New images show a collision between black holes

NPR’s Danielle Kurtzleben speaks with astrophysicist Priyamvada Natarajan about the James Webb Space Telescope’s recent discovery of two distant black holes colliding.


The James Webb Space Telescope is wowing us again with a new discovery that redefines the way we understand the origins of the Milky Way. New images show a collision of two massive black holes, and it’s the most distant black hole merger ever observed. The collision occurred just 740 million years after the Big Bang 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 chairman of the astronomy department at Yale University. Prija, welcome.

PRIYAMVADA NATARAJAN: Thank you very much. I’m glad I could 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 noticed a merger of two of them?

NATARAJAN: So a black hole is – you can think of it in several ways, but one major way – the easy way to think about it is a special place in space where a lot of matter is concentrated. And it is so highly concentrated that it slightly distorts the shape of the space-time fabric in which it resides. So we’re all embedded in space-time, right? – the entire universe is embedded in this four-dimensional sheet, and any matter causes a small gap in this kind of tissue, which is actually four-dimensional, but we can just think of it as a tissue. But what a black hole does is essentially create a leak in space-time. So it’s a very dramatic transformation of the shape of the space. And that’s because matter is concentrated in a very, very small space. It is really compact and compact.

The exciting thing about black hole mergers is that we know that black holes are essentially everywhere, and that there is one at the center of our own galaxy that has 4 million times the mass of the Sun. So the big questions are: what is their origin? How did they originate? And James Webb unlocks the early universe. We have these new eyes on the early universe, and we see that galaxies – very, very early galaxies – have had supermassive black holes lurking in the centers of those galaxies since back when the universe was just a few hundred million years old. And we don’t know how these black holes actually form and also how they grow. So it is believed that mergers are one of the ways in which they can grow. The other just drinks gas.

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

NATARAJAN: A million times the mass of our sun…


NATARAJAN: …Is what we often refer to.

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

NATARAJAN: Well, the collision is, according to our current understanding, extremely messy and complicated. And this picture is also very complex. I mean, you obviously see them as little dots, because it’s very far away, so you don’t see the well-formed galaxies that we know from the nearby universe. They’re kind of like little spots. But the nice thing about this particular observation is that they have a spectrum.

So the spectrum is the energy emitted by the stars and the growing black hole that James Webb captures. And in that spectrum there are very clear features that show that there are probably two black holes. One stands out a little bit, so you can see a clear signature. The other one looks like it’s covered in dust. So it’s very messy, quite complicated, but you know, very exciting. It looks like fireworks, but a bit messy.

KURTZLEBEN: I’m wondering if you could tell us what happened during this collision, kind of like a before, during and after game.

NATARAJAN: Right. So most likely this particular case is just one example, but it adds credence to our understanding that black holes also grow just by bumping into each other. So probably what happened is in a very dense environment, there were two galaxies, each with a central black hole that came very close and danced around a bit before crashing head-on. Once they collide head-on, these two black holes will likely become embedded in a kind of gas-dust disk, a cluttered disk. And they started kind of bumping into each other, kind of, you know, slowly spinning around 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, they shake all of space-time. So you have vibrations in space-time, gravitational waves that are generated when they eventually sort of merge together. At this moment we see the dance in advance. And then you have all those other fireworks. Like I said, you see the spectrum. You see all these signatures. So you see signposts before the final head-on collision. So we haven’t seen the final head-on crash yet, but it is inevitable. It’s going to happen, and we expect the final, you know, merger, as it’s called, to happen in the next few hundred million years.

KURTZLEBEN: Does all this mean that the crash has already happened and we’ll see it in the coming years, or is that still waiting to happen – it’s about to happen?

NATARAJAN: Yes. The crash has – in the context of black holes, the crash has already occurred.


NATARAJAN: It will 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. Which of your biggest questions does this answer?

NATARAJAN: The big open question is how they grow. So this observation actually supports the theoretical view that people like me have suspected for a long time that the growth of black holes takes place in two ways: a kind of accretion, that is, the absorption of gas. The technical term is gas accretion. gas, and by colliding with each other. And so we also expect that in the early universe, which was very dense, many objects were closer than they are today, making collisions more common. You know, it’s an indication that this image, this emerging image and the theoretical ideas that we had have been more or less validated.

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

NATARAJAN: So the new question, of course, is: How often do you do this? This is just one topic. That’s why we want to see how often mergers can occur. And like I said: right? – the final phase of this merger, of this crash, is that you end up with one big black hole, and you cause vibrations in space-time that we cannot yet detect. But you know, the European Space Agency and NASA are working together on a space mission called LISA that will actually measure the vibrations created in space-time, these gravitational waves. So I think this is kind of provocative, it opens the window and says, hey, these kinds of objects that are hopefully going to be ubiquitous that LISA is going to see.

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

NATARAJAN: I’m glad I got to talk to you about black holes.


KURTZLEBEN: Before we go, a sneak peek at 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 how many patients receive care. Some are opting for telehealth appointments to access abortion medications.

UNIDENTIFIED PERSON: I felt more comfortable in my situation than in a doctor’s office. And more comfortable, honestly.

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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