Daniel and Kelly’s Extraordinary Universe - Could stars have black holes at their cores?

Episode Date: July 22, 2025

Daniel and Kelly dive deep into the event horizon and discuss an outlandish theory of stars with black hole cores.See omnystudio.com/listener for privacy information.

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I'm Dr. Joy Hardin Bradford, host of the Therapy for Black Girls podcast. I know how overwhelming it can feel if flying makes you anxious. In session 418 of the Therapy for Black Girls podcast, Dr. Angela Nielbornette and I, us flight anxiety. What is not a norm is to allow it to prevent you from doing the things that you want to do, the things that you were meant to do. Listen to therapy for black girls on the iHeart radio app, Apple Podcasts, or wherever you get your podcast. black holes. We always seem drawn to cracking things open and looking for the surprises inside. We've been walking around on this planet for hundreds of thousands of years and

until recently had no idea of what was hidden within. Was it all just dirt? Is it hollow? Was Godzilla sleeping in his lair down there? What about in the hearts of stars? Science tells us that at their core, matter is incredibly dense. The fusion furnaces that illuminate the universe and forge the heavy metals needed for life and podcasts. But what if there was something else even more exotic in the hearts of stars? What if, instead of iron or nickel or even nuclear pasta, stars' hearts might contain the most mysterious objects in the universe, black holes? And what if that could solve another long-standing cosmic mystery? Today on the pod, we'll ask whether stars could have black holes at their cores. Welcome to Daniel and Kelly's extraordinarily

dense but brilliant universe. Hello, I'm Kelly Weider-Smith. I study parasites and space, and I love pizza. My name is Daniel. I'm a particle-featry. physicist, and I'm particularly particular about my pizza. I remember you and I had a discussion once about what we were like level 20 experts on, and you said that you were like a level 20 expert on pizza, and I'm embarrassed to say I couldn't figure out anything to say that I was a level 20 expert on. But anyway, you just visited Chicago, and so I have to ask you a very important question, which U.S. city makes the best pizza?

It's easy. New York, obviously. New York pizza, hands down. I'm so glad we can stay friends. I wasn't sure if this was going to be like a white chocolate, dark chocolate divide, where I admit that I actually don't dislike white chocolate that much and then you get upset and then I pretend that I hate it moving forward. But, yeah, New York does have the best pizza.

It's similar to that, actually, because some people defend Chicago pizza. And it's a tasty thing, but it's not pizza. Yeah. You know, it's like a marinera bathtub or something. I mean, it's delicious and greasy and it's good, but it's not pizza. And when I got to choose and I got to make it myself, I'm definitely making thin crust pizza, though with a little bit more of a neapolitan puffy crust around the edge. Yeah, I love that all. I mean, I love all kinds of pizza, but yeah, whenever I go to New York, I've got to get some pizza.

And I don't know why they got to call it pizza, you know, like they don't call the Chicago hot dog like a taco, you know, like just call it its own thing. Why reuse this word pizza for something, which is totally different from pizza? I mean, it's got the same ingredients, but just in different, like, depth. No? You disagree? I don't know. I recently tried Detroit pizza. Also quite tasty, very weird, delicious, but still, in my opinion, not pizza. But, you know, that's semantic. It's all delicious combination of excellent ingredients. My personal preference is the thin stuff. But, you know, I get why people like Chicago pizza. We won't talk about pizza for that much longer because we have important science to get to. But I heard that Detroit pizza is like in an automotive pan of some sort or like what is the defining feature of Detroit pizza? Presumably you clean the pan first.

Detroit is also a deep dish kind of pizza, but you have like sauce on the top in these rows on top of the cheese. And you get this crispy edge that cooks up if you do it right. Anyway, it's quite good. Okay, I should have eaten before we started recording this because now I'm hungry. But all right. But, you know, if you eat too much Chicago pizza or too much Detroit pizza, you risk collapsing into a black hole. Oh, that's where I was going. You got there first. Oh, I was actually going to, like, contribute a transition. But, okay, so today we're talking about black holes. All right. And we are specifically talking about whether or not stars could have black holes at their core. And I will be honest, when you first sent this question to me, my thought was, well, could a star exist if it had a black hole at its core? It seems like the answer should be no.

And so let's see if our audience's guts had the same response. No matter what pizza they happen to be digesting. We hope it's delicious, no matter what it is. I guess stuff in the core of a star could get dense enough that it would turn into a black hole. But maybe that will eventually end up extinguishing the star because I can see how the star could keep on burning only with its outer shell. So I guess if that happens, it will be short-lived and the star will die. turn into a black hole. I suspect a star can have a black hole for a core

as long as the star is both big enough to survive the initial black hole formation and big enough that the black hole's gravity doesn't affect the outermost layers of the star. I suspect not. It would collapse the whole star material, I think, into itself, plus no longer being a star. I think there is possible to have a black hole

inside a star in the core because a black hole can be small enough, even for you to have it in your hand, isn't it? And it would not affect the surrounding because it's more. I don't believe a star could have a black hole core, mainly because for one to form in the first place, a star would have to collapse. And if there was such a condition where it did have a black hole as its core,

the gravitational force would pull in the surrounding matter that makes up the star anyway, so it could never be stable enough. It seems possible, but then you'd have to ask, how did it get there, and how does it stay there? And I don't know how it would form, but for it to stay there, the star around it would have to be spinning very, very fast so it doesn't get pulled in. And I don't really know how that would ever start happening. Okay, so I'm feeling pretty good because a handful of our audience members had the same feeling as I did. And, you know, I haven't gotten to the end of the outline yet, so I don't know if I'm right or if I'm wrong.

It'll be an exciting journey that we'll take together. And these are great ideas. I like the way they're thinking. But, you know, it strikes me that a lot of people think of black holes is like this infinitely powerful thing that will suck in anything. But, you know, we've seen pictures of black holes, and we know what black holes should look like out there in nature. And they're not totally by themselves. You can have stuff around the black hole. Like the famous picture of a black hole has a hot disk of gas right around it because the environment around a black hole is quite complex.

And there's pressure out and gravitational attraction in. And so we're going to learn it's not quite so simple. Yeah, I was talking to Sarah Gallagher at Western University the other day, and she studies the gases that, like, emit out of black holes. And I just kind of stared at her for a second because I was like, I didn't think anything could escape from black holes. And so we had a fascinating conversation about how I was wrong. Yeah, well, you're right that nothing can escape from a black hole, but things can escape from the vicinity of a black hole. So it depends what you count as the black hole. If it's a black hole, plus it's accretion disc and all that stuff, then yeah, it can emit, and they certainly do.

We see quasars from across the universe, these incredibly bright emitters. Okay, but I think we can all agree that nothing escapes from the center of a black hole. So if you are a star that has a black hole in your belly, it feels like that shouldn't work out. So where do we start? What do we think stars have at their center? Yeah, stars already super fascinating objects, even without the black hole, right? It's incredible that these things exist. They're this delicate balance between gravity and fusion.

but they're also stable. They can last for millions or billions or we think sometimes trillions of years. It's really incredible. And understanding what's going on at their heart has taught us a lot about the nature of physics and even chemistry. Yeah, I also had the urge to sort of spit and cough.

So I understand. I'm going to wipe my face before we go on. And also the distribution of stars that are out there, the sizes, the colors, the ages. Tell us a lot about the history of the universe. I love this about science that you can piece together a whole history from what you see around you. It's not just like, does this work, but it's like, how did we end up here?

Why do we have this arrangement of stuff? And not some other arrangement. There's so much information just encoded in what's out there. So I love that we can dig into it. And from that, we've put together a pretty good model for how stars form and what should be at their center before we get into exotic black hole stars. Yeah, I also love that kind of detective work into the past using science to understand and things we couldn't have seen.

But, okay, let's jump into stars. What should be in the center of those stars? So stars are basically just a scoop of universe. You know, go all the way back to Big Bang, hot, dense soup of stuff. It expands, and therefore it cools, and you get particles that form. You get electrons and quarks,

and then the quarks bind into protons. And then you have protons and electrons in the universe. It keeps cooling, and those electrons then get captured by the protons, and so now you have hydrogen. And most of the universe at the very beginning is hydrogen. It's like overwhelmingly hydrogen, tiny little bit of helium that forms because you can actually have hydrogen fusion during the first few moments of the universe to make a little bit of helium trace anything else.

So the universe is hydrogen, but it's not perfectly smooth. The original quantum fluctuations in the early universe lead to over densities in some places and under densities in others, which gives gravity a handle to pull that stuff. together to make stars. And so you have these big clouds of hydrogen. Some spots are a little heavier. They have more gravity. They pull on more hydrogen, gives them more gravity, gives them more hydrogen. You get this runaway effect and then you get a collapse. So the first stars, we think, were mostly hydrogen and a little bit of helium. And if you were explaining how black holes are formed, would you have used all the same words? Or is that a totally different process?

no basically the same but you need to get to a critical density to form a black hole and what happens when a star is collapsing is that gravity isn't the only game in town you get to a certain density at the core of the star and it ignites fusion so it's hot enough and it's dense enough that the protons which don't usually like to talk to each other because they're both positively charged are squeezed together close enough that eventually they will fuse and they'll give you helium and release some energy So this is fusion. You get protons fusing into helium and energy comes out. And that energy pushes back out on the star.

It's effectively a pressure outwards. So you have gravity squeezing in and fusion and radiation pressure pushing out. That's what keeps the star from collapsing into a black hole. So you're right. Black hole collapse is very, very similar. But you don't get there in a star because of fusion. Fusion keeps the universe from collapsing into black holes and keeps it bright, right? Without fusion, we wouldn't have light in the whole universe.

would be dark. Thank you, Fusion. If only we could use it to power our toasters. We'll get there one day. And this is not the primary topic of today's episode, but there is a theory

that in the very, very early universe, there might have been enough over density, maybe even before you formed all those protons to create primordial black holes, which exist like before there are corks and protons

and all sorts of stuff. So it's possible to form black holes in the very, very early universe. A lot of people ask, like, if the universe was super dense, why didn't the whole thing collapse into a black hole? And the reason is that for a black hole a form, you need density in one place relative to the density around it. If everything is super

dense, then nothing is getting pulled. But if you happen to have one spot, which is super over dense, potentially you could have direct collapse into a black hole in the early universe. But we're not talking about that today. We're imagining what happens to normal stars. So you get this collapse, you get fusion, and then you have a balance. Gravity and radiation are doing this delic balance. And it can keep going for millions and millions of years. And at the core, you're manufacturing new elements. So we're talking about what's at the core of stars? Well, it starts out with just hydrogen, and then you get helium. And if the star is big enough and massive enough, it could also fuse that helium into heavier stuff. You get carbon, you get neon, you get

oxygen. And if it's big enough and massive enough, you can get silicon, you can get all the way up to nickel and then to iron. So that's how we manufacture these elements. They're made at the hearts of stars. All right, let's see if I can pass the qualifying exam for my POD. If I remember correctly, the bigger the elements that you're getting, the more like heat you're losing and over time that cools the star, is that right? Almost. No, no, almost. You're definitely got the spirit of it is right. You know, up to a certain point, you are generating heat. So before iron, fusion creates heat. Like when you go from lighter elements to heavier elements, you release heat. Above iron, fusion costs heat, right?

It takes energy. So it can happen because there is energy there, but effectively cools the star when you fuse iron nuclei together to make something even heavier. And so that doesn't mean it doesn't happen, but it means it effectively kills the star. Because now the star is cooling down, and if it's cooling down, it can't push back against gravity.

And what do you have is you start to have a gravitational collapse again. And then you can form like a normal vanilla black hole, like the kind that we have seen in our universe. where the whole star becomes a black hole. And we're talking about that a little bit more detail in a minute. But there's another thing that we need to understand first about normal stars, which is the limit on their size and the connection between the size and the age of the star. You have the whole early universe, big clouds of hydrogen,

some clumps of which collapsed to make stars. And you might wonder, like, is there a limit to the size of the star? Like, can you just get huge clouds that form together to make enormous mega stars? And the answer is that there is kind of a limit. because the bigger the star, the higher the pressure and the density and the temperature of the core, and the faster fusion happens, because fusion is very sensitive to the temperature and the pressure. Like you increase the pressure by a little bit, the rate of fusion increases very, very quickly. And so what happens if you have a star that's too big is that the radiation pressure from the fusion is so intense

that actually blows the star apart. It'll like rip apart the star and blow away its outer layers. Wow. So effectively, you can't get a star that's... like more than 300 times the mass of our sun, it'll tear itself apart. That would be a pretty epic way to go. I think my new goal is to become super massive towards the end of my life. Blow yourself apart from the fusion at your core. That's what happens if you eat too much Chicago pizza.

Yeah, you got to be careful. You got to be careful. And there's something else happening at the core of the star, which is really crucial. You've made those elements, right? You've made helium or iron or nickel or whatever. They're at the core of the star, but when the star dies, it goes supernova, and it blows that material out into the universe. And then those heavy metals become the seeds of the next generation of stars. So when we start out, we have a universe mostly filled with gas that makes these really big stars, huge stars that don't last very long, maybe a few million years because they're so big.

But the next generation, it's different because now you have these heavy seeds to start stars. You don't just have to have a big hydrogen clump to start a big hydrogen star. you have like a blob of iron over here and some nickel over there and those are excellent at seeding new stars. So then the next generation of stars are smaller because there's like more places to start so the big clouds of hydrogen break up into more chunks

and because they're smaller, they don't burn as hot and they last longer. So the second generation of stars that have more metals in them last a lot longer than the first generation and are also smaller. That is beautiful, but my brain has gotten totally off on a tangent imagining Kelly at the end of her life

exploding into lots of little Kellys and that really would be a great way to go. Next generation of Kellys will all be mini-kellies, yeah, exactly. That's right, that's right. But at least there'll be more of them. Anyway, that is beautiful that a giant star produces more stars.

Yeah, exactly. And in our universe, we still have some big stars. Like, if you look at the star mass distribution, mostly the stars in the universe are smaller. Like, our star is on the heavier, larger side compared to the average star. We have a yellow star, but most of the stars out there are red dwarfs. They're smaller and colder, and therefore they burn cooler than our star.

So the smaller the star, the cooler it is, the bigger the star, the hotter and bluer it is. So if you look out into the universe, you can actually tell the age distribution of stars because the blue stars disappear more quickly. So if you're like looking at a part of the universe and there's a bunch of blue stars, you know that stars have been formed there recently. Whereas if you look at some corner of the universe, you're like, oh, it's all red stars, then you know there have been no stars born recently. It's like a retirement home versus a new subdivision or something.

But, like, could you make a reasonable guess at star siblings? Like, this star exploded and produced these 30 stars in response. You can understand star siblings in the sense of, like, you can estimate the age of a star from its neighbors, right? Like, if there are no blue stars around, you can guess that it's probably older. And if there's lots of blue stars around, you can guess that it's probably younger. which really hard to trace back an individual star and say if this one was formed from the explosion of that earlier star

which no longer exists and the other ones that came from that star, that's really tricky. And also it's complicated because our son was formed from the remnants of other stars, but not just one, right? It's not like one chunk

of some other star landed in a gas of hydrogen. It's like a huge conglomeration of probably many, many stars that all came together. So yeah, the family tree gets pretty messy there. Yeah. It's like a big orgy

that happened to make our star. Oh, good, good. Way to make this a non-kid-appropriate episode. You can have totally family-friendly orgies. You can have like an orgy of pizza, for example, right? Sampling lots of different pizzas. Yeah. I'm not sure that you know what people usually mean when they use that word, Daniel.

I know what people usually mean. I'm saying for folks that they're listening with your kids, there's an explanation for you. Yeah, I hope they don't repeat it at school. All right. So should we talk about any other stars on our tour of life? local stars? Yeah, so there are some really big stars in our universe, and they're really fun to think about because the sizes are just really incredible. A famous big star is Beetlejuice. Beetlejuice is... Oh, that's two. Don't say it a third time. That star is famous because it's in

Orion, and it has a radius a thousand times that of our sun. Wow. The sun is already enormous compared to Jupiter, which is gigantic compared to the Earth. And now, Beetlejuice, it's showtime, is a thousand times the radius, which means a billion times the volume. Holy cow. It's just hard to really wrap your mind around. If you put it in our solar system, its edge would be at the orbit of Jupiter, right? We would be inside Beetlejuice.

Also, it's a weird start because recently it's been seen to be dimming, so it's, like, quite variable in ways people don't understand, which some people think might mean. It's about to go supernova and there's interesting stuff happening at its core. But again, we don't really understand the core of star is in detail. It's so chaotic and difficult to describe with simple equations and expensive to model with supercomputers. So it's really an active area of research. But that's a really cool, really big star. So my interest in a topic is directly proportional to how much it impacts me.

So if Beetlejuice explodes, is that going to be bad for me? If Beetlejuice explodes, it'll be dramatic and exciting, but probably not super dangerous. It's 650 light years away. It's not the time of travel that keeps us safe. It's not like, oh, it explodes when we have 650 years to do something about it. We won't know it explodes until 650 years after it explodes because that's when the signal is going to arrive here on Earth. But because it's so far away, the radiation it produces will be quite diluted. That radiation is going to spread out in a huge sphere and cover the inside of that sphere.

And the Earth is a tiny, tiny slice of that. So we're only in danger to supernovas that are much closer than that. Okay, that's good. I feel great. Now that I feel great, let's take a break, have some pizza. And when we come back, we'll talk some more about some big stars in our galaxy. I'm Emily Tish Sussman, and on she pivots, I dive into the inspiring pivots of women who have taken big, leaps in their lives and careers. I'm Gretchen Whitmer, Jody Sweeten, Monica Patton, Elaine Welteroff. I'm Jessica Voss. And that's when I was like, I got to go. I don't know how, but that kicked off the pivot of how to make the transition. Learn how to get comfortable pivoting

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Listen to this episode with Whitney Cummings and check out new episodes of bananas every Tuesday on the exactly right network. Listen to bananas on the IHeart radio app, Apple Podcasts, or wherever you get your podcasts. York style pizza. Let's go and talk about yet another star in our galaxy. Which one are we talking about next, Daniel? So the biggest star that we know about is a star called Stevenson 218. This one has twice the radius of Beetlejuice, right? Beetlejuice already a thousand times the radius of the sun. This one's 2,100. And it's so big that it's so hot, it's 500,000 times brighter than the sun. Wow. Like, imagine 500,000 suns. in the sky, that's Stevenson 218. It's not kidding around. So how is it that I have heard of

Beetlejuice before, but I haven't heard of Stevenson 218? Beetlejuice is a star in the sky. It's a constellation. Stevenson 218 is much, much further away. It's like 19,000 light years away. So it's still in our galaxy, but it's like a completely different arm. So you can't really see it with the naked eye. It's something we're discovering. There's still a lot of uncertainty about what we know about it because it's so far away. But yeah, it's. It's a pretty dramatic star. And this is one of the things I love about astrophysics and astronomy is like, the more you look out in the universe, the more weird stuff you see that you can't explain.

You know, it's just like always a surprise when you build something new, which is why I think we should have like 10 times as many space telescopes as we do and ground telescopes and satellites and like, wow, think about the things we're missing in the universe just because we're not looking. That's right. And more money for fish research too. We're missing things. We could be looking all over the place. place, guys, and we're not looking enough.

More money for science. Let's build a space telescope that's excellent at finding alien fish on exoplanets. How about that? Is that a good compromise? Daniel, I am so glad we found something we can agree on. Yes, amazing. As long as those alien fish have alien parasites, I'm 100% in. And I bet they will.

All right. Excellent. I look forward to building that telescope with you. Okay. Slam dunk funding case for sure. They can't turn us down. All right, so let's focus away from fish, unfortunately. On to black holes.

All right. So let's go, you told us that some of the process for starting a star is similar to the process for starting a black hole. Remind me where those processes diverge, please. Yeah, so a lot of stars end up as black holes because fusion can't last forever, right? It's eating the stars, using the star as fuel. It's converting the light stuff into heavy stuff and eventually converts it into heavy stuff that it can no longer burn. Like our sun is hot enough to burn hydrogen. and near the end of its life,

it's going to be hot enough to burn helium very, very briefly. But anything heavier than that, our sun doesn't create the temperatures and the pressures and the densities to fuse. And so anything else that it makes is inert.

It interferes with the process of the star. And so that's why our sun, for example, is going to get a core that's basically dead. It's not participating in fusion anymore. And then fusions are going to move to outer layers of the star. And that's why the star puffs up

near the end of its life. You hear like, the sun is getting hot. and bigger, and in billion years, it's going to be really big. And that's true because the fusion is moving to the outer layers where there still is hydrogen. But eventually, the star accumulates so much heavy, inert stuff, stuff that can't participate in fusion, that the star collapses. Gravity wins, right? Eventually, fusion just peters out. And this collapse is really spectacular. You get this, like, pressure wave that goes into the star, and then it bounces back and comes out

and explodes the star. And that's where you get a supernova, right? It's like this shockwave that goes in and then out that travels at like incredible velocities, really violent stuff, really amazing. You sound like my daughter. She's really into violent stuff right now. She also sounds very excited when she's talking about explosions and stuff. Well, it's not that I want. Anybody start to blow up?

It's just the energy is just incredible. The numbers here are just mind-boggling. And then what happens at the core, the start depends on the amount of mass. So you get this really hot, dense thing left over. If it's not quite dense. dense enough, it can form a neutron star, which doesn't collapse into a black hole because there's something else pushing back now. It's not fusion pressure. Neutron star is a star, but there's no fusion happening. It's just electron degeneracy pressure. Like the particles that are in there, they're all

fermions, which means they don't like to be on top of each other the way electrons don't. And that effectively creates a pressure. Like they can't squeeze down and cool down into the lowest energy levels because they can't be in the same energy levels. And so they have to be in higher energy levels, which means they keep some energy. They move around. They basically push back. That's what degeneracy pressure is. People write in sometimes and ask like, what force is degeneracy pressure? Or like, why does the universe keep particles from entering the same state? You know, and there's no special force there. It's just that the particles cannot be in the same state. And so they stay in higher energy levels to avoid each other. And that creates pressure effectively. So a neutron star doesn't

collapse because of quantum mechanics. But, you know, eventually if you have enough mass, it can overcome that. It can push these things together so they're no longer really neutrons. Like they get smushed together and their neutronness sort of goes away as the quarks form this soup. And then the proto-black hole can collapse. So if you have enough pressure to squeeze those neutrons out of their fermion states and form a soup, you can form a black hole. And that's when you get above this critical threshold. Okay. So when we first started talking about fermions and you said that they don't like to be near each other the same way that electrons don't. I have been thinking about fermions as something that was kind of electron-adjacent. And I forgot that fermions are

more like neutrons. Well, fermions are a category of particle. All matter are fermions. Electrons, quarks, neutrons, protons, they're all fermions. And fermions have this particular property that you can't have two of them in the same quantum state, which is why electrons, for example, are not all in the lowest energy level around hydrogen. You have when the lowest energy level is filled, the next one can't be there. It's got to be in the next level, and then the next level, and then the next level. That's why electrons spread out on the ladder of energy levels, one per level. You know, there's like different spins you can have or whatever, but they all have to be in a unique state, which keeps the electrons effectively hotter, right? If the electrons could all

collapse into the lowest energy level, they would be cooler, but they're not, which keeps some electrons at high energy. And that's the same thing that's happening in the neutron star. The neutrons have to stay at higher energy because they can't collapse all into the lowest energy state. And that keeps the star hot and that keeps pressure going. Okay. And so when a big star collapses, presumably there's still fermions around. But what you said was that the black hole is so immense that it just squishes them down anyway and overcomes their desire to remain in happy states and push back out.

Yeah, exactly. Because neutrons are fermions because they're combinations of quarks. And so the rule still applies because you have fermions there. But if you squeeze those corks together, you can get other states that are, not fermions, and then it can collapse them, exactly. And the crucial thing to know for our later discussion is that when this collapse happens, you get a black hole, you get an enormous shockwave that comes out, right? This gravitational collapse produces an enormous shockwave, and a black hole heats up everything around it. The gravity of the black hole is really intense. The accretion

disc, the stuff around the black hole, gets heated up by the gravity of the black hole, and it radiates. This is why black holes are so hot, because they heat up everything around them, which then blows that stuff out. So like black holes is a limit to how fast they can grow in the universe because they emit so much radiation, they're pushing their food away from them. What? Yeah. The more massive they get, the more they heat up the stuff near them, which then blows the food away from them. There's no theoretical limit to the size of a black hole, but there's an effective limit to how quickly they can grow because they push away their food.

Baffling. This blows my mind. I can't understand that behavior. Yeah. And so these are normal stellar black holes, right? These are black holes that form at the end of the life of a star. And so we call these small black holes, even though they can be up to like 50 or 100 times the mass of the sun. Wow. But there's another category of black holes that we need to understand for today's episode, which are called supermassive black holes. That's a great song. And if I opened a Chicago pizza joint, I would call it super massive pizza.

Because these are definitely like a lot bigger. These are a few million to a few billion times the mass. of the sun. Wow. Like normal black holes, just 100 times, 50 times the mass of the sun. This is millions or billions of suns into a black hole. It's really incredible. So how do you go from an exploding star to something that's so much more massive than the star was initially?

Yeah, it's a good question. And people have been wondering about this in particular for a long time. And they asked exactly your question, and they did a bunch of simulations. They thought, well, maybe you have early galaxies with early stars and some of them form black holes and then those black holes clump together and they just gather together at the center which makes sort of sense and they ran simulations but those simulations do not describe what we see like in those simulations you do not get super massive black holes you get much smaller ones but when we look out into the universe we can look really far back in time at the formation

of supermassive black holes and ask how long did it take in the universe to form these black holes and it didn't take very long we see supermassive black holes at the hearts a very very very, very young galaxies much earlier than we expect. So they're like super massive black holes that are like 13 billion years old, which is like about a billion years after the universe began, you already have black holes with like two billion solar masses. Wow. Nobody knows how they got so big, so fast.

So is that the answer? Like we just, we don't know full stop? We don't know how supermassive black holes have formed. That is definitely a huge open question in astrophysics. There are lots of crazy ideas out there. One of them is the one I mentioned earlier, primordial black holes. People thought, hmm, maybe black holes formed in another special way, like in the early universe.

There were already black holes formed before even hydrogen. And so these guys were around to see the formation of supermassive black holes in the universe, perhaps. But nobody's ever seen a primordial black hole, and we should have seen one if they existed. So it's pretty hard to support that theory anymore. Although for a while, they were an exciting candidate for dark matter because, like, they're big, they're massive, they're dark, maybe they explain the missing matter. But, again, we haven't seen them and we should have. Another fun explanation for supermassive black holes came recently when people noticed that the rate of supermassive black hole formation, the rate of their growth, seemed to link weirdly with the dark energy in the universe.

That, like, the amount of dark energy in the universe is increasing, because the rate of the amount of dark energy in the universe is increasing, because the rate of the rate. the universe expands, and as it expands, it makes more space, then space comes with more dark energy. So the dark energy fraction is increasing as time goes on, just like the supermassive black hole mass is increasing. They noticed a very tight correlation. And they came up with this theory, which went everywhere on social media when it came out, like, last year or so, that maybe supermassive black holes are the source of dark energy,

that, like, weirdly, they're creating dark energy or they are expanding the universe somehow. It's not a theory that's really become mainstream. There's some questions and uncertainties about it. There's a whole podcast episode about it. You should check it out. But the point is that this is an open mystery. How do you get black holes that are this big, this massive in the early universe? So how we, how do, real quick, maybe you can just tell me.

So how does it get bigger and more massive while also creating more dark energy? Like, where is the energy for that coming from? You know what? I'll listen to the episode. You didn't do that episode with me, right? And I've forgotten the answer. was one with Jorge. Yeah, it's an episode I did with Jorge quite a while ago. It's a really fun idea, and there's two things to understand there. One is that we do have a theoretical model

for black holes, like we can solve the equations of general relativity for a black hole, but there's a detail that's often left out when people say that, which is that we only know how to solve these equations for a black hole in an empty universe. Like, we can solve the equations for a super dense object and nothing else, all right? But that's not our universe. And more importantly, our universe is expanding. So we don't know how to solve the equations for a black hole in an expanding universe or a universe filled with stuff. And so theoretically, there is a question mark there, like, how do black holes form an

expanding universe? What are those rules? We don't really know because we don't understand the solutions of general relativity. We basically only solved it for a very few simple cases, like a black hole in an empty universe or a universe filled with uniform dust. We can't even solve it for like the earth going around the size. Sun. That's too hard. Wow. What is it? All models are wrong, but some models are useful. Are they are these? These are still useful models, right?

GR is still useful and we can do numerical approximations a lot of times, but basically we don't understand how black holes form in expanding universe in theory. And so these guys have an idea for what's inside the black hole, that inside the black hole is not a singularity, but some weird vacuum energy that contributes to the expansion of the universe. And like, hey, that's possible. It's a violation of general relativity, but we know general relativity has to be wrong at some point. We don't understand how the expansion can be everywhere if it's sourced from the black holes. So there's a lot of open questions about that. Black holes also are really big and massive, but they're a tiny fraction of the mass of the universe, whereas dark energy is like

70% of the energy in the universe. So this doesn't really answer that. But the point is that we still don't understand how supermassive black holes form, but they are out there in the universe. So there's another really crazy and exciting theory that we'll talk about after the break that might tell us what was inside even bigger stars than we can imagine. Have you ever wished for a change but weren't sure how to make it? Maybe you felt stuck in a job, a place, or even a relationship. I'm Emily Tish Sussman, and on she pivots, I dive into the inspiring pivots of women who have taken big leaps in their lives and careers. I'm Gretchen Whitmer, Jody Sweeten.

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Listen to these women and more on She Pivotts, now on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. The U.S. Open is here, and on my podcast, Good Game with Sarah Spain, I'm breaking down the players from rising stars to legends chasing history. The predictions will we see a first time winner and the pressure. Billy Jean King says pressure is a privilege, you know. Plus, the stories and events off the court and, of course, the Honey Deuses, the signature cocktail of the U.S. Open. The U.S. Open has gotten to be a very fancy, wonderfully experiential sporting event. I mean, listen, the whole aim is to be accessible and inclusive for all tennis fans, whether you play tennis or not. Tennis is full of compelling stories of late.

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We feel sometimes like we're leaving a part of us behind when we enter a new space. but we're just building. On a recent episode of Culture Raises Us, I was joined by Volusia Butterfield, media founder, political strategist, and tech powerhouse for a powerful conversation on storytelling, impact,

and the intersections of culture and leadership. I am a free black woman who worked really hard to be able to say that. I'd love for you to break down why was so important for you to do, see you. You can't win as something you didn't create. From the Obama White House to Google

to the Grammys, Melisha's Journey is a masterclass in shifting culture and using your voice to spark change. A very fake, capital-driven environment and society will have a lot of people tell half-truths. I'm telling you, I'm on the energy committee. Like, if the energy is not right, we're not doing it, whatever that it is. Listen to Culture raises us on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Hi, I'm Kurt Brown-Oller. And I am Scotty Landis, and we host Bananas, the Weird News Podcasts with

Wonderful guests like Whitney Cummings. And tackle the truly tough questions. Why is cool mom an insult, but mom is fine? No. I always say, Kurt, it's a fun dad. Fun dad and cool mom. That's cool for me. We also dig into important life stuff.

Like, why our last names would make the worst hyphen ever. My last name is Cummings. I have sympathy for nobody. Yeah, mine's brown-oller, but with an H. So it looks like brown-holer. Okay, that's, okay, yours might be worse. we can never get married. Yeah.

Listen to this episode with Whitney Cummings and check out new episodes of bananas every Tuesday on the exactly right network. Listen to bananas on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. All right. We're back, and it's time for the big payoff. Could black holes be inside of a star? Daniel? So we talked about how stars form, and the crucial thing to remember there is that stars can't get too big because they blow out their stuff. And if a black hole forms, it blows stuff away from it also. And then we talked about how we don't understand how supermassive black holes formed in the universe. So the idea is bring these two things together and say, what if there was a special kind of star in the early universe?

that was so big, so massive, that it formed a black hole at its core, which ended up being the seed for a supermassive black hole, and so big that it was protected against that shockwave of blowing stuff out. Ah. So it would just be a star until the black hole took over. So let's walk through the lifecycle of it, because it's kind of crazy and kind of a fun theory. So you start in the very early universe, just like we talked about before. Everything is very dense.

Everything is very hot. And, you know, we have areas of over-density that are pulling stuff in. Something I should have mentioned before, which I think is super cool, is that it's not just over-densities in the normal matter, not just like, oh, here's a little bit more hydrogen. It's actually over-densities in the dark matter that are really important. Because remember, dark matter is the dominant source of matter in the universe. That's most of the matter. So if you happen to have a clump of dark matter, then the normal matter is going to get pulled

towards that. So dark matter actually controls where normal matter forms structure. Sure. You can think of it that way or the other way, which is like normal matter tells us where the dark matter is. It's like tracers. So if you look at it in the night sky and see a bunch of stars, you know, oh, there's probably a big blob of dark matter there. That's why stars formed there. Anyway, that's super cool. But in the very early universe, we didn't have metals to form these stars, right? So you have either an over density of hydrogen or an over density of dark matter pulls this stuff together. You get super massive short-lived stars. And in the standard theory, remember that if it gets too big, it gets too big, it gets too hot and it blows that stuff away. But if the star is big enough, like really enormous, not 300 times the mass of the sun, not a thousand times the mass of the sun, we're talking millions of times of the mass of the sun. If you happen to get a blob of stuff together from a dark matter over density and then try to collapse that gravitationally, the idea is maybe something special happens at the core of the star and the star's mass protects it against the

radiation that's coming out because gravity is just so overwhelmed. And it becomes a black hole? Yes. And so what happens is you have this huge blob of stuff. We're talking about like a million times the radius of the sun, right? So like blow your mind trying to hold this thing in your head. The core gets hotter and gets denser, just like we talked about before. But now there's enough gravitational pressure to turn the core into a black hole.

So you have this enormous star. And at the heart is this tiny but very, very dense black hole, like a few tens of a kilometers across. How cute. how cute but terrifying that's right now normally when you form a black hole or you have this gravitational collapse at the core you would get a shockwave that would like tear the star apart right that's what supernovas are in general but this one is so massive that the shock wave just like it just gets absorbed right it doesn't get all the way to the outside the outside layers are squeezing back in it's like you know a violent crowd or an english football game or something you know squeezing back in and so

something else happens, the outer layers of the star that are squeezing the gas are forcing it into the black hole. Usually black holes can grow only kind of slowly because they're pushing their food away, right? Well, what if there's like a huge blob of gas on the outside forcing it back? So now it's being force-fed gas, even though the radiation pressure is pushing it away. So now your black hole is growing pretty quickly as it's like being forced-fed gas at the heart of this star. So yes, it is a star, and there's a black hole at its core. And the thing that keeps it from blowing apart is its sheer mass.

It's too big to collapse. Holy cow. I'm impressed. Okay, so it seems to me that this process should pretty quickly result in the star becoming a giant black hole. Is that the point you can get black holes forming in the center of stars

before they're at their end of their life and it hastens the end of the life of the star? Yeah, so eventually this thing will collapse. It can't last forever. Okay. It's got a pretty good run, though, for the few moments in the universe's history that it glows. Like, it's super duper bright. You know, we talked about fusion happening more rapidly at high temperatures and pressures.

So this one single massive star with the black hole core would have been about as bright as the entire galaxy. Wow. So, like, really incredible. Essentially, as bright as a supernova. Supernova is also as bright as a galaxy. And so the black hole is growing. The star is expanding. Right.

Eventually, the whole thing becomes 30 times the way. width of our solar system. Wow. So we were talking beetle juice is like the orbit of Jupiter. Wow, that's big. Yeah, this thing is monstrous compared to that, right? And then you get magnetic fields, which create radiation and quasars, just like we talk about. But eventually, the black hole grows so much that it will tear the star apart because the radiation pressure from the black hole is pushing out. And that will eventually take over because there's only so much star to eat. And the thing that was keeping this stable was the outer layers of the star. The more you eat the star, the less protection you have. Bad idea. It's like you're eating your own spaceship, right? So it only lasts like

10 million years or so in the early universe. But what's left over is a very massive black hole, much more massive than you would expect from the death of a normal star. And if you have a very massive black hole around and other stars are forming nearby, you could imagine that they would start orbiting that really massive black hole. And it could end up being the center of a galaxy. Okay, so we've seen supermassive black holes, but we have not seen this in the process of happening because this would have happened so long ago. Could we still see this happening super far away or this happened so long ago that that light would have already passed us or something? Great question. We're going to take away my POD and physics. No, POD and physics

comes from asking sincere and curious questions about the universe. It's not about being right. Okay. So never want to discourage somebody from thinking. And that's physics, right? What you're doing right there is physics. You're like, this is what I understand. This is what you're telling me.

How do I fit it together and do a model in my head? That's the essential step of doing science. And so, yeah, absolutely. You earned your PhD twice over. Yay. The answer is, if it happened in the early universe, we should be able to see it because we can just look further and further away. Because if it happened a long time ago, we just need to look at life that's been traveling

since then, which means it's gone a really long distance. And we can see pretty far back. We can't see all the way back to that far in the universe. The James Webb Space Telescope can see, like, formation of young galaxies, and that's helping us understand the supermassive black hole question, but we can't, with the James Webb, see that far back yet. But in principle, we could be able to, right? These things would have been very bright, even though they're super far away we might be able to make them out. Your other comment is, like, would the light from them have past us. That's true for some of them. Like if there was one of these things in the heart of our galaxy and it emitted a bunch of light, its light would now be too far away for us to see.

But the universe just goes on and on and on. And so there's always some more universe to send us light that's just arriving now. So that's why we can see the whole history of the universe from here if we look further and further away. So the theme of today is Fund More Telescopes. Yes, exactly. Fun more telescopes. Because there are deep mysteries here about how stars form and how matter works. And, you know, this is a fun theory because it makes you think about huge stars and stars with exotic cores in them and maybe something else is happening at the hearts of stars or whatever. And because it solves a mystery, but probably the answer is something else, something even we have imagined. And so, you know, it's a useful exercise in physics to be

like, what about this? What about that? Could this even work? Very valuable. But it's also just a useful exercise to go out and look, you know, to ask the universe, tell us, show us what's going on out there. And then we got to piece that together into our puzzle of how the universe works and maybe have one of those moments of insight where we're like, oh, I get it. And it clicks into place and you're like, yeah, universe, you make sense to me. It's so nice to have those moments with your partner. It's nice to have those moments with your universe as well. Do you have a similar relationship with the universe as you do with Zach? Both of them surprise me from time to time, you know? No, life should keep you on your toes.

I hope you keep building husband telescopes so you can keep observing new surprises in your relationship. Well, my training was an animal behavior, so I'm always collecting data. I mess with him every once in a while. I'll do things like, see how close I have to put the laundry bin to, like, where he always throws the clothes on the floor before they'll actually end up in the bin. Like, will he throw it if it's just an inch out of where he usually throw it? Anyway, I digress. Do you need an IRB? to do experiments on your husband like this?

Well, you know, I'm not really in academia right now. And so don't tell Rice. Okay. So was I going to ask? We were talking about the black hole of Zach's laundry. Oh, God. That's actually a different topic. But, okay.

We're supposed to keep this family friendly. All right, all right. I'm back on track. I'm back on track. Okay. So you hear this theory that you've just presented to us. Do all the steps in this theory sound good to you? Does this sound plausible?

You said that it's probably something else just because the universe is hard to figure out. But is there any step in this process that makes you feel like, oh, I don't know, maybe not. There's nothing about this that's obviously wrong. There's no red flags. But there is a lot of speculation here. You know, there's like, well, maybe this can survive that and maybe this happens and it gets force-fed. But it's complicated. Like, what you would really need to do is to model this and not just be like, well, my intuition says it's probably correct.

you need to see what did actually happen and put this thing into a computer. But that's hard. You know, we have trouble modeling individual stars turning into black holes and going supernova because you need to keep track of so many particles and they're very sensitive to the details. We don't really understand like, why does this star go supernova and that one doesn't? It's not just a function of the mass. Like it requires some special circumstance to happen or to not happen.

And so there's probably just a lot of that, a lot of details that need to be filled in. And it's a lot of work. So we should not only build new telescopes, we should hire more scientists and give them lots of computers. Yes, amen, because you've got to start somewhere. And ideas like this help you identify the assumptions that you need to be testing in order to move forward. So, yeah, very cool idea. And if you discover, oh, this doesn't work, it's going to give you another idea. And that's how we make progress.

Yep. Right? Start out with terrible ideas that inspire less terrible ideas. Yeah. Dot, dot, dot, science. Yeah, I think the answer to my Ph.D. work was, no, Kelly was wrong. But here's some other interesting stuff you could ask. Exactly.

It's always fun follow-up questions. That's right. And on that note, if you have follow-up questions from today's episode or anything else you've heard about in physics, please write to us. We would love to answer your questions. Physics, biology, maybe even chemistry once in a while. Pizza-related questions? Definitely, absolutely pizza-related, especially the physics of pizza. No, I guess pizza's mostly chemistry, isn't it?

Anyway, write to us questions at Danielandkelly.org. We love hearing from you. We really do, and we really will write you back. Enjoy your pizza. Daniel and Kelly's Extraordinary Universe is produced by IHeart Radio. We would love to hear from you. We really would. We want to know what questions you have about this extraordinary universe.

We want to know your thoughts on research. shows, suggestions for future shows. If you contact us, we will get back to you. We really mean it. We answer every message. Email us at questions at danielandkelly.org. Or you can find us on social media. We have accounts on X, Instagram, Blue Sky, and on all of those platforms, you can find us at D and K Universe. Don't be shy. Write to us. Why are TSA rules so confusing? You got a hood of your take it all! I'm Mani.

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You know, lock him up. Listen to No Such Thing on the Iheart radio app, Apple Podcasts, or wherever you get your podcast. No Such Thing. Welcome to Pretty Private with Ebeney. The podcast where Sound. is broken and stories are set free. I'm Ebeney, and every Tuesday I'll be sharing all new anonymous stories that would challenge

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