New images show a black hole collision

DANIELLE KURTZLEBEN, HOST:

The James Webb Space Telescope amazes us again with a new discovery that redefines our understanding of the origins of the galaxy. New images show the collision of two giant black holes and it is the most distant black hole merger ever observed. The collision occurred just 740 million years after the Big Bang that formed the universe. And we’re talking about it with someone who lives and breathes in black holes. Priyamvada Natarajan is an astrophysicist and head of the astronomy department at Yale University. Priya, welcome.

PRIYAMVADA NATARAJAN: Thank you very much. I’m excited to talk to you about black holes.

KURTZLEBEN: Well, great, because we’re starting with the absolute basics. So remind us what a black hole is and why it matters that we discovered a merger between two of them?

NATARAJAN: So a black hole is – you can think of it in different ways, but one important – simple way to think of it is a special place in space where a lot of matter is concentrated. And it’s so concentrated that it somehow distorts the shape of the space-time fabric in which it sits. So we’re all embedded in spacetime – right? – The entire universe is embedded in this four-dimensional sheet, and every matter creates a small dent in this kind of fabric, which is actually four-dimensional, but we can just think of it as fabric. But what a black hole actually does is puncture spacetime. So it’s a very dramatic change in the shape of the room. And that’s because 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 there are black holes virtually everywhere, and there is one at the center of our own galaxy that is 4 million times the mass of the Sun. So the big questions are: Where do they come from? How did they come about? And James Webb opens up the early universe. We have these new eyes in the early universe, and we see that in galaxies – very, very early galaxies – supermassive black holes were already lurking in the centers of those galaxies when the universe was barely several hundred million years old. And we don’t know how these black holes actually form and how they grow. It is therefore assumed that mergers represent an opportunity for their growth. The other just guzzles gas.

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

NATARAJAN: A million times the mass of our sun…

KURTZLEBEN: Oh.

NATARAJAN: …We often refer to this.

KURTZLEBEN: Yes. Maybe describe to us what this collision looks like in these pictures.

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

So the spectrum consists of the energy given off by the stars and the growing black hole that James Webb captures. And in this spectrum there are very clear signatures that indicate that there are probably two black holes. One of them pops, so to speak, so that you can see a clear signature. The other looks like it’s covered in dust. So it’s very messy, kind of complicated, but, you know, very exciting. It’s like fireworks, but kind of chaotic.

KURTZLEBEN: I’m wondering if you can tell us what happened during this collision, bit by bit before, during and after, so to speak.

NATARAJAN: Right. So this is most likely just one case, but it strengthens our understanding that black holes also grow by simply crashing into each other. So what probably happened in a very dense environment was that there were two galaxies, each hosting a central black hole that came very close and danced around a bit before colliding head-on. Once they collide head-on, these two black holes would likely be embedded in some kind of gas dust disk, a messy disk. And they started hitting each other, dancing slowly in circles, getting closer and closer.

And eventually they would completely collapse and crash into each other. And when they do, they shake all of spacetime. So there are tremors in spacetime, gravitational waves that arise when they eventually merge together. For now we’re previewing the dance. And then there are 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 collision. So we haven’t seen the final head-on collision yet, but it is inevitable. It’s going to happen, and we expect the final merger, as it’s called, to happen in the next few hundred million years.

KURTZLEBEN: Does all of this mean that the crash has already happened and we will only experience it in the next few years, or does it still have to come – it is coming?

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

KURTZLEBEN: Yes.

NATARAJAN: It’s going to take some time before we actually see it – right? – because of the speed of light and the distance.

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

NATARAJAN: The big open question is how they grow. So this observation, in a way, supports the theoretical picture that people like me have long suspected, that the growth of black holes occurs in two ways, namely through a kind of accretion, that is, through the devouring of gas, the technical term for this is accretion gas and through collisions. And so we also assume that in the early universe, which was dense, many objects were closer than they are today, so collisions occurred more often. You know, it’s an indication that, hey, this picture, this emerging picture and the theoretical ideas that we had are kind of confirmed.

KURTZLEBEN: Now that you have this new information, what will you look at next? What are your new questions?

NATARAJAN: The new question, of course, is how often does this happen – that’s just one goal. So we want to see how frequently mergers can happen. And as I mentioned – right? – The final phase of this merger, this crash, is that at the end a large black hole is created and tremors are created in space-time that we do not yet have the necessary equipment to detect. But, you know, the European Space Agency and NASA are collaborating on a space mission called LISA, which will actually measure the tremors that arise in spacetime, these gravitational waves. I find it kind of tempting to open the window and say, “Hey, these are objects that LISA will hopefully see ubiquitously.”

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

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

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KURTZLEBEN: Before we go, a preview of a story coming up tomorrow on All Things Considered. Nearly two years after the Supreme Court ruled on Roe v. Wade repealed, a lot has changed when it comes to abortion access, including how many patients are treated. Some are choosing telemedicine appointments to access abortion medications.

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

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

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