NPR’s Danielle Kurtzleben speaks with astrophysicist Priyamvada Natarajan about the James Webb Space Telescope’s recent discovery of two distant black holes colliding.
DANIELLE KURTZLEBEN, HOST:
The James Webb Space Telescope is wowing us once again with a new discovery that redefines how we understand the origins of the galaxy. New images show a collision of two huge black holes, and it is the most distant black hole merger ever detected. The collision occurred just 740 million years after the Big Bang that shaped the universe. And to talk about it, we have someone who lives and breathes black holes. Priyamvada Natarajan is an astrophysicist and chair of the Department of Astronomy at Yale University. Priya, welcome.
PRIYAMVADA NATARAJAN: Thank you very much. Glad to talk to you about black holes.
KURTZLEBEN: Well, great, because we’re going to start with the absolute basics. So remind us what a black hole is, and why is it important that we spotted the merger of two of them?
NATARAJAN: So a black hole is – you can think of it, you know, in many ways, but one important way – a simple way of thinking about it is a special place in space, where a lot of matter is concentrated. And it’s so highly concentrated that it sort of distorts the shape of the space-time fabric in which it sits. So we’re all immersed in space-time, right? – the entire universe is embedded in this four-dimensional sheet, and all matter causes a small hollow in this type of tissue, which is actually four-dimensional, but we can think of it simply as tissue. But what a black hole actually does is cause a puncture in space-time. So this is a very dramatic transformation of the shape of space. And that’s because the matter is concentrated in a really, really small space. It’s really dense and compact.
The exciting thing about black hole mergers is that we know that black holes are virtually everywhere, and there is one at the center of our own galaxy that is 4 million times the mass of the sun . The big questions are therefore: what is their origin? How were they born? And James Webb opens the early universe. We have these new eyes in the early universe, and we see that galaxies – very, very old galaxies – already have supermassive black holes hidden in the centers of these galaxies, already when the universe was barely several hundred million of years. And we don’t know how these black holes are born or how they develop. Mergers are therefore seen as a means of growth. The other is just a guzzler of gasoline.
KURTZLEBEN: I want to make sure we know the scope of this here. We talked here about supermassive black holes. That’s the word used in all of these articles. What size are we talking about?
NATARAJAN: A million times the mass of our sun…
KURTZLEBEN: Oh.
NATARAJAN: …That’s often what we refer to.
KURTZLEBEN: Yeah. Maybe describe to us what this collision looks like in these images.
NATARAJAN: Well, the collision, actually, based on our current understanding, is extremely complicated and messy. And this picture is also very complex. I mean, you see them as little dots, obviously, because it’s very far away, so you don’t see the well-formed galaxies that we know in the nearby universe. These are sort of little spots. But what’s cool about this particular sighting is that they have a spectrum.
The spectrum therefore corresponds to the energy emitted by the stars and the growing black hole captured by James Webb. And in this spectrum, there are very clear signatures that show that there are probably two black holes. One of them is sort of glowing, so you can see a clear signature. The other seems enveloped in dust. So it’s very complicated, a little complicated, but, you know, very exciting. It’s like fireworks but a little complicated.
KURTZLEBEN: I wonder if you can tell us what happened in that collision, sort of the play by play before, during and after.
NATARAJAN: That’s true. So it’s very likely that this one is just an example, but it adds credence to our understanding that black holes also grow by simply crashing into each other. So probably what happened was that in a very dense environment, there were two galaxies, each housing a central black hole that came very close and sort of danced a little bit before collapsing. crush with full force. Once they crash head-on, these two black holes will likely end up being buried in some kind of disk of gas dust, a messy disk. And they started kind of banging against each other, kind of, you know, slowly going around in circles in a dance, and they were getting closer and closer.
And eventually, they would completely collapse and crash into each other. And when they do that, they shake up all of space-time. So you have tremors in spacetime, gravitational waves that are generated when they eventually merge with each other. Right now we are witnessing the dance beforehand. And that’s when you have all these other fireworks. Like I said, you see the spectrum. You see all these signatures. So you see signs before the final frontal collision. We have therefore not yet witnessed the final head-on collision, but it is inevitable. This is going to happen, and we expect the final merger, as it’s called, to happen within the next few hundred million years.
KURTZLEBEN: Does all this mean that the crash has already happened and we will see it in the years to come, or that it has yet to happen – it is happening?
NATARAJAN: Yeah. The crash has happened – in the context of black holes, the crash has already happened.
KURTZLEBEN: Yeah.
NATARAJAN: It’s going to take us a while to witness this – right? – because of the speed of light and its distance.
KURTZLEBEN: Fascinating. So I’m curious. You study black holes for a living, so this must be a pretty big time for you. What of your biggest questions does this help answer?
NATARAJAN: The big open question is how do they grow. So this observation sort of supports the theoretical picture that people like me have been conjecturing for a long time, that the growth of black holes happens in two ways, a sort of accretion, i.e. gas absorption, the technical term is the accretion of gases, and crashing into each other. So we also expect that in the early universe, which was dense, many 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 watch next? What are your new questions?
NATARAJAN: So the new questions, of course, are, you know, how often does this happen – that’s just one thing. So we want to see how often mergers can occur. And like I mentioned, right? – the final stage of this merger, of this crash, is that you end up with a big black hole, and you cause 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 occurred in space-time, these gravitational waves. So I think it’s quite tempting, is to open the window and say, hey, these are the types of objects that hopefully will be ubiquitous and that LISA will see.
KURTZLEBEN: Priyamvada Natarajan is an astrophysicist and chair of the astronomy department at Yale University. Priya, thank you very much for your time.
NATARAJAN: Glad to have been able to talk to you about black holes.
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KURTZLEBEN: Before we go, a preview of a story coming 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 the number of patients receiving care. Some are opting for telehealth appointments to access abortion medications.
UNIDENTIFIED PERSON: In my situation, I felt more comfortable than in a doctor’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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