neon light or a fluorescent light, where you go from having light coming out, but not getting anywhere, so you’re standing there, and the photons that are lucky enough to have been created right beside your eyeballs go into your eyeballs, but the light itself can’t really get anywhere. It’s trapped in this stuff, so it’s like being inside the neon light.
Fraser: Right. And then, the other thing is – you described it – again, it’s like turning off a neon light, but it wasn’t instantaneous.
Dr. Gay: No.
Fraser: It was a gradual process to go from no light can escape to now, light gets to move for a centimeter, to now, it gets to move for a meter, now, it gets to move for a kilometer, and eventually, it got to move for lightyears.
Dr. Gay: And it’s unclear how fast that process happened. It was something where areas of the universe that had a higher density – well, they also had a higher temperature, and areas that had a lower density had a lower temperature, and those lower-temperature regions were the first to be able to go, “Hi, here’s the cosmic microwave background.”
Now, the thing that always gets me is we talk about how the universe was opaque when all these neutral atoms were formed, but we also say this in the same breath that we say the cosmic microwave background was released, which, clearly, we can see. So, how is it that we’re seeing the cosmic microwave background if we now have an opaque, completely neutral universe? And the answer to that is that for the most part, the cosmic microwave background just passes straight through because of its wavelength, which is a bit confusing.
Fraser: Oh, okay. So, it was a wavelength of light, kind of reddish. I always describe it like the surface of a red giant star, that that wavelength was the one that could actually make it out further into the universe than other wavelengths, and so, we see – if you red-shift the cosmic microwave background all the way – right now, it’s microwave, but if you red-shift it all the way back to the beginning of the universe, it’s roughly the surface of Betelgeuse.
Dr. Gay: And so, this light is able to – for the most part – make it through, but what’s cool is we’re finally starting to be able to detect the early moments in our universe where the universe still had pockets of neutral gas, and these pockets of neutral gas are actually causing defects – irregularities – in the cosmic microwave background, so we can see the epic of reionization and before it using the irregularities in the cosmic microwave background.
Fraser: And so, this pushed into the dark ages?
Dr. Gay: Yes.
Fraser: And so, why were the dark ages dark?
Dr. Gay: Well, there was nothing giving off light. So, you have two different problems going on. First of all, you have no stars, you have no galaxies, you got nothing, and the other thing is you have a cloud of fairly dense neutral hydrogen and helium, and that’s gonna absorb light that’s coming at it once there is light. So, you start off with the dark ages, as there’s just nothing giving off light. So, then, stars start to form, galaxies start to form, and the first ones forming are having some of their light absorbed, and what’s cool is we’re using this absorption of light as seen in distant quasars to start pinpointing the moment in history that reionization occurred.
Fraser: All right, so, give us the physics description of what ionization is sort of as it relates to star stuff.
Dr. Gay: All right. So, you have your hydrogen nuclei. It has a proton, some number of neutrons, depending on what version of hydrogen it is, and a happy little electron if it’s neutral, and that electron has certain allowed energy levels. These allowed energy levels mean that if a photon hits the electron, only if the photon has the right energy level to allow it to jump between the different levels will that electron move. It can be thought of as if you’re on a stairwell, you’re either on step one or step two, you can’t be on step one and a half unless you have antigravity boots, in which case we’ve broken the analogy.
Now, photons come along, and if they have just the right energy level, that electron that absorbs the photon is going to jump to a higher energy level, and if the photon has a high enough energy, that electron’s just gonna go away. No more electron. And, it’s that process of removing an electron that’s called ionization.
Now, with hydrogen, you only have one electron to get rid of. With helium, you have two to try and get rid of that are in their own little energy levels, and so, you need more energy to get rid of both of them, and as you have more and more complex atoms, you can have something that’s singly ionized – that means you got rid of one of its electrons. You can have something that’s doubly ionized – you’ve gotten rid of two of its electrons. And, if you have a fully ionized iron, it’s had a really bad day.
Fraser: Right, with shell after shell of ionized electrons. So, the point being that the electrons are no longer in place around the nucleus, they are free-flowing –
Dr. Gay: Yes.
Fraser: – around, and it’s when – and so, that is ionized, and when the electrons pair up with the nucleus to form more, I don’t know, stable atoms, but anyway –
Dr. Gay: Neutral. They’re electrically neutral.
Fraser: Neutral, yeah. Right. And they are no longer ionized.
Dr. Gay: Yes.
Fraser: So, we’ve got these newly forming – we’ve got all this neutral hydrogen that is left over. So, in other words, the universe was ionized. Then, it became unionized because it had cooled down, and you’ve got all this – just a soup of hydrogen –
Dr. Gay: Yes.
Fraser: – neutral hydrogen, where you’ve got hydrogen with its electron, and then, they collapse together in these star-forming processes to form these stars. They heat up, and then they ionize their surroundings.
Dr. Gay: So, this is where it gets super cool. Pop III stars, which we talked about in the last episode – really, really big. And their high-energy photons have an easy time escaping from the core because there’s no heavy elements in the atmosphere of the star to absorb out those high-energy photons and then rerelease them as lower-energy photons. So, we have Population III stars forming. They are giving off ultraviolet and even higher-energy ionizing radiation.
So, we have Population III stars giving off all of this radiation, and this is where dwarf galaxies finally get to do something awesome. Where you have massive galaxies – massive galaxies are gonna have a whole lot of dense, neutral gas around them because more gas to form more galaxy, essentially. The little tiny dwarf galaxies don’t have as much stuff around them, so the stars inside of them are able to give off this ionizing radiation that can escape in much larger amounts.
Fifty percent of the ionizing radiation in a dwarf galaxy is able to escape the dwarf galaxy, and this light is going to ionize a larger and larger bubble, first around each star, then those bubbles will merge, and then around the galaxy, and now you have all these little dwarf galaxies that are just ionizing a Swiss cheese of growing bubbles of no-longer-neutral gas.
Fraser: So, are there some examples of a very similar situation happening in the universe today? I think about the bubbles in the Pillars of Creation. Is that the same kind of thing, where you’ve got this young, hot star that is blowing up this cavity and ionizing the gas around it?
Dr. Gay: It’s a very similar physical process. The science is the science. So, when you have a star-forming system, you have a giant molecular cloud. First of all, you’re not really going to have molecules, other than H2, in the early universe, so you have a giant molecular cloud of all sorts of different gases, and as it collapses down and fragments, these different fragments are going to form stars that are able to blow bubbles around them, including H2 regions, which is the ionized gas around these young stars.
So, you have the same physics, it’s just much more interesting because you’re throwing in molecules that can now emit their own colors of light, allowing us to peer through the gas and dust using radio and infrared telescopes.
Fraser: And so, once again, if you could be there, standing in space a safe distance or maybe an invulnerable distance from the star – we talked about this last week, these gigantic stars at the very edge of what is possible for a star – what would you see?
Dr. Gay: This would be a case of if you were able to fully protect yourself, it would be very much like being underwater, where your headlight – or in a fog cloud, where your headlight allows you to see a certain distance around you, but beyond that, it’s just opaque. So, as you’re near that one just-formed, starting-to-ionize-the-space-around-it star, you have this place where all of the ionizing radiation has been absorbed and done its job, and beyond it, it’s just opaque gas, and you have a wall.
Fraser: Wow! And it would be – the star would have probably – its stellar winds would probably be off the charts, and so, it would have cleared out any additional materials. You’d have this empty space, and then, whatever distance where the edge of the bubble was forming, you would have this reionized gas in this giant sphere around the star, and if you could somehow navigate, you would see them – these blobs of hydrogen with little gaps inside of them where the stars were forming.
Dr. Gay: And what starts to get super cool to imagine is if you’re hanging out in one of these bubbles – and this would require time travel because there weren’t enough heavy atoms to make anything resembling a civilization, so if you time-traveled into one of these bubbles, it would eventually merge with another bubble, so you’d have this window into another area that you could see into that was ionized, and over time, these bubbles would essentially merge with one another, creating a sphere filled with stars, just like when you look at some star-forming regions, you can see that central region – I’m thinking of the Omega Nebula here – that central region that has been cleared out by the star formation and is still surrounded by gas. No dust back then, no dust.
Fraser: So, how long did this period take, do we think?
Dr. Gay: We’re trying to figure this out, and trying to figure this out is a complicated task on two different fronts. So, on front one, we need to be able to figure out the expansion rate of the universe, so we can translate the red shifts, the amount that the different lines being emitted by atoms have been shifted into years, and we also need to observe.
What I can tell you is the galaxies that have quasars in their hearts that we’ve been able to see in the earliest parts of the universe – they’re giving off extremely bright light that, as it travels from that quasar towards us, it’s going to encounter pockets of gas along the way, and these pockets of gas represent areas that are eventually going to become star formation, the material around galaxies between here and there, and some of them represent not-yet-ionized clouds of material.
And when we look at galaxies at Z=6, we’re seeing pockets of this material, but when we’re looking at Z=5 point something, they’ve looked at a variety of these systems, and it appears that already, at that point, the universe was fully ionized, so it was a very fast process.
Fraser: Can you translate that for the non – what is a 5.6 or a 6? Because I know 14 is – sorry, 20, 17 – these new ones that are coming out of JWST, these are 300 million years after the Big Bang.
Dr. Gay: Yeah. So, we’re thinking that all of this occurred between 150 million and 1 billion years ago, and trying to figure out exactly when in there it was done – we know it started around 150 million. We know it was done by 1 billion. Where in between those two that it was done, we’re still figuring out.
Fraser: Right. And I guess the process is uneven, that you’ve got different amounts of gas, different strengths of stars, different sized collections, which were probably linked up to overdensities and underdensities in the cosmic microwave background, and so, different parts collected together, heated up, cleared out sooner than others.
Dr. Gay: Exactly, and like I said, the really cool thing is the dwarf galaxies literally got to shine, and it was the area around the biggest galaxies that, because they had so much more material that they had to ionize, the areas around the biggest galaxies took a little bit longer to clear the way.
Fraser: So, what are our tools to perceive this time?
Dr. Gay: Well, the best tool that we have is gravitationally lensed galaxies that exist back behind galaxy clusters, and those galaxy clusters help magnify the amount of light that we’re able to get, and then, we point our infrared telescopes, like JWST, at those gravitationally lensed galaxies from the beginning of the universe, and we look for quasars, and once we find those quasars, we use them to figure out where in the quasar’s history do we see what kinds of material – well, essentially grabbing out the light. For the collections of gas that are more close by, it’s a Lyman-alpha forest, and then we’re looking back at the stuff that just hasn’t ionized yet.
Fraser: So, we’re seeing the light of the quasar through the gravitational lens –
Dr. Gay: Yes.
Fraser: – because only by harnessing the gravitational attraction of an entire galaxy cluster can you make a telescope powerful enough to be able to see this period.
Dr. Gay: Yes.
Fraser: You’re looking at these gravitationally lensed quasars, and are you seeing them – you’re seeing the light from the quasar go through pockets of gas and dust –
Dr. Gay: Yes.
Fraser: – that are in various states of ionization. You mentioned the Lyman forest. What is that?
Dr. Gay: So, what’s happening is you have – the background quasar is giving off light, where Lyman-alpha is one of the easier-to-spot lines of light. Now, that Lyman-alpha gas that, in the emission lines can allow us to figure out where quasars are. Now, the quasars, in addition to having this entire suite of emission and absorption lines, also have the continuum radiation that they’re giving off.
That continuum radiation, as it travels towards us, is going to have the hydrogen gas, pockets of hydrogen gas, absorb out different colors, depending on where in history they are. So, the light that was absorbed out at 2 billion years after the Big Bang by hydrogen gas is going to be red-shifted to be one color, and that is a Lyman-alpha line that has now been red-shifted into a color we can detect, from the ultraviolet into the reds.
Fraser: Right.
Dr. Gay: From a different age, it’s going to have a different wavelength, so we have the continuum radiation from the quasar that is going to have this forest of what was hydrogen Lyman-alpha absorption lines from an entire suite of different points in history where there were clouds of gas located to absorb the light.
Fraser: So, the light from this quasar is going through multiple gas clouds –
Dr. Gay: Yes.
Fraser: – and you’re seeing the forest with all of these trees.
Dr. Gay: Now, those forests that you’re seeing aren’t the not-yet-ionized gas left over from the Big Bang. That actually gets its own name, which, as someone with dyslexia, I have to be careful with because it’s called the Gunn Peterson trough, and my brain has decided it should be the Peter Gunn trough, which would be far more amusing.
Fraser: Right, right.
Dr. Gay: So, the Gunn Peterson trough is this gap that we can see, a literal trough in the light from the most distant quasars, that is there from the neutral gas that wasn’t ionized in the beginning, and this is what we’re desperately looking for using JWST, so that by finding enough far-away quasars with these Gunn Peterson troughs – while Peter Gunn plays in the background – we are able to say, okay, so we’re seeing these troughs in quasars at these specific points in history, and then we don’t see them anymore. That tells us everything was ionized by this point in history.
Fraser: Very cool. And, as we mentioned in the beginning of the show, be prepared. There’s probably gonna be a bunch of news coming out about the age of reionization just in this week’s American Astronomical Society. So, hopefully, now you will be better able to understand it, like me – I think I get it now, so I think we’re all right.
Dr. Gay: I’m so glad. It’s not easy.
Fraser: All right. Well, thanks, Pamela.
Dr. Gay: Thank you, Fraser, and I need to thank our wonderful patrons who are out there supporting this show. You allow us to pay all of our humans and, where needed, provide them with health benefits, and that is kind of awesome.
This week, I would like to thank by name Burry Gowen, Stephen Veit, Jordan Young, Kevin Lyle, Jeanette Wink, nanoFlipps, Børre Andre Lysvoll, Andrew Poelstra, Venkatesh Chary, Brian Cagle, David Truog, Gerhard Schwarzer, Buzz Parsec, Zero Chill, Laura Kittleson, Robert Palsma, Jack Mudge, Les Howard, Adam Annis-Brown, Joe Hollstein, Frank Tippin, Gordon Dewis, Richard Drumm, Alexis, WandererM101, William Baker, Felix Gutt, Astrosetz, William Andrews, Gold, Roland Warmerdam, Jeff Collins, and Simon Parton. And all of you who join our Patreon will have access to an ad-free version of all of our episodes, so if you’re noticing ads in the episodes, go join Patreon.
Fraser: Do it! Join us! Thanks, everyone, and we’ll see you next week.
Dr. Gay: Bye-bye.
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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?
Download MP3 |Show Notes | Transcript
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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Show Notes * Peering toward the Cosmic Dark Ages (Earthsky.org) * Chronology of the universe (Wikipedia) * The Universe’s Dark Ages: How Our Cosmos Survived (Space.com) * Planck pins down the end of the cosmic ‘dark ages’ (Physicsworld.com) * Epoch of Reionization (MIT) * First Light & Reionization (JWST) * LOFAR Radio Array (Main site) * LOFAR (Wikipedia) * Square Kilometre Array (Wikipedia) * The HST Key Project to Measure the Hubble Constant (STSCI)
Transcript
Transcriptions provided by GMR Transcription Services
Fraser: Astronomy Cast, Episode 550, Missing Epochs – Observing the Cosmic Dark Ages. 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, publisher of Universe Today. With me, as always, Dr. Pamela Gay, senior scientist for the Planetary Science Institute and the Director of Cosmo Quest. Hey, Pamela, how are you doing?
Pamela: I’m doing well, Fraser. How are you doing?
Fraser: Good. I hope you had a festive and fun Thanksgiving time with all your friends and/or family.
Pamela: I did Friendsgiving. I was with some good friends of the show. David Joseph Wesley, you did our theme music, I crashed at his house with a bunch of other friends. And oh my goodness, we ate way too much. But we also arted a lot. So you can now find my art up on Society Six. So societysix.com/starstrider. Go get yourself a planet.
Fraser: I still recommend our version of this is Cakesgiving. So we just get cake.
Pamela: I like that idea.
Fraser: Yeah, we just make cake. And so I’m trying to figure out how to turn Christmas into just pie. Piesmas?
Pamela: Rooksandra, whose last name I’m not going to destroy, one of the friends of our show, she, for her Friendsgiving, made a round meatloaf that had layered mashed potatoes and a parsnip puree, bright purple frosting, and then she used other fruits – not fruits, other vegetables, well tomatoes are a fruit, as garnish. And it looked like a cake-cake, but savory.
Fraser: Yeah, shepherd’s cake. As opposed to a shepherd’s pie.
Pamela: Yeah.
Fraser: That’s awesome.
Pamela: This is a thing that I strongly, for your Cakesgiving and perhaps for Christmas, recommend.
Fraser: Yeah. Powerful observatories like Hubble and the Very Large Telescope have pushed our vision billions of light-years into the universe allowing us to see further and further back in time. But there are regions which we still haven’t seen. The Cosmic Dark Ages. What is it gonna take to observe some of these earliest moments in the universe? Are we about to have a conversation with the James Webb space telescope? Maybe? Just like a little bit?
Pamela: No.
Fraser: Just a tiny –
Pamela: No.
Fraser: No, all right. Fine. It’s gonna happen. All right. So the…I’m trying to think of how to set this up for people. So I mean, I guess when we look – I mean, obviously we’re here in the galaxy, we look around, we see the stars, we can see other galaxies, a couple with our unaided eye, maybe two. With powerful telescopes we can see many. But as we go farther and farther, the view just gets dimmer and more red-shifted and there’s less and less that we can see. So how far back and how far away, and I know this is two different things, can we see right now?
Pamela: Answering that with numbers would require me to know the Hubble constant. And we recently did a show that explains why I don’t know the Hubble constant.
Fraser: Yes, nobody does.
Pamela: What I can tell you is we can see the cosmic microwave background radiation, which we believe was released 400,000 years after the Big Bang. So there’s this one epic wall of light that we see in all different directions. And then we start to see things that cropped up a few million years after the Big Bang. And there’s this gap between the release of that cosmic microwave background and that – well, so there’s two gaps. There’s the Big Bang and then 400,000 years later cosmic microwave background was formed. Haven’t seen anything within that first mysterious epoch.
Fraser: And that’ll be the topic for next week’s episode is that first part that we can’t see. The time when the entire universe was like the interior of a star. It’s hard to see.
Pamela: And then we had a second epoch between when the cosmic microwave background was released and when the universe lit up with stars and galaxies. And we’re just starting to be able to get hints of those early days of the universe during a period that we refer to as the Epoch of Reionization or Epoch of Reionization. I don’t care. It’s that time at which the universe again became transparent.
Fraser: So I mean, I’m gonna need a more specific understanding. So I mean, we’ve got the Big Bang, pull universe is very dense, it’s getting less dense over time, it’s cooling down, eventually it cools down to the point that it becomes transparent, that light can finally escape. And we see this as the cosmic microwave background radiation. And the universe was red at that point. And then – but that’s just all of these photons of light that are left over from the universe being this hot star. And then you’ve got all of this hydrogen and helium gas and it is warm because it was kind of like the Big Bang, cooling off from the Big Bang, able to give off this light. And so then it kept cooling down?
Pamela: So let’s unpack this a little bit.
Fraser: Yeah, yeah. I mean, there’s a bunch of little phases in this idea of reionization and [inaudible] [00:06:09] lit up again. Yeah, so take us very carefully from – everyone understands cosmic microwave background. Let’s move forward from there to what we can see again so we can understand that missing part.
Pamela: So in the moment before the release of the cosmic microwave background the universe was this hodgepodge of atomic nuclei, of electrons, and of photons. So we had light, we had nuclei, and we had electrons. The universe was ionized. Then that next moment, the electrons glommed onto the nuclei. And when this happened, suddenly there were fewer things for all of that light to be interacting with. And light was able to go from the tiniest of distances that it was able to travel before being absorbed and re-emitted to being able to just keep going until it made it all the way to our detectors.
So in that moment, the universe became a mash of neutral atoms and all the photons that had been previously generated were set free. Now, there weren’t new photons being generated at this point in time because the universe is just like hydrogen, helium, trace amounts of lithium and beryllium sitting there going, hi, we’re atoms. Mostly. This is where we start to get interesting things like the 21-centimeter hydrogen forbidden line. And it wasn’t exactly lighting up the whole darn universe, but it was there, occasionally giving off a photon here, a photon there.
And in addition to that, we also have a universe that isn’t completely smooth. There are places that have higher densities and there are places that have lower densities. And that meant that we had an unequal pull of gravity. And so these higher density regions were able to pull material into them, eventually with some of that material forming high enough densities that nuclear reactions ignited in the cores of the first giant stars. We’re talking stars 30 times the mass of the sun to 300 times the mass of the sun.
Fraser: To tens of thousands of times the mass of the sun maybe. I said maybe.
Pamela: I’m gonna go with hundreds.
Fraser: Yeah, yeah.
Pamela: I’m more comfortable going with hundreds of times the mass of the sun. But when this occurred, the light coming off of these incredibly hot stars, ultraviolet light in a lot of cases, that energy is capable of ionizing all of that hydrogen gas. And taking it from being neutral to being, again, free electrons and free nuclei.
But now the universe is a whole lot larger. It’s also a whole lot cooler. So unlike before the release of the cosmic microwave background, when it was a bad thing to have an ionized universe, the universe has now expanded and cooled and expanded and cooled and expanded and cooled to the point that when we re-ionize it, all we’re doing is making it possible for the light from newly forming galaxies to spread out and be seen. And so it’s a good thing to re-ionize the universe.
Fraser: Right. So let me just make sure I’ve got this straight. So you’ve got the cosmic microwave background and so all this light has been bound up, bouncing around, inside from atom to atom and finally it cools down to the point that this light can just escape. And then the universe goes dark again after that first flash of light goes past everything. And the universe goes dark again and it’s all of this hydrogen and helium. And then this stuff collects into stars, the first monster stars. Those stars give off radiation and that radiation re-ionizes, re-illuminates the clouds of hydrogen gas that were everywhere, creating a time that you can see again.
Pamela: And the first stars probably weren’t alone in doing this illumination, this re-ionization of the universe. We also had at the same time, in the most massive galaxies, turbulent inflow of material that formed super massive black holes as well as the accretion disks around those black holes. And accretion disks, if they’re big enough, if they’re dense enough, if they’re hot enough, can ignite and also give off light. When we’re looking at quasars, when we’re looking at active galaxies, that bright central core, that’s not the black hole. Black holes don’t give off light, people. That’s the accretion disk that’s giving off all that light.
Fraser: Right. And so the part that is the dark ages then, is that time from after the cosmic microwave background was released to before the light from all those first stars started to light up all of the clouds of gas and dust. That was the – or gas. That was the – that’s the dark ages.
Pamela: That’s the dark ages. And then it takes time for those first stars and first galaxies to ionize the entirety of the universe. So you have this period of re-ionization, and we don’t know exactly how long it lasts, during which these first sources of ionizing radiation, bright light, are turning on. And they initially, each star ionizes the bubble around it. And then the bubbles start to overlap. And all of this pushes outward, illuminates outward, and clears up our universe. And exactly how that happens – we’ve got computer models, but seeing it, if something were just on the edge of potentially being able to do.
Fraser: Okay, so what’s it going to take to be able to see that then?
Pamela: Well, if we want to see the 21-centimeter radiation, we need telescopes that can see at some of the longest wavelengths of light. 21-centimeter light in our local galaxy requires a radio telescope. And we’re now looking at light that is red-shifted from the beginning, almost, of the universe into the modern day. We’re looking at like 2-meter-long radiation according to one paper I was looking at.
Fraser: Right. So this is the same thing where, say, the cosmic microwave background today is microwave, several millimeters long. Originally it was red light and it’s – over the expansion of the universe it has been stretched out to be this size. And so this 21-centimeter…this hydrogen radiation that was being emitted at originally 21 centimeters is now meters across. And to have a radio telescope that is capable of detecting that at that level of sensitivity is a pretty hard job.
Pamela: And this is where looking at telescopes like LOFAR, which is being built in northern Europe, looking at the future Square Kilometer Array, these massive new radio arrays that have, in some cases, quite large dishes as well, this is how we’re going – it’s not necessarily large dishes. Let me rephrase that. That have antennas sensitive to the longer wavelengths of light. You start building your antennas fundamentally differently. They’re not just big dishes anymore. When you start looking at things that are this long of wavelength. They start looking more like spiky bits coming up out of a field.
So when you start building larger spiky bits rising up out of a field, this is going to allow us to be sensitive to the extraordinarily faint because 21-centimeter radiation, this is generated by the spin flip within a hydrogen atom. There’s different states for the alignments of the particles within the neutral hydrogen. And when you change that alignment, that’s what gives off the 21-centimeter radiation. This isn’t an electron bouncing between layers, this is simply the atom going, huh, this other state might be a little more stable. I’ll flip. And it’s very rare, it’s very temperature dependent. It only occurs in low density environments where you don’t have collisions taking place.
In order to see that, we need massive arrays with huge collecting area and we need sensitivity to this really long wavelength. But we can do this.
Fraser: I mean, this 21-centimeter is great because it’s just – it shows you where all the gas is and where all the repositories of future star-forming gas is located around the universe. No matter how cold it is, it emits this very specific kind of radiation. And if you can see it, you can map out where all that stuff is. So then we’ve identified this time and it’s the first, what, few million years after the cosmic microwave background was emitted. I guess, what do astronomers wanna know about that time? And how could that then help them better understand the universe?
Pamela: Well, it gets down to constraining factors. We have ideas. We always have ideas. We have these theories about –
Fraser: Simulations.
Pamela: Yeah, we have lots of models, simulations, that describe okay, so this is how the universe started, this is the age of inflation, this is the CMB, then we have gas. And then we start to form galaxies in two different ways, through little tiny things building up and merging, and through giant things turbulently and falling. Stars turn on. We don’t understand these stars at all. These stars were in an icy universe. So we can at least see the Swiss cheese of the universe having bubbles of ionized material getting blown up with the 21-centimeter line.
The next thing that we wanna look at, and this is where your JWST hint came in. The other thing is the first stars that turned on would have been giving off massive amounts of light, specifically in the ultraviolet. And that ultraviolet light gets red-shifted into the infrared which is where we start to see the use of the JWST when and if it ever launches.
Fraser: Yeah. It’ll launch. It’ll launch.
Pamela: I don’t count my telescopes till they’re functional. You know this.
Fraser: I know, I know.
Pamela: And it has the potential to begin to see the ultraviolet light of these early stars in its red-shifted into the infrared form starting to resolve the earliest galaxies. It’s not going to resolve individual stars.
Fraser: Right.
Pamela: But we can start to put together patterns of this is how hot the stars appear by looking at these galaxies and figuring out what kinds of spectral energy distributions, what kinds of distributions of light coming off of different numbers and different temperatures of stars are necessary to reproduce the light we see coming from these earliest galaxies. And that’s kind of what we’re hoping to do to map out these still neutral hydrogen gas by tuning our 21-centimeter detections to ever increasing red shifts and by looking for those first stars by looking in the infrared and seeing what their added up light looks like and how we can match it with our models.
Fraser: Again, I know for you James Webb doesn’t exist, but for me – so a couple of the cool things about James Webb is the Hubble Space Telescope, right now, when they use a gravitational lens – normally Hubble can see out about 5 billion – the light from galaxies that are about 5 billion light-years away if it really tries. But it can go a lot farther than that when they did their Hubble ultra-deep field survey. And they were able to see to just a few hundred million years after the Big Bang. And when they wanna be able to – when the galaxies line up perfectly, then they can see with gravitational lensing they can see some galaxy that’s maybe only 500 million years after the Big Bang.
James Webb will be able to see those anywhere it wants, in any direction, at any time. Just like, do you wanna see galaxies over there that are 500 million years after the Big Bang? No problem. But also –
Pamela: You may have to wait for the Earth and the James Webb to orbit to where it needs to be to not have to look through the sun. But yes.
Fraser: Yes. Yeah, yeah, yeah, yeah, you can look at the stuff in the hemisphere of the sky that you want to today. But then also, you’re gonna get – when it does its deep-field with 100 hours of collecting for each of its filters, then it’s gonna be able to go all the way to 250 million years after the Big Bang, which is farther back than anything has been able to see. So we’re gonna get the James Webb version of the Hubble ultra-deep field. And that is just a mind-bending amount of capability. And yet, as you said earlier, that’s not good enough. That’s not enough to see those first stars. That’s enough to see those first galaxies, but you still can’t see those first stars.
Pamela: And this is where we have to remember that even with the Cepheid Key Project to measure the distances to as many of the nearby galaxies as possible using Cepheid pulsating variable stars, that was not able to see much beyond our local group. We are constrained in what we’re able to see. And an, 8-millimeter, an 8-meter dish isn’t going to get us individual stars at the beginning of the universe kinds of resolutions. I haven’t done the math, but my gut tells me a solar system sized telescope still wouldn’t get us the needed angular resolution to see individual stars at the beginning of the universe.
This is where luckily, by spending so much of our scientific history crippled by tiny telescopes, we’ve gotten really good at figuring out what’s going on in galaxies. But only being able to look at their cumulative light, by sticking an aperture on that whole darn thing and summing it up and figuring out what stars must be there. And this is what we’re gonna have to do to figure out the early universe.
Fraser: So now, have you looked into the Murchison Widefield Array? Is this one the observatories that you were gonna talk about?
Pamela: No, that one’s still new. Yeah, you know the future things better than I do because – so for those of you who are new and don’t understand why I’m so reticent to discuss things that don’t yet exist, LOFAR exists, it’s just getting upgraded. SKA will exist, it’s on the ground, it has precursor projects.
When I was working on my dissertation, I had an x-ray satellite I needed not exist the way it was supposed to after launch. There was an engine failure. And the big telescope I was supposed to use, the Hobby-Eberly, didn’t actually start to fully function until many years after my dissertation was complete. So I ended up using the historic McDonald Observatory telescopes, which while fine, meant that I only did a fine dissertation and I remain bitter.
Fraser: Yeah. So it’s farther along than you might think. The Murchison Widefield Array is in Australia. And it consists – and this is like those spiky things you were talking about. It consists of – the original one is 2,048 radio antennas arranged into 128 tiles. And it was built in 2013. And then the number was doubled to 256. And the goal, as we talked about earlier, is to look for that neutral hydrogen. And then all that data, all those data, is fed into a super computer and then they are crunching the information.
And now they have just done a paper just in the last couple of weeks about what they’ve been able to find. And it looks like – and this is going back to what you said, which is that there is a – you can’t resolve the individual stars, but you can see the collective radiation that is coming from all of them all at the same time. And in this case, they’re looking for this collective signal from the neutral hydrogen that was being released during that period during the dark ages. And so they’re getting a lot closer.
Pamela: And what I’m really enjoying is watching the white papers for the 2020 decadal survey starting to come out where we’re seeing people say we need to pay attention to these longer radiation wavelengths. We need to start thinking about how do we use the 20-centimeter line to explore the earliest parts of the universe. People are starting to get tired of waiting to get more infrared on orbit and saying let’s figure out how to do this from the ground.
And it’s really amazing to see all the science that people are figuring out new ways to do, whether it be through looking more closely at gravitationally lens distant galaxies, whether it be by looking in new pockets of the spectrum that makes it through the atmosphere, or just considering building telescopes, well, on the backside of the moon.
Fraser: Yeah, yeah. Now, did you know that there is now an operational radio telescope on the far side of the moon.
Pamela: China has one, doesn’t it?
Fraser: Yeah, it’s a space-based telescope, but it is in the shadow of the moon, is able to observe from that position.
Pamela: It’s a bit tinier than I think people are thinking. I think a lot of people really want to go and take one of these big old craters, buff out the boulders and other bits and turn it into a radio dish. And one of the really cool things is there’s some research I saw a few years ago coming out of Tennessee, I don’t remember if it was University of Tennessee or Tennessee State, where the composition of standard lunar regolith is such that if you nuke it with microwaves – I’m talking like microwave oven nuking it, like we talk about with food, not like nuclear bombs. Bad use of language on my part. If you microwave it, it will solidify.
So you can take regolith powder, shape it into whatever you want, hit it with the right color of light, and now you have a solid. And this gets talked about in terms of this is a great way to make roads, this is a great way to smooth out areas, make landing pads. It’s also a great way to, well, make the support structure that we build a radio dish onto.
Fraser: But, considering the fact that it’s, say, $50,000.00 per pound to put something onto the moon compared to walking over and just building it here on Earth –
Pamela: I know, but instead of having von Neumann probes, can I just have lunar von Neumann robots that just build things on the moon instead of putting people there?
Fraser: Sure.
Pamela: Okay. I just want lunar factories for building telescopes and stuff.
Fraser: So next week we’re gonna talk about that other period of dark ages, right after the Big Bang, which is also very difficult to study, but there may be some ideas. So, Pamela, do you have some names for us this week?
Pamela: So if you would like to support Fraser, Universe Today on Patreon is a great place to do. If you would like to support my artwork, Starstrider on Patreon is a great place to go. And this show is supported through Astronomy Cast on Patreon. All right. So here are the names for this week. I would like to thank for their patronage, Robert Johnson, Jason Kusterat, Jordan Young, Burry Gowen, Ramji Enamuthu, Andrew Polestra, Brian Cagle, David Truog, The Giant Nothing, Chauncey Wilson, Laura Kittleson, Robert Palsma, Jay Kidd, Corey Davoll, Les Howard, Jos Cunningham, Paul Jarman, Emily Patterson, and Warp Factor Nine.
Fraser: Thank you everybody. We really appreciate it. And we’ll see you next week.
Pamela: You make this possible. Bye-bye.
Female Speaker: Thank you for listening to Astronomy Cast, a nonprofit resource provided by the Planetary Science Institute, Fraser Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at Astronomy Cast. You can email us at info@astronomycast.com, tweet us @AstronomyCast, like us on Facebook, and watch us on YouTube. We record our show live on YouTube every Friday at 3:00 p.m. Eastern, 12:00 p.m. Pacific, or 1900 UTC. Our intro music was provided by David Joseph Wesley, the outro music is by Travis Serle, and the show was edited by Susie Murph.
[End of Audio]
Duration: 30 minutes
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