GWEN IFILL: Finally tonight, they’re big, they’re scary, and, lucky for us, they’re about 300 million light years away.
We’re talking about the largest black holes in the universe, and nothing, not even light, can escape their gravitational pull. Astronomers recently discovered two black holes, each one 10 billion times the size of our sun. Their findings are being reported this week in the journal “Nature.”
Joining me now is Chung-Pei Ma. She is a professor of astronomy at the University of California, Berkeley, and led the team that published the study.
Welcome to the program.
Describe for us how massive, really, these holes are that we’re talking about.
CHUNG-PEI MA, Professor of Astronomy, University of California, Berkeley: Yes.
Each one has the mass of about 10 billion times that of the sun. And we can also think about their sizes, that is to say, the region of space within which light cannot even escape. And that size for these black holes are about five times that of our solar system, so within which these objects are dark.
GWEN IFILL: What are black holes really, and how does one go about finding them?
CHUNG-PEI MA: Right.
So, black holes are these regions of space where the gravity is just enormous. And so, by that definition, they are dark. So, we have to use things we can obviously see. So, in this case, we used stars that are orbiting very close to the black holes. And we measure their speeds.
And the faster the stars are moving, that indicates they’re feeling stronger gravity, and, therefore, the more massive the black hole would be.
GWEN IFILL: Now, you didn’t obviously see these with the naked eye. How did you find them? How did you even know where to look?
CHUNG-PEI MA: Yes, they are hard to find.
They are hiding at the centers of very massive galaxies. So, in order to measure these stars, we relied on state-of-the-art telescopes, such as the Gemini and the Keck telescopes in Hawaii and the McDonald Observatory in Texas. And we used the spectrographs on them, very sensitive ones, to measure the orbits of these stars.
GWEN IFILL: We — you have found black holes — in fact, your team has found them before. Why are these so big, so huge? What is it about the ones you found that’s different from what you have seen before?
CHUNG-PEI MA: Yes.
The previous record-holder had a mass of about half of the ones we saw. And they were done by our — two of our team members, Karl Gebhardt in Texas and Tod Lauer at NOAO. And these two we found, however, dwarfed them by a factor of two.
GWEN IFILL: Now, you describe them as — absence of light is what a black hole is by definition. So, how do you know that what you’re looking at when you find it is actually a black hole, and not just space?
CHUNG-PEI MA: Yes.
So, what we’re able to do is, we are able to estimate the amount of mass that is enclosed within the orbit of these stars. And since there’s an enormous amount of mass concentrated at a very small region in space, we believe the best candidate for the thing that is pulling on the stars would be a black hole.
GWEN IFILL: So, we know that they’re — we have an idea — I don’t know if we can actually — we can see, though, how big they are, but how far away are they from us? Is this something that seems closer than what you have seen before, or is it farther away?
CHUNG-PEI MA: Yes.
So, the previous record-holder was in a galaxy that’s much, much closer to ours, about a factor of 20 closer. And these ones we saw are at — in a galaxy that’s about 300 million light years away. And that sounds like a very large distance, but for galaxies — we know about many, many galaxies — these are actually quite nearby.
GWEN IFILL: Nearby, but not a threat? I mean, we’re not — you’re talking about black holes that suck in light and gases and everything in its path, but we’re not in its path?
CHUNG-PEI MA: That’s right.
So, what made this observation very difficult is, like you said, we are observing the stars near the black holes. But we needed to look at stars very close to the black holes. So, in this case, we’re looking at stars within about 1,000 light years of the black holes. That sounds like a large distance, but that region is at 300 million light years away, so it required very sharp eyes.
That is, you need to have very good glasses to — in order to see these stars.
In our case, we relied on the state-of-the-art telescopes.
GWEN IFILL: So, tell us about what — why these black holes matter to us? Are they — does that say something about the galaxies that we know of, that we live in? Does it say something about the universe?
CHUNG-PEI MA: Yes, absolutely.
Astronomers have known for some time that bigger galaxies seem to have bigger black holes. That is to say, the black holes seem to know about the big environment that they live in. They live at the centers of these galaxies.
And this correlation is very important, because it indicates that, when we learn about these black holes, when we do these measurements, that can also help us understand how their parent black holes were assembled. And galaxies are, after all, the building blocks of the universe. And this will allow us to understand how the universe evolved.
GWEN IFILL: Well, thank you for allowing us to understand the building block, Professor Chung-Pei Ma of Berkeley.
CHUNG-PEI MA: Thank you.