Mysterious objects near the beginning of time

Astronomers are putting together a new picture of the early universe. It involves a lot of very weird black holes, and it could help us understand how our own galaxy formed. Guest: Caitlin Casey, astronomer at UC Santa Barbara ⁠ For show transcripts, go to ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠vox.com/unxtranscripts⁠⁠ ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠For more, go to ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠vox.com/unexplainable⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠ And please email us! ⁠⁠⁠⁠⁠⁠[email protected]⁠⁠⁠⁠⁠⁠ We read every email. Support Unexplainable (and get ad-free episodes) by becoming a Vox Member today: ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠vox.com/members⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠ Thank you! Learn more about your ad choices. Visit podcastchoices.com/adchoices

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:01Speaker 00

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• 0:49Speaker 01

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• 1:27Speaker 02

  It's Unexplainable. I'm Sally Helm. And today, I'm delighted to remind you about the existence of outer space.

• 1:38Speaker 02

  While I am doing things like compiling my documents for tax season or deciding whether it is time to replace the kitchen sponge, I sometimes like to pause and remember that astronomers are out there probing the many mysteries of the universe. I mean, astronomers do have to deal with their own kitchen sponges, but they also get to do things like look at the images sent back to Earth by this enormous, amazing telescope, the James Webb Space Telescope.

• 2:12Speaker 02

  JWST for short. It launched on Christmas Day 2021. We've covered it on the show before. But JWST is so powerful that it can essentially peer back in time. It allows scientists to see things that they have never seen.

• 2:31Speaker 03

  I use every second that I can squirrel away from my family, from teaching my classes at the university. I use every second of every day to just look at these images and dig deeper.

• 2:44Speaker 02

  We heard from astronomer Caitlin Casey about two years ago. I recently called Caitlin to check in, and she was right back where we left her, looking at the images that this ginormous telescope is sending back to us on Earth. Is the novelty, like, starting to wear off?

• 3:04Speaker 03

  Absolutely not. The novelty is there every single day. I'm still just as excited to look at JWST data as I was in July of 2022, when we all got to see images for the first time. It's given us so much of a new picture, a new lens on how the universe came to be. I just can't get enough of it.

• 3:30Speaker 02

  The last time we talked to Caitlin, she told us about a mystery in the very early universe. These little smudges of light appeared all over JWST images. They were red, and they were weird. One theory at the time was that they might be massive galaxies. But if they were, they were too big too soon. Here's what Caitlin told us back then.

• 3:57Speaker 03

  Some folks want to throw out our cosmological model completely. And that is, you know, that would change everything we think we understand about the universe.

• 4:10Speaker 02

  The other theory was that they might be supermassive black holes. But that also had people freaked out.

• 4:18Speaker 03

  The reason that is disturbing is because, just like we don't know how to form stars really quickly, we have really no clue how to form black holes that are so massive. In the assembly of all of this research, I think we'll start to emerge with a new picture of the infant universe, this first couple hundred million years. And hopefully, you know, the next year or two. I'm not gonna, don't quote me on that.

• 4:50Speaker 02

  Well, it's been two years now. Time to quote her. Sorry, Caitlin. But she did have some major updates. For one thing, those mysterious smudges of light have gained a new name. Little red dots. And it seems like they're called that because they look like little red dots? Is that right?

• 5:08Speaker 03

  That's right. Shocker, shocker. Yes, little red dots are probably the most popular topic at scientific conferences discussing JWST data right now. I think we're converging a little bit. We're in a bit of a better place than we were two years ago, the last time I talked to y'all. But it's, you know, a big mystery and so many details to unravel.

• 5:33Speaker 02

  Yeah, it does sound to me like you guys are starting to hone in. And it sounds like it's door number two. We're going in a black hole direction?

• 5:42Speaker 03

  For little red dots, yes, it's door number two. We're talking about supermassive black holes. I would say, I mean, you know, not everyone is sold on that yet. Now, that actually doesn't close the door entirely on door number one. There's still some really puzzling mysteries where we have really massive galaxies formed too early. But the overabundance of these little red dots in particular, that is pointing more and more towards the supermassive black hole hypothesis, that there are just oodles and oodles of black holes in the early universe, and we don't know what to do with them.

• 6:20Speaker 02

  Supermassive black holes are this giant mystery. We do not know why there seem to be so many of them hanging around in the early universe. But there is also a supermassive black hole at the center of our own galaxy, and we have no idea how it got there.

• 6:54Speaker 02

  If you looked at a picture of a little red dot, you would see a little red dot. But JWST is not like you and me. If you point it at a little red dot, it can show you the invisible light, light that can't be perceived by the human eye.

• 7:11Speaker 03

  We disperse the light into effectively a prism. And that's like giving us a chemical fingerprint of what's inside that object. And there's a specific signature that black holes have that you can't really get any other way. You have to have a really massive object with material around it that's whipping around really, really fast. And it's whipping around really fast because it has such a strong pull of gravity. We have seen this over and over again in the spectra of little red dots. So overall, the consensus is this picture of supermassive black holes.

• 7:55Speaker 02

  But there is something very weird about these black holes.

• 8:00Speaker 03

  Let me first, you know, set the scene of what a typical supermassive black hole looks like.

• 8:06Speaker 02

  Astronomers are used to seeing supermassive black holes embedded in galaxies, in these big groups of stars.

• 8:16Speaker 03

  Every galaxy has a supermassive black hole at its center, which should sound shocking and also pretty profound. So the Milky Way is huge. It has a diameter of something like 100,000 light years. To put that into, you know, proportion relative to the black hole, I'm going to use an analogy. So if the Milky Way disk is about the size of the continental United States...

• 8:45Speaker 03

  The supermassive black hole at the center of the Milky Way would be about the size of the tip of a pencil.

• 8:55Speaker 02

  Wait, sorry.

• 8:56Speaker 03

  Galaxies are enormous. Black holes are tiny. The tip of a pencil inside of the continental United States.

• 9:05Speaker 02

  Not even the eraser, the tip of a pencil.

• 9:08Speaker 03

  Not even the eraser. Yeah.

• 9:12Speaker 03

  Now, the black hole, because it's actually so massive, it typically weighs about 1 one-thousandth of the total mass in a galaxy. That's a lot for just the tip of a pencil compared to the continental United States.

• 9:27Speaker 02

  But that relationship, 1 one-thousandth, it's pretty consistent across all galaxies. The assumption has basically been that the black hole and the galaxy grow together, that they've kind of like always been linked. But little red dots might be telling us a different story.

• 9:50Speaker 03

  Little red dots are so puzzling because they seem to be isolated black holes. We don't know why the galaxy that should be surrounding them seems to be missing.

• 10:06Speaker 02

  Hmm. A missing galaxy. Where is it? One possibility is that the galaxy is there, but hiding.

• 10:18Speaker 03

  What we call a galaxy in the first billion years of cosmic time is very different than what we, you know, see in these gorgeous pictures from Hubble and even JWST of nearby galaxies that, you know, they have spiral arms and really sophisticated structure. Galaxies in the early universe are much, much smaller than galaxies are today. They lack organized structure.

• 10:43Speaker 03

  It's possible that the galaxy is there. It's maybe just a collection of a few thousands or tens of thousands of stars. Those stars might look very different than stars in the universe today. They might be exotic types of stars. But I think we're coming to the consensus that wherever they are, they're much fainter than the material that's being collected around the supermassive black hole that is shining brightly as the little red dot.

• 11:23Speaker 02

  It's also possible that the galaxy is not there and that we're learning something entirely new about how galaxies and supermassive black holes form.

• 11:34Speaker 03

  Maybe the discovery of little red dots is telling us that the black hole forms first, I guess, and the galaxy lags behind. It's a bit as if if a human were, you know, developing as an embryo, right? And only the heart grows first. And then the heart is born alone. And then the rest of the human grows around the heart. It would be like two things are wildly out of sync.

• 12:05Speaker 02

  Yeah, it's like a bunch of hearts floating around in space without their bodies.

• 12:10Speaker 03

  Without their bodies. And it just doesn't make a whole lot of sense, given the consensus view of how these things grow through time that we've been, you know, building up for decades. And this is something that you can only really figure out by pressing up to the most distant objects found shortly after the Big Bang. You wouldn't, you wouldn't figure this out any other way because you need to see, you know, what came first. Is it the chicken or the egg? And, you know, here we're maybe seeing that play out in real time.

• 12:49Speaker 02

  But if the supermassive black hole forms first, that leads to an obvious question. Do we know how supermassive black holes come to be?

• 12:58Speaker 03

  Thank you for pointing out the elephant in the room.

• 13:03Speaker 03

  Yeah, it turns out that while supermassive black holes are everywhere in the nearby universe, we just don't know how they formed in the first place. We now are thinking that Laura dots are an essential piece of the puzzle.

• 13:21Speaker 03

  That's after the break.

• 13:26Noam Hassenfeld?

  Support for the show comes from Sonos. Hey, Sonos, give me some music.

• 13:32Noam Hassenfeld?

  All right, one of life's great mysteries. You're listening to music in the living room, but you gotta grab something from the kitchen. You don't want to take the speaker with you, but you also don't want to miss that beat drop. And this is where I introduce you to the magic of Sonos. Sonos sent me a couple of speakers to try out, so I've got to move two here in the living room. And then I walk down the hall.

• 13:57Noam Hassenfeld?

  I get in here to the kitchen, and I got a brand new Sonos Play right here on the counter. I can open the fridge, grab a seltzer.

• 14:15Noam Hassenfeld?

  And yeah, I didn't miss a second. And I can make each speaker louder or softer in the Sonos app, or if I'm using AirPlay, so I can make it louder in the kitchen without blasting whoever is still in the living room. It's all just easy, and it sounds amazing. These speakers are crisp, they've got great bass, and I'm especially impressed with the new Sonos Play. It packs this truly awesome sound in a much smaller size. So I don't know, if I want to head outside for a minute.

• 14:51Noam Hassenfeld?

  It's super easy, and yeah, pretty nice out. Visit sonos.com and build your system. Sonos, love the sound, feel the system.

• 15:06Speaker 00

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• 16:31Speaker 05

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• 17:03Speaker 02

  It's big for me. Have you ever heard?

• 17:09Speaker 02

  Black holes. They are dark, they are massive. And there is one at the center of the galaxy that we are all in right now. My classic image of a black hole is of a dead star. This very bright thing that collapsed in on itself.

• 17:27Speaker 03

  So what you just described, astronomers call stellar mass black holes. These are objects that formed from the remnants of massive stars. They tend to have a certain mass range.

• 17:40Speaker 02

  They're like a couple of times the mass of our sun, or maybe even a couple hundreds of times.

• 17:46Speaker 03

  Supermassive black holes live in a different regime. They are about a million times the mass of the sun.

• 17:53Speaker 02

  And we've known about supermassive black holes in the early universe for a long time. Like, aside from these little red dots. We just have no idea how they got that big that soon.

• 18:06Speaker 03

  There is something like a speed limit to the growth of black holes. This is called Eddington limited accretion, for the fans out there.

• 18:18Speaker 02

  Eddington fans, we got you.

• 18:19Speaker 03

  Yeah, yeah, Arthur Eddington, he was pretty smart. So what Eddington limited accretion says is that there is a fundamental limit at which a black hole can gobble up material. The more it gobbles up, that's called accretion, it shines more.

• 18:41Speaker 02

  As the black hole gobbles up material, that material creates something called the accretion disk. This like swirling hot ring of stuff around the black hole. That is what shines.

• 18:56Speaker 03

  And that shining actually exerts a pressure on the disk itself. So it's as if the gravity of the black hole pulls everything in, but the shining of the disk pushes everything out. And if you crank up the speed at which the black hole accretes material, it's going to shine too brightly that it'll actually cause the disk to effectively blow up.

• 19:31Speaker 03

  And it won't be there anymore.

• 19:35Speaker 02

  It is not clear how these supermassive black holes got so big so early without breaking that speed limit. There is a theory called super Eddington accretion, basically a way that, under certain conditions, black holes could grow faster. So then, maybe these are just dead stars that grew really fast. But it's really hard to actually observe that happening. And then there's been another idea floating around that maybe these supermassive black holes didn't start out as stars. Maybe they just started out as big gas clouds, and somehow those collapsed.

• 20:16Speaker 03

  Direct collapse black holes are a phenomena where you take a primordial gas cloud. That sounds pretty fancy, but it's literally just a giant ball of hydrogen gas that comes fresh from, you know, the formation of the Big Bang. If you have this primordial gas cloud, some theories suggest that you can instantly collapse into something much more massive than any star that we see in the nearby universe. It's, you know, one of the many possibilities that as you have more primordial gas clouds, you can form more exotic objects that we just don't see in the universe today.

• 21:00Speaker 02

  JWST has let us see an earlier freeze frame of the universe than we have ever seen before. And one extremely obvious part of it is these little red dots. So maybe they somehow fit into this story. That is one reason that scientists have been so obsessed with pinning down precisely what they are.

• 21:26Speaker 03

  Little red dots are a puzzle, A, because they're red.

• 21:33Speaker 02

  Now, a lot of things in space that are very far away look red to us because of the way the light travels. But little red dots actually are red.

• 21:44Speaker 03

  These are intrinsically red. Like, if a little red dot was right next to you, it would look red.

• 21:50Speaker 02

  Now, black holes themselves are not shining. It's the accretion disk that's giving off light. And the brightest supermassive black holes that we have seen in the past, they have been blue. We call these quasars. So if little red dots are supermassive black holes, it's just weird that they're red.

• 22:13Speaker 03

  The typical explanation for red things in the universe is that there's dust. Things are reddened by dust. It's similar to a hazy sunset. And so, team after team has searched for dust in little red dots, and we just aren't finding it. So little red dots don't seem to be red because of dust. They seem to be red because they're fundamentally different black holes than the typical quasar we've known and loved for decades. And that gets us to the interesting idea

• 22:55Speaker 03

  of these being surrounded by, not dust, but effectively, an atmosphere of a star.

• 23:06Speaker 02

  This primordial star gas could be what is making the little red dots red. And this combination, a supermassive black hole wrapped in the atmosphere of a star? We have never seen this before. We didn't know that it happened, let alone that it happened so often in the early universe. It's kind of a new object in space. Some people have now started to call the little red dots "black hole stars."

• 23:42Speaker 03

  So little red dots, we knew nothing about them before JWST. They're only in the early universe. So we're just pushing now JWST to do a better job to find little red dots even earlier in the first 400 million years of cosmic time because there are a lot of different ways that little red dots can teach us about supermassive black holes, how black holes grow at the beginning of time, and how supermassive black holes relate to the galaxies that they live in and we see in the universe today.

• 24:22Speaker 02

  Maybe all supermassive black holes were once little red dots, or maybe not. There's a lot that we still don't know.

• 24:29Speaker 03

  One detail I'll add is that, you know, we have guesses as to how massive the supermassive black holes and little red dots are. But, you know, those guesses are calibrated off of black holes we know and understand in the nearby universe. And maybe some of the fundamental relations that we take for granted in the nearby universe just don't hold at early times. So we actually might not know the masses as well as we think we know them. And it turns out, you know, guessing the mass is pretty important to understanding how the thing formed. We do the best job we can just looking up at the night sky.

• 25:11Speaker 03

  But we don't have real experiments that we can conduct on the universe itself.

• 25:18Speaker 03

  You know, what I love about this field is it always has a surprise for you. You know, we turned on JWST a couple of years ago, and it felt like we went from a black and white world to a colored world. And with every leap, you learn something completely surprising about the universe. And here, I think it happens to be this story of the first billion years of cosmic time. It's complex, it's messy, there are a lot of black holes. We have no idea how they form. And we don't know where the galaxy is around them.

• 26:03Speaker 03

  And it should be there. I don't have answers today for you. But, you know, we're, we're working on it every, every single day. Maybe, maybe in another two years, we'll have answers.

• 26:19Speaker 02

  If you do come back on Unexplainable for appearance number 015 in 10 years down the line, what would you hope to be able to tell me?

• 26:28Speaker 03

  That's a great question. And, you know, the true answer is that I would never be able to predict it. The most exciting thing are the things that I can't even imagine.

• 26:46Speaker 02

  This episode was produced by me, Sally Helm. It was edited by Meredith Hoddinott and Joanna Solotaroff. Christian Ialla did the sound design and the mixing on this episode. Melissa Hirsch checked the facts. Jorge Just and Julia Longoria are our editorial directors. Amy Padula and Noam Hassenfeld are some of the things that the James Webb Space Telescope has not yet been able to see. And Burt Pinkerton waited for a response, but no one could help. So she went to the octopus. Where's Eric Flaptin? The octopus shook her head. In a white room with black curtains. In the station where the sun never shines. Where the shadows run from themselves.

• 27:34Speaker 02

  Thanks, as always, to Brian Resnick for co-creating the show along with Burt and Noam. And special thanks today to Anna D'Arif for helping me understand little red dots. If you have thoughts about this episode, or about the show, or about outer space, please write to us. We are at [email protected]. Getting these emails is really a highlight of our day. So if you are on the fence about writing in, I say go for it. If you want to support the show and help us keep making it, please join our membership program. It is at vox.com/members. You get ad-free podcasts and unlimited access to Vox Journalism. You can also help us out by leaving a nice rating or a review,

• 28:19Speaker 02

  or just by telling people in your life to listen to Unexplainable. We really appreciate all of that so much. Unexplainable is part of the Vox Media Podcast Network, and we will be back in your feed very soon.

• 28:46Speaker 06

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