In A Flash Of Gamma-Rays A Star Is Gone
IRA FLATOW, host: This is SCIENCE FRIDAY, I'm Ira Flatow. Astronomers say they may be seeing the last dying gasps of a star as it is being gobbled up by a massive black hole. The evidence: mysterious, high-energy gamma-ray bursts first picked up in March. These high-energy bursts are not uncommon, but this one has lasted far longer than usual, tipping off astronomers that something big was happening about 3.8 billion light-years away.
The news was reported in two papers in the journal Science. That, along with another report about a slew of super-massive black holes previously hidden, existing in the very early universe, means it's time to get an update on all things black hole. And who better to do that than Lawrence Krauss, director of the Arizona State University Origins Project, his latest book, "Quantum Man: Richard Feynman's Life in Science." Welcome back to SCIENCE FRIDAY, Lawrence.
LAWRENCE KRAUSS: It's always good to be back, Ira.
FLATOW: Thanks for getting up early, and I know you're in Australia, so...
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KRAUSS: Yes, it's a good time. It's quite black here right now, so it's a good time to talk about black holes.
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FLATOW: Good. Also joining us is Joshua Bloom, associate professor of astronomy at the University of California at Berkeley and the lead author of one of those Science papers. Thanks for talking with us today, Joshua.
JOSHUA BLOOM: Happy to be here.
FLATOW: Lawrence, let me ask you first, let's just get grounded a bit and talk about what a black hole is.
KRAUSS: Well, simply, a black hole is something that's so massive, the gravity is so great that the escape velocity from its surface is larger than the speed of light, and since nothing can travel faster than light, nothing can escape, not even light.
So it's something that is completely separated from the rest of the universe, and we've never - it's - I should say that black holes are a theoretical construct. We see objects that we think are black holes, but we aren't 100 percent certain. They're just so massive and so dense that according to our theories, they can't be anything else.
I should say that they come in all different sizes, and one could imagine black holes ranging from the size of smaller than an atom up to billions of solar masses, and they have very different properties depending upon their mass, very different densities.
And we think they form - we're reasonably certain they form at least in one simple way, when some kinds of very massive stars collapse so that there are 10 to 100 solar mass objects that after they burn their nuclear fuel, there's nothing to hold them up, and they collapse down to become a black hole.
In fact, it was thought that it was originally impossible for that to happen, and John Wheeler, the physicist, originally argued that that shouldn't happen but eventually came around to realizing it must happen and coined the term black hole in the 1960s. And it's such a wonderful term that it's captured the public's imagination.
FLATOW: Joshua Bloom, tell us how you came to the conclusion that a giant black hole gobbled up a star.
BLOOM: Well, we arrived at that through a bunch of different observations that allow us to put this picture together. It was the energy. It was the time over which this event called Swift 1644+57, probably easiest just to call it the event because it's a bit of a mouthful.
The spectrum that we observed across the electromagnetic spectrum and in fact the location of this one event, near the center of a distant and quite anonymous galaxy, all of those pieces of evidence led us to believe that what we're seeing is indeed a black hole swallowing a wayward star as it happened to get too close to that black hole.
And the black hole beamed a jet of light and particles at us at Earth, which is why we saw these high-energy gamma rays. It's one of the sort of counterintuitive notions about black holes that I think it's worth bringing up that we think of them as these cosmic vacuum cleaners in many ways, sucking up everything around them, but actually, around black holes is where we get a tremendous amount of light in the universe.
It is an efficient place to change mass into light in an E=MC2 sense, and so when you have gas swirling around a black hole, that gas gets very, very hot, and before it falls in, it can be seen across the universe.
FLATOW: What would you have to do, then, to prove that this is what you're actually seeing?
BLOOM: Well, scientists like to stay away from the word prove just because there's always that little shred of doubt that is actually an important component of what we do. But what we can keep on doing is take more data and particularly take some data at radio wavelengths. So this is some of the longest radio light and light in the electromagnetic spectrum that we can observe.
And this object has been putting out copious radio photons, in addition to visible-light photons, and we may be able to see a jet emerge from this event over time. It will take a little while for us to be able to actually see it with even the sharpest radio eyes, but that may be one way to really solidify it for the community.
There are other possibilities out there of what this could be, but it's the combination of all the observations we have now that really are I think starting to make this picture a bit stronger.
One of the predictions of what it is that we're seeing, indeed if this is a black hole swallowing up a star, is that this event should never happen again. I think it's worth thinking about black holes and the life cycle of black holes not just in their sizes and their masses but in what they do to the surroundings.
Many black holes are sitting there essentially dormant. The black hole at the center of the Milky Way, for instance, is considered to be a dormant black hole that is not gobbling up lots of gas around it. It's not gobbling up nothing, but it's much less than many other black holes, about 10 percent of them, that have a tremendous amount of gas swirling around them, producing what are commonly called as active galactic nuclei or quasars.
And those black holes, we might think of their eating habits of ones of essentially voracious eaters with voracious appetites that last for millions or tens of millions of years. But the black hole that gave rise to this event that we're interested in was something more of a picky eater. It wasn't (unintelligible) lots of gas.
FLATOW: If you - it's hard for us to understand - I think that you're saying it would never happen again. That's an absolute you said that scientists never speak in.
BLOOM: Well, it's a prediction, and I should qualify never. I should say never in our lifetime or in mankind's lifetime, a prediction that this event should never happen from that galaxy again because the chances of a star getting too close to a black hole are actually pretty small.
We think, from theoretical understanding and actually from some other observational constraints, that this should only happen about once per super-massive black hole per million years. So that is, you'd have to look at a million galaxies in one year just to see one of these sorts of events.
Now this event was even stranger than that one in a million in that we had a very special vista on that event where the jet was pointing at us and not in some other random direction.
FLATOW: Let me get a - in the short time we have, Lawrence, what do you think? Do you think this is possible?
KRAUSS: Well, yeah, what's amazing about the universe is that it's big and old, and anything that isn't ruled out by the laws of physics happens all the time. As it was just pointed out, this is a rare event, so people may say, well, how can you believe a one-in-a-million event, but the point is there are 400 billion galaxies in the universe that we can see with telescopes, and therefore rare events happen all the time.
It may be rare in any one galaxy, but if we look at enough galaxies, we might see them, and we've discovered that the universe is stranger than we almost ever could have imagined. Anything that isn't ruled out happens. And as was pointed out, you might - what may surprise some of your listeners is everyone thinks of sort of black holes as cosmic vacuum cleaners, that if everything falls into one that's near one, but it's the not the case.
In fact, you can orbit around a black hole and not fall in, and black holes very effectively clear out the neighborhood around them, and after that, things that are moving far away from them don't fall in, and you have to be heading straight towards them to fall in. Otherwise you orbit around them just like you would the sun.
So these kinds of things are indeed rare, but it's amazing that every time we open a new window on the universe, such as the new window we're seeing here, we're surprised.
FLATOW: Well, in the minute or so I have left, another new window that was opened is a team of astronomers saying that they have found the oldest black holes yet, from the early beginning of our universe.
KRAUSS: Yeah. It's amazing because what we - what was just pointed is true that most galaxies nowadays, when we look at them, many of them have large black holes in their center, we think, including our Milky Way. We look towards the center of the Milky Way, we see stars orbiting around something that we can't see, and they're orbiting so fast that the only thing we can understand to explain is a million solar mass black hole at the center of our galaxy.
But what the astronomers have just seen using - looking for X-rays is the suggestion that even the earliest galaxies that were just forming in the universe may have had million or tens of million mass solar black holes, and that opens the question, the chicken-and-egg question: Were the black holes necessary for the galaxies to form, or were the galaxies necessary for the black holes to form, or were they necessary for each other to develop? And those are the kind of questions we're going to begin to answer as we look at the earlier, earlier universe.
FLATOW: One last question for you, Dr. Bloom. Where do you go from here?
BLOOM: Well, I think we need to understand whether we have actually seen an event like this from another galaxy in the past. There's great historical archives at high-energy wavelengths taken by many satellites over the last several decades. Now that we know what to look for, we need to ask that question have we actually seen this before but never recognized it.
And if we haven't, that gives us a pretty good handle on how often this sort of event happens. If we've seen it, then it allows us to start actually doing some sort of demographic studies of these. How were the other events different from this one? It allows to get, I think, a very nice picture of how black holes in this very interesting eating channel, swallowing up stars rather than gobbling up gas, how it is that they actually grow, how often does this event actually happen, and try to nail that down.
FLATOW: And Lawrence, what's the big question you'd like to know about black holes that are unanswered?
KRAUSS: Well, I'd really like to know if they're really black holes. As I say, everything we can see is indirect, and right now we say if it walks like a duck and talks like a duck or quacks like a duck, it's a duck. And these things look and act like black holes, but we haven't yet seen the really smoking gun that tells us that our theoretical understanding of gravity at its extreme limit is really true. And that would one day be wonderful. And we're not there yet.
FLATOW: All right, I want to thank both you gentlemen for taking time to be with us, especially you, Lawrence, out in Australia to get up or staying late or whatever you did.
KRAUSS: A pleasure.
FLATOW: Lawrence Krauss is director of the Arizona State University Origins Project. His latest book is "Quantum Man: Richard Feynman's Life in Science." Joshua Bloom, associate professor of astronomy, University of California at Berkeley and lead author of one of those science papers about black holes in this week's edition of Science. Thank you, gentlemen, have a good weekend.
BLOOM: Thank you very much.
FLATOW: Happy Father's Day to you. We've run out of time for this segment. We're going to take a break, and when we come back, we're going to switch gears and talk about using stem cells. Can and are stem cells being used to treat illnesses? And one special case, famous case, of a Yankees pitcher, New York Yankees pitcher Bartolo Colon, who went out of the country to get a treatment. But you'll learn that it's more common than you think it is. We'll have some details after this break. So stay with us.
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FLATOW: I'm Ira Flatow. This is SCIENCE FRIDAY, from NPR.
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