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New images show a black hole collision


The James Webb Space Telescope is blowing our minds once again with a new discovery that's redefining how we understand the origins of the galaxy. New images show a collision of two enormous black holes, and it's the most distant black hole merger ever detected. The collision happened just 740 million years after the big bang event that shaped the universe. And with us to talk about it is someone who lives and breathes black holes. Priyamvada Natarajan is an astrophysicist and the chair of the astronomy department at Yale University. Priya, welcome.

PRIYAMVADA NATARAJAN: Thank you so much. Delighted to be talking to you about black holes.

KURTZLEBEN: Well, great, 'cause we're going to start with the absolute basics. So remind us what a black hole is, and also why is it important that we've spotted a merger of two of them?

NATARAJAN: So a black hole is - one can think of it, you know, multiple ways, but one important way - easy way to think about it is a special place in space, where there's a lot of matter that is concentrated. And it is so strongly concentrated that it kind of warps the shape of space-time fabric in which it is sitting. So we are all embedded in space-time - right? - the entire universe is embedded in this four-dimensional sheet, and any matter causes a little divot in this sort of fabric, which is actually four-dimensional, but we can think of it just as a fabric. But what a black hole does is actually cause a puncture in space-time. So it's a very dramatic transformation of the shape of space. And that's because matter is concentrated into a really, really tiny space. It's really dense and compact.

So what's exciting about the mergers of black holes is we know that black holes are essentially everywhere, and there's one in the center of our own galaxy that's 4 million times the mass of the sun. So the big questions are, what is their origin? How did they come to be? And James Webb is opening up the early universe. We have these new eyes in the early universe, and we're seeing that galaxies - very, very early galaxies - already have supermassive black holes lurk in the centers of those galaxies already when the universe was barely several hundred million years old. And we don't know how these black holes actually are born and also how they grow. So mergers are believed to be one way by which they grow. The other is just gobbling of gas.

KURTZLEBEN: I want to make sure we know the scope of this here. We've talked about supermassive black holes here. That's the word that's used in all of these articles. How big are we talking?

NATARAJAN: A million times the mass of our sun...


NATARAJAN: ...Is often what we refer to.

KURTZLEBEN: Yeah. Maybe describe for us what that collision looks like in these images.

NATARAJAN: Well, the collision, actually, from our current understanding, is extremely messy and complicated. And this image also is very complex. I mean, you see them as little dots, obviously, because it's really far away, so you're not seeing, like, well-formed galaxies that we're familiar with from the nearby universe. They're sort of little blobs. But what is cool about this particular observation is they have a spectrum.

So the spectrum is that the energy that is emitted by the stars and the growing black hole that James Webb captures. And in that spectrum, there are very clear-cut signatures that show that there are likely two black holes. One is kind of popping, so you can kind of see a clear signature. The other one looks like it's enshrouded by dust. So it's a very messy, kind of complicated, but, you know, very exciting. It's like fireworks but kind of messy.

KURTZLEBEN: I wonder if you can tell us what happened during this collision, sort of the play-by-play of before, during and after.

NATARAJAN: Right. So most likely, this particular - it's only one instance, but it is adding credence to our understanding that black holes also grow by just crashing into each other. So probably what happened is in a very dense environment, there were two galaxies, each harboring a central black hole that came really close and kind of danced around a little bit before kind of crashing head-on. Once they crash head-on, these two black holes would likely end up being embedded in a gas dust sort of disc, a messy disc. And they would be starting to sort of pummel towards each other, sort of, you know, slowly circling in a dance, and they get closer and closer.

And eventually, they would completely collapse and crash into each other. And when they do that, they shake entire space-time. So you have tremors in space-time, gravitational waves that are generated when they finally kind of merge with each other. Right now we're seeing the dance beforehand. And that's when you have all these other fireworks. As I said, you see the spectrum. You see all these signatures. So you see signposts before the final head-on crash. So we have not yet seen the final head-on crash, but it's inevitable. It's going to happen, and we expect that the final, you know, merger, is what it's referred to, will happen in the next few hundred million years.

KURTZLEBEN: Does this all mean that the crash already happened and we'll just see it in the next years, or it still has to - it is coming about?

NATARAJAN: Yeah. The crash has - in the frame of the black holes, the crash has already happened.


NATARAJAN: It's going to take us time to actually witness it - right? - because of the speed of light and how far away it is.

KURTZLEBEN: Fascinating. So I'm curious. You study black holes for a living, so this must be a pretty big moment for you. What of your biggest questions does this help answer?

NATARAJAN: The big open question is how do they grow. So this observation really kind of lends support to the theoretical picture that people like me have surmised for a long time, that black hole growth occurs through two ways, sort of accretion, that is, the gobbling of gas, the technical term is accretion of gas, and by crashing into each other. And so we also expect that in the early universe, which was dense, a lot of objects were closer than they are today, so collisions were more frequent. You know, it's a clue that, hey, this picture, this emerging picture, and the theoretical ideas that we had are sort of validated.

KURTZLEBEN: Well, now that you have this new information, what are you going to be watching next? What are your new questions?

NATARAJAN: So the new questions, of course, is, you know, how frequently do these - this is just one object. So we want to see how frequently mergers can happen. And as I mentioned - right? - the final stage of this of this merger, of this crash, is you end up with one big black hole, and you set up tremors in space-time that we don't yet have the equipment to detect. But, you know, the European Space Agency and NASA are collaborating on a space mission called LISA that will actually measure the tremors that have been set up in space-time, these gravitational waves. So I think this is kind of tantalizing, it's opening the window and saying, hey, these are kinds of objects that are going to be hopefully ubiquitous that LISA is going to see.

KURTZLEBEN: Priyamvada Natarajan is an astrophysicist and the chair of the astronomy department at Yale University. Priya, thank you so much for your time.

NATARAJAN: Delighted to have been able to talk to you about black holes.


KURTZLEBEN: Before we go, a preview of a story coming up tomorrow on All Things Considered. Nearly two years after the Supreme Court overturned Roe v. Wade, a lot has changed when it comes to abortion access, including how many patients are receiving care. Some are opting for telehealth appointments to access abortion medication.

UNIDENTIFIED PERSON: In my situation, I felt more at ease than I would in a physician's office. And more comfortable, to be honest.

KURTZLEBEN: Our series, We, The Voters, continues tomorrow with a look at how abortion access is changing across the country and how that's motivating voters this election year.

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