Ep. 683: Cosmic Dawn

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.


(This is an automatically generated transcript)

Fraser Cain [00:00:49] It’s  Astronomy Cast episode 683 cosmic Dawn. Welcome to Astronomy Cast, a 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 Doctor Pamela Gay, a senior scientist for the Planetary Science Institute and the director of Cosmic Quest. Hey, Pam. How are you doing? 

Pamela Gay [00:02:15] I am doing well. We we are continuing to put out new episodes of our Escape Velocity Space news podcast. So if you want news instead of blasting permanent, you can really listen to it all the time. Glory that is Astronomy Cast. We have a little tiny news show that is out there that I would love you to subscribe to. And it’s just exciting to be building new things. 

Fraser Cain [00:02:41] That’s that’s great. After the cosmic microwave background radiation was released, the universe returned to darkness cloaked in the clouds of primordial hydrogen and helium. Gravity pulled these vast clouds into the first stars and then the first galaxies. This is the cosmic dawn. And t will help us probe this mysterious time in the universe. All right, Pamela, cosmic dawn, put cosmic Dawn in perspective for people, like, talk about the earliest eras of the universe, put them in order. Okay. Of time so that we can figure out where cosmic Dawn fits in. 

Pamela Gay [00:03:19] So we have the much talked about first three minutes way over here off the edge of the screen, during which everything that is and ever will be sprung into existence out of a single point, depending on which theories you follow and the forces separated and clue syntheses happened. And the end of this three minutes, we were left with a universe that consisted of hydrogen, helium, and trace amounts of lithium, beryllium. And it was exceedingly hot, hot to the point that all of the atoms were completely ionized, and it was entirely dense, to the point that a photon trying to go through the universe would pretty much instantaneously get absorbed and readmitted in a new direction. So the universe was hot and opaque and ionized, but it expanded and cooled and expanded and cooled and expanded and cooled until about 400,000 years after that Big bang, it reached the point where it was finally cool enough and not dense enough that the atomic nuclei were able to go electrons, you are mine! And the universe settled out into being a neutral gas, and the photons were like, we’re free and they took off. And we are currently able to see the photons that were released 13.8 billion years ago, hitting our eyeballs from all directions. They’re not actually visible to our eyeballs hitting our microwave detectors, which we used to see them from all directions, and we could go anywhere in the universe and we’d be able to see that sphere. It would look different of light that was emitted in all directions simultaneously. At that point. 

Fraser Cain [00:05:15] The analogy that I always that feels really comfortable for me is when you go outside and you look up on a sort of a misty night, or if there’s like some high atmospheric clouds and you can see this ring around the moon. Yeah. And that ring and if you move, you walk 20m to the side. You still see a ring around the moon. And the ring that you’re seeing literally at every moment is a brand new ring that is generated by the light coming from the moon, refracting through ice crystals and making their way down to your eyeballs. And it is different photons every time. And it’s different. Ice crystals every time. Same moon, but different, different different photons coming from the moon and different ice crystals that the light is passing through. And yet you’re constantly seeing this ring around the moon as if it was always there. But it is being. And so the cosmic microwave background is the same thing you are. You’re looking the space. You are seeing the birth cry of the universe, but it’s a completely different region of space that’s a little bit farther away. Every second that goes by, one new part of space is releasing its photons at you and you’re seeing them. And so you’re always seeing this same time in the universe, even though it’s a different place in the universe, because it’s farther away. 

Pamela Gay [00:06:36] Yeah. And and we could go on for episode after episode after episode just talking about the cosmic microwave background. But that is not why we are here today. It is awesome. All hail! The amazing science that comes from the CMB. Yeah. 

Fraser Cain [00:06:51] Then. And like this. This is always a risk when we talk about the CMB is because we could just rabbit hole. It’s unintentionally. It’s been two hours talking about CMB. 

Pamela Gay [00:07:00] But we are not going. 

Fraser Cain [00:07:01] To we’re not going to focus. We we we are professionals. We picked a topic. We’re going to get to it. So so here it is. You had reached the CMB and the dangerous rut that is the CMB, but you made it through what came next. 

Pamela Gay [00:07:19] The problem is, what comes next is the dark ages of the universe, which is this period of time of which we know almost nothing because it was dark. The Dark Ages is that period of time where the universe’s gases were neutral, hanging out, being a giant cloud, essentially, with a few places that were slightly more dense and few others that were slightly less dense and dark matter. And luckily, there was enough structure in this cloud of material that was the entirety of our universe, that the places that had a little more stuff sucked in. Even more stuff with gravity, in the places that had a little less stuff sat there going, hi, I can hold on to nothing. And they got emptier. And the result of all of this was probably just a few hundred, maybe even just a couple hundred million years after the universe came into existence, the very first stars were able to collapse and the ultraviolet light in particular, that was given off by hot, bright, young, massive stars was able to start re ionizing all of the material that makes up the universe. And there were also supermassive black holes forming and being fed by material falling into them. And that was also giving off ultraviolet light. And so we have this moment where the universe goes from dark, except for the leftover bits of the cosmic microwave background to a universe that begins to have pockets of structure and starts its way on the journey to becoming what we see today. 

Fraser Cain [00:09:15] And another analogy I bet a bunch of these analogies that I’ve worked out, I’ve I’ve, you know, workshopped over decades. Have you ever, like, stood at the top of a mountain and watched fog rolling through an area? Yeah. And and you can see when the fog hits an obstacle, like a Statue of Liberty or a an island, you get this, this clear spot that there’s no fog in at all, and yet there’s fog all around. And so if you’re standing in that clear spot, you look around and the air would be perfectly clear. And then you see this wall of fog. But from above we can see the this gap opened up in the fog. And so imagine that, that those first stars that are forming in this giant fog of material of hydrogen, helium, this cooled down enough to form stars, but is still everywhere blocking all the light. But you get these pockets and the radiation that ultraviolet radiation coming from the stars is blasting open these pockets, and every now and then two pockets merge in. Two stars can see each other for the first time. You’re like, oh, you’re over there. Hi. That’s great. Is that cosmic Dawn? Well, when does it become cosmic? Because again, this is an episode we’ve done first stars in the universe. We could rabbit hole again. Yeah, but I want to make this this distinction. When does cosmic Dawn start? 

Pamela Gay [00:10:42] And cosmic Dawn is really when you go from. Individual little bubbles to the universe is opening up. So think of it as as sunrise is when the day begins. Cosmic dawn is when the transparency begins. And so there is this magical moment that we’re starting to hone in on. It looks like it occurred somewhere between 200 million years and 500 million years after the Big Bang. Where? The the density of the the neutral gas between galaxies between clusters of galaxies had become diffuse enough that you can say the universe was transparent. Our universe is never, ever going to be truly transparent. 

Fraser Cain [00:11:40] We can. 

Pamela Gay [00:11:42] We can, we can totally look out. And we still see. We call it the Lyman Alpha forest, these clouds of neutral gas between us and distant systems. So these kind of have to pick a moment where it’s like empty enough. 

Fraser Cain [00:11:57] So we’ve got this time where I guess those first stars are starting to peep out of the dense fog, but they’re still large blobs of this fog, even to this day, are out there in the universe, but they’re becoming less and less dense over time. And so why is the cosmic dawn so difficult to observe? You would think that these incredibly bright stars out there would be obvious. 

Pamela Gay [00:12:28] So we have three problems. One is all the stuff that wasn’t transparent yet. So? So. There’s still clouds out there, so trying to find the stuff is difficult. Then there’s the whole. It’s giving off light from the beginning of the universe that has all been shifted into the infrared, where until very recently we didn’t have the capacity to really look directly. And even though we now have the capacity to look directly, there’s this problem known as they’re really, really tiny and faint. So even with austere, which can see the right colors, we need to use gravitational lensing to start to magnify the light from these objects. So first you have to have g t to see the correct color. Then you need a galaxy cluster to gravitationally lensed things. And then, of course, you have to figure out how to, like, make the gravitationally lensed thing make sense because it’s distorted. 

Fraser Cain [00:13:41] Yeah. I mean, even if you have a star that is 100,000 times more massive than the sun and it’s putting out a ludicrous amount of radiation. Yeah, it is nothing compared to a quasar, and we can just barely find quasars at 12 billion light years travel time. You know, like, yeah, just a couple of billion years after the Big Bang. Hubble would need gravitational lensing to see quasars that are less than a billion years old in most cases. Yeah, and so even a ludicrously bright star is not bright. Considering the distances involved. 

Pamela Gay [00:14:27] And this is where we’re lucky, because what we’re actually looking for isn’t so much individual stars. Although, I mean, if we could do that, that would be amazing. We would love to do that. 

Fraser Cain [00:14:40] Just please. 

Pamela Gay [00:14:41] Yes, more of that. But what we’re looking for is these new baby galaxies that have clusters of star formation costars luckily like to form in groups. And they also have, like I said, these active black holes in their center. So we’re we’re still working to piece together. And and this is something I love seeing how science changes. And we’re getting old enough that we have seen science change. It’s it’s we’re starting to realize it’s not just the stars. It’s also the supermassive black holes and their accretion disks that are blowing bubbles in the early universe that are helping make things transparent. 

Fraser Cain [00:15:29] Right. And so if you were to like, say, you were to like, look in your telescope and look and go, oh, I see cosmic Dawn. Look at that cosmic dawn. That is so much cosmic dawn going on over there. What would you be seeing? 

Pamela Gay [00:15:46] I would be seeing mostly if theory is right and and here we have to put a huge question mark. I would be mostly seeing small galaxies that look rather like dead lightning bugs on a windshield in the Texas summer, and they are rich in splatters of bright blue star formation. I would also see larger galaxies that structurally look somehow remarkably like galaxies we have today, like our own galaxy, like the Andromeda galaxy in structure. But again, they’re populated by massive young stars. And the reason I had to put so many caveats on this is J ust here’s updating our understanding of this so fast that part of me is worried by the time this episode is edited and goes live in seven days, some of what we say will already be outdated. 

Fraser Cain [00:16:47] Okay, so just as an example of this, like you remember, there was these did these discoveries of these galaxies that were impossibly large too early in the universe. So a week ago I, a simulation called Renaissance overturned that and said, actually, those galaxies fit perfectly well within various models of of the early universe formation. And you’re like, okay, yeah, that makes sense, right? Like we need a better models. And then this this week we got new evidence that, in fact, those galaxies might be even more massive than astronomers originally thought. And that’s like, that’s like a month, a month’s research into this goes galaxies found. They’re too massive. Oh, no. Actually, those fit the theories. Oh, no, those galaxies were more massive than we thought. Yeah, you’re exactly right. The research is coming so fast and furious. We. It feels like I research. We could barely keep up with it. Let’s talk about observing. Cause you don’t. Because you sort of went into this a bit that you need some kind of gravitational lens with s t to take a crack at that. So what what are the sort of the physics involved here? Or I guess the, the trigonometry involved? What’s going to be happening for you to be able to see some cosmic a little bit of cosmic dawn in your. 

Pamela Gay [00:18:12] Yeah. James t relativity meets trigonometry I think is definitely the right way to look at this. So we have g t with its giant mirror out there, and it will take an image of a massive, galaxy cluster. This is an object that has thousands and thousands of galaxies in it, a bunch of dark matter. And. If you have the the galaxy cluster and behind it you have light from a distant galaxy. Some about light is trying to shine straight towards us. Some of that light is trying to shine somewhere else in the universe, but it’s going to get bent towards us by that gravity. And because these galaxy clusters don’t have a smooth distribution, they’re not a perfect lens. They’re more like a carnival lens. All of these bent towards us, light images that weren’t meant to come our way are going to be completely distorted, stretched out, turned into basically streamers of galaxy. Like someone put the galaxy in Silly Putty and stretched it around the edge of a plate. But the thing is, it’s not going to be just like one planet’s worth of light that gets bent our direction. It is a vast quantity of light that we never would have gotten to see that that is acting like a massive telescope funneling light. So we have j ust being a light bucket. We have the galaxy cluster being a light funnel. And all in all, we’re able to start seeing things from 300, 600 million years after the Big Bang that appear in these images, as bright as the galaxies in that galaxy cluster. 

Fraser Cain [00:20:24] So what is cosmic like? If we could observe cosmic dawn with data to see, what does that tell us about the universe? 

Pamela Gay [00:20:32] Well, what’s interesting is we’re starting to hone in on it. Now, the problem that we’re having is we have to look at a galaxy cluster, identify the gravitational lens in the galaxy cluster, and then measure where that gravitationally lensed object is. We have found objects that clearly still have the clouds of material around them. We have also found objects that are free and clear that are only a couple hundred million years apart. So the light ionized the universe very quickly. And so what we know is the universe goes from that island of clearness in the fog that is surrounded by blue with different density, getting shocked by the bubbling out UV light surrounding it to everything is just transparent with random clouds. 

Fraser Cain [00:21:29] And I mean, I guess there are all these dynamics. You know, the age old question did the stars form first or did the supermassive black hole form first? Did they form together? Was it did these galaxies assemble together into larger structures? In what order? How do we get such massive galaxies so early on in the universe? 

Pamela Gay [00:21:55] And supernovae? 

Fraser Cain [00:21:56] What role did dark matter play in funneling and channeling the the structure of these galaxies? When? What could help account for the, the crisis in cosmology, like the difference in measurements between the early universe and that’s a different, you know, for sure. But the and we’ve done a different, you know, another round. 

Pamela Gay [00:22:19] Yeah. Yeah. 

Fraser Cain [00:22:20] But like just to see like was there some process going on that was already present that helped account for that change in measurements. So there’s I mean there’s just there’s so many questions get answered when you see the or you finally have a full picture. Like like we. Can’t see the first third or we have it until now, really seeing the first third of the universe’s evolution. 

Pamela Gay [00:22:45] Yeah. And what I’m loving is we go from this idea of you have something hot with UV light creating a bubble around it. Well, if you just wait one star at a time to make bubbles, you’re going to end up with a bunch of ionized things that look like a cluster of grapes, which is fine, but not entirely effective. And so they’re looking at things like supernova explosions are able to basically pop holes out of the disks of galaxies that allow light out. You have jets that are able to pop holes. And so you have all of these different things working together. And so it’s blowing bubbles and poking holes and blowing bubbles. And it’s so much more chaotic and dynamic than these simple pictures we wanted to be true. And the idea that it’s either primarily stars or black holes know both. The universe always says both and and I love that about the universe. 

Fraser Cain [00:24:03] So the universe is a game of Wordle? 

Pamela Gay [00:24:07] Yes. 

Fraser Cain [00:24:08] And we have this. We have the first character cosmic. We background radiation. We understand that. But the kind of starting point. Yeah. And then we have the last like four letters. 

Pamela Gay [00:24:22] Yes. 

Fraser Cain [00:24:24] From like quasars through till the modern universe. We’re missing two those first two. 

Pamela Gay [00:24:32] And we’ve tried all the vowels. So. Right, right. We’re stuck knowing it’s a consonant and. 

Fraser Cain [00:24:39] T is helping us work out character number three. Yeah. And we probably and we’ll give hint some character number two, the cosmic dawn. There was, you know, there was this other set of giant observatories that were planned. Of course, everyone’s familiar with luvoir and hatchbacks, but there was a an x ray telescope called Lynx, and then there was origins. And origins was going to be a beefed up version of T that would be in the 12 meter range. Yeah. And would it be capable of directly and would have farther infrared, more like Spitzer beefed up to mega T size. And it would be the machine that would directly observe those first stars forming a cosmic dawn. And it’s been shelved. 

Pamela Gay [00:25:27] Yeah, everything keeps getting shelved. 

Fraser Cain [00:25:30] Yeah, yeah. 

Pamela Gay [00:25:31] That’s another show that’s much more depressing that we’re not doing this year. Maybe next year. 

Fraser Cain [00:25:35] Yeah. So, half. Can we do that? Can we do an episode about the missions? That being that this missions that have been canceled that make us sad? I feel like that that does meet your criteria because they didn’t fly. And so now we can talk about how they make it sad. Yeah, I think it’s reality. We should totally do that. All right. Thank you. Panel. 

Pamela Gay [00:25:59] Thank you, Fraser, and thank you to everyone out there who is part of our Patreon community. You allow this show to to happen this week. I would like to thank Aaron Zegras, Michael Regan, Omar Del Rivera, Scott Briggs, Dan Mendes, Benjamin Mueller, Janelle, Jay, Alex Alexander, J, Alex Anderson, Peter Frodo, tannin, Bo Jim McGinn, Kenneth Ryan, Matt Rucker, Dean McDaniel, Mark Steven Rusnak, and Michelle Cullen share some Mark H. Whittock, Philip, Grand father Abraham Cottrell, Bruce. Amazon, Dwight. Elk, James, Roger and and Esau. Thank you all so much. 

Fraser Cain [00:26:52] Thanks, everyone. We’ll see you next week. 
Pamela Gay [00:26:54] Bye. 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 Doctor Pamela Gay. You can get more information on today’s show topic on our website. Astronomy. Cars.com. This episode was brought to you. Thanks to our generous patrons on Patreon. If you want to help keep the show going, please consider joining our community at Patreon.com Slash Astronomy Cast. 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 Astronomy Cast.