Short Wave - The Curious Case Of The Supermassive Black Hole

Episode Date: July 30, 2024

Black holes are one of the most mysterious cosmological phenomena out there. Astrophysicist Priya Natarajan calls them "the point where all known laws of physics break down."On the list of perplexing qualities: The origins of supermassive black holes. That story was only confirmed within the last year. Check out more of our series Space Camp on the weird and mysterious in space at npr.org/spacecamp.Interested in more space science? Email us at [e-mail] to Short Wave on Spotify and Apple Podcasts.See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Hey, Shortwavers. It's Space Camp First Officer Emily Kwong here. And today, we're investigating one of our most mysterious cosmological phenomena out there, black holes. It's like the point where all known laws of physics break down. Priya Natarajan is an astrophysicist at Yale University, chair of the astronomy department, and she was named one of times 100. most influential people, all because of her boundary pushing work on black holes. So for me, the personal attraction, the gravitational pull, pun intended, toward black holes,

I mean, really is that they kind of represent the limits of knowledge. I first spoke with Priya in 2020, and she explained to me that the discovery of black holes first happened on paper through Einstein's math equations. He described the universe as like a four-dimensional fabric. fusing space and time. And the fabric is bumpy, dotted with planets and other kinds of matter. And what matter does, it causes little potholes in these issues. You drop mass somewhere, you create a pothole.

And Einstein's peers wondered, okay, well, what happens when you have an object whose mass is so compact that the pothole becomes a puncture in the fabric of space-time itself? And so the black hole solution is one of the simplest solutions to these very very, complex equations. This theory of black holes was eventually confirmed in 1964. But it set up another mystery, which is how do black holes even begin? For a long time, scientists were only sure about one origin, that black holes were created through the collapse of a dying star. But that didn't fully explain how supermassive black holes came to be. Their origin story was only confirmed in the last year.

Today on the show, Black Holes Reimagined. First, we venture on a mind-bending journey into a black hole, where the laws of physics breakdown, and then Priya shares this alternate origin story, which has transformed our understanding of the early universe. I'm Emily Kwong, and this is Shortwave from NPR. We're talking with Priya Natarajan, an astrophysicist at Yale and our Black Hole guide.

First of all, right, let me just sort of clarify, right, there are different kinds of black holes. So there are black holes that are stellar mass black holes. Intermediate mass black holes, supermassive black holes, and ultramassive black holes. And each black hole, at least mathematically, has a kind of boundary called the event horizon. That is the region that encloses that puncture in space time. And this puncture is technically called a singularity. That's the black hole. And what is special about this event horizon is that any option, that crosses the event horizon, it's the point of no return. Because that is the region within which the grip of gravity of the black hole is such that you have nowhere to go but in. You get sucked in.

And what if a person were to fall into a black hole? What would they see and experience? Right. So the, okay, so the first thing that one... Not that I want to do that, but as a thought experiment. It is not a fate. It is not a fate that you want to actually experience. So it's going to matter if you are going to fall into a stellar mass black hole or a supermassive black hole. A stellar mass black hole, the pothole is dramatically deeper because it's so much more compact. So if you are falling into a stellar mass black hole, then say you're diving in head first, right? So your hair is hanging down. So the difference in the strength of gravity between your hair and the tips of your toes would be. so strong that the gravity would rip you apart. It would stretch you out into a spaghetti. It's called spaghettification.

It's a technical term. It's called spaghettification? Yes. And so you would be like stretched out, painfully stretched out, right? And of course no one can hear you scream once you cross the event horizon. So that would be your fate. Whereas in a supermassive black hole, it's a slightly gentler, horrific end.

So once you fall into the event horizon, as you are approaching the event horizon, you would be able to see the entire universe around you. You'll be able to see all the stars, the light from the stars, except you would start to see the sort of multiple copies of the universe outside, and you would see them kind of inverted.

You'd see all these effects. The extreme light bending effects are called gravitational lens. and then it would all become black. And then you would experience something that is really weird. So one of the things that happens once you cross the event horizon is the role of space and time kind of switch. So you will be actually falling in time rather than space. And what that really means is that every direction, any direction, back,

front, right, left, you would be hurtling towards the singularity. It's really super disorienting. So when you're being spaghettified as you're falling through a black hole. Stellar mass black hole. Yeah. The stellar mass black hole. You're moving through the space time, the fabric of the universe. The fabric has now switched. Ah. So when you're falling past the event horizon and you have been spaghettified, then you are hurtling, towards the singularity, which is this point where all laws of physics breakdown, that is the puncture in space time.

So that's the other way of thinking about black holes. Space time would be extremely curved once you have passed the event horizon. And in fact, it won't really be space time as it is outside the event horizon, because here the nature of space and time swap. And so you're kind of falling in time. time as it were, rather than space. We, of course, don't have data on this, as you can imagine. No human has fallen through time.

But what would it mean to fall through time? Yeah, you know, I can think of like a different sense of what happens to time in the gravitational field of an object. So, you know, time actually slows down when you are in an intense. gravitational feel. So an experience of a difference in the flow of time. Well, it's kind of a moot point, like, how are you experiencing it? Because, you know, I think by then all your cells would have stopped functioning and you would be clinically dead. Couldn't experience anything. That's right. But this idea is that... You just cannot escape the grip of the gravity. You cannot escape. And it's an infinite fall as you're falling towards the singularity. Absolutely. And this infinite

fall would be experienced in the flow of time as really slowed down. Yes. So it's like a stretching out slowing down. That's right. The other sort of peculiar way in which it would manifest is that the, you know, the friend who was waiting outside and let you sadly fall into the black hole, their clock and your clock would no longer be synchronized, right? Because your clock would have slowed down enormously. Wild. So recently, scientists have been able to figure out even more. more about black holes. Priya, the first time we talked, you explained to me how stellar mass

black holes are thought to have originated from dying stars. These are smaller black holes. But that origin story need not work for supermassive black holes. So why is that? Like, what was the traditional explanation and why did it not work? The traditional explanation is that you have a first generation of stars that were supermassive, that were probably heavier than the stars that we see forming around us now today, they would still be only about 100, maybe 50 to 100 times the mass of the sun. So to form a supermassive black hole, which is a million times a mass of the sun, you would have to grow a lot. It turns out, however, that there was a bit of a timing crunch. There's just not enough time to grow that much. So we came up with an alternative. We proposed

theoretically an alternative almost 20 years ago. now. And the other way was gas. You proposed that a huge cloud of collapsing gas created the seed of a supermassive black hole. Yeah. It was pretty rad. So it took us, of course, a long time to figure this out, right? Took us several years to really understand how this happens. But essentially the idea is that when you have a galaxy very early in the universe, before it forms stars, right, stars form out of gas. So the gas settles down into a disk. And then this disk of gas can just become unstable. You know, much like the vortex that forms when you pull the plug in your bathtub

and the water really rushes in really fast, something similar happens in the early universe, and all of that gas can siphon in very quickly to the center, and it could form a very massive seed. The start of a heavier seed that would then grow into a supermassive black hole. Right. They could start life right away from birth, be already

thousand, 10,000, maybe even 100,000 times the mass of the sun to start with, which then makes it easy to easy to just grow to a million times the mass of the sun. Which also solves the timing problem. It means brilliant. Okay, so you propose this

in 2006. Decades pass. It's all just theoretical, this idea. But then along comes the James Webb Space Telescope, and that telescope and the Chandra X-ray Observatory, found this very distant, very young galaxy called UHC1, with a supermassive black hole at the center that began just the way you theorized

through this cloud of collapsing gas. How did it feel to finally have the proof of it all these years later? I literally fell off my chair. Yeah. As a theorist, right, you propose these ideas, you are excited about, them, right? I mean, we published these papers like 20 years ago. And so, you know, it's 20 years, I mean, it felt like a long time, but, you know, in the grand scheme of things, it's not a long time. And yeah, I mean, and I just, you know, we couldn't believe that almost every aspect, right? It matched

every one of them. What did it reveal a new for you about black holes and how they work? I think what was for me kind of revealing about this discovery, and the validation is that, you know, nature really does make black holes in a lot of different ways and that they're definitely therefore not marginal. Like we always thought, you know, they were peculiar and they were kind of marginal bit players in the cosmic drama, but they're not. So, you know, we are increasingly seeing that they're starting to play a starring role, right? Yeah.

I think now it is impossible to come up with a deep and clear. understanding of how, you know, our universe was structured, how the galaxies formed and grew and evolved over cosmic time without taking black holes into account. Yeah, they have that main character energy. And you've been one of their number one champions. That's right. Priya Natarajan is an astrophysicist at Yale University, where she studies black holes and dark matter. Just a reminder, we will be back tomorrow with more regular shortwave and back Tuesday with our next installment of the space camp series, which features not just one, but two experts.

Hey, Shortwave, it's Chandra Prescott Weinstein and Renee Lajick. We're your experts in space theory and in practice. We're tuning in to remind you that regardless of where you are, you're swimming in the light juice left over from the Big Bang. And based on our measurements of that Big Bang juice, the scientific name for it is the cosmic microwave background. We're learning more and more about the early era of our universe. Big Bang Juice. I'm intrigued. All right. Well, tune in next week, everyone. Our original Black Hole's episode was produced by Rebecca Ramirez

and edited by Viet Le and fact-checked by Emily Vaughn. This space camp version was produced by Hannah Chin and Rachel Carlson. Regina Barber, Hannah, and I checked the facts. Julia Carney is our space camp project manager. Beth Donovan is our senior director. And Colin Campbell is our senior vice president of podcasting strategy. Special thanks to our friends at the U.S. Space and Rocket Center. home of space camp.

I'm Emily Kwong. Thank you for listening to Shortwave from NPR.