Fire in the Sky
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PHIL PONCE: Astronomers have found evidence of what may have been the most powerful explosion since the universe was created in the so-called “Big Bang.” In fact, the light from this explosion is believed to have been so strong that for a few seconds it was brighter than all the stars in the universe put together.
Here with more on the discovery is David Helfand, Professor of Astronomy at Columbia University. Welcome, Professor Helfand. First of all, what kind of an explosion are we talking about? What blew up?
DAVID HELFAND, Columbia University: Well, for the past 30 years since we first detected one of these intense flashes of high energy radiation from a random spot in the universe we’ve wanted to know the answer to that question. And while I certainly can’t say today we know the answer, at least we’ve taken one big step towards it in that at least we now know where the flash came from.
PHIL PONCE: And before we get to where the flash came from, just how big of a flash was it? How much energy was involved?
DAVID HELFAND: Well, it’s hard to compare to human scale terms. The most energetic explosion we’ve known of in astronomy prior to this is the collapse of a massive star at the end of its life that we call a supernova. For the 10 seconds this was shining in gamma rays it was about 5 billion times as bright as the supernova.
PHIL PONCE: And how do you know it happened? What evidence do you have?
DAVID HELFAND: Well, on December 14th , a little before midnight, Rome time, an Italian satellite, which has been designed to detect these sources, recorded a flash in their cameras of gamma rays from a random spot in the sky. The great advantage of this camera over all previous ones is that it’s able to localize the direction from which the flash came, in this case with an area of maybe 5 percent the size of the full moon.
PHIL PONCE: Now, we have some pictures that were provided to us of–for want of a better term we’re calling an “afterglow.” The first picture that we have is–was taken a day after the event was first–the night after the event was first observed. And, the second one we see where the afterglow is fading even in relative proximity to when it was first observed. What do these images tell us, Professor?
DAVID HELFAND: Well, what happened was that around midnight, New York time, I got a call from the group in Rome who said we have a burst, we need a telescope. So I called our MDM Observatory in Arizona, where one of my colleagues, John Thorstenson, was on the telescope with a camera that could take a picture of just this piece of the sky.
The first image you saw was the night of the burst, itself, about eight or ten hours after the explosion. And the second was taken the next night. You see, all the other stars and galaxies in that image are unchanged because most things change very slowly in astronomy. Stars live for billions of years. But that one you have a circle around faded by a factor of five from one night to the next. And that’s when we knew we had pinpointed the location of the burst.
PHIL PONCE: And further evidence of where this burst came from was provided through the Hubble Telescope. We have some images from that. And tell us what we’re looking at, these color images here.
DAVID HELFAND: Well, that little spot in the center there now is no longer the burst, because this is taken four months later, and it’s faded away. But what it shows is the host galaxy, the location where the burst took place, which turns out with the Keck observations that our colleagues at Cal-Tech made, to be located more than 3/4 of the way across the universe.
PHIL PONCE: Taking these images together, what can you conclude?
DAVID HELFAND: Well, the first and most important inference we can make–since we now know the distance of about 12 billion light years–we can calculate how much energy must have been involved in the burst at the source. And that’s what comes out to this enormous number much greater than anything we’ve seen exploding before.
PHIL PONCE: And you just mentioned 12 billion light years, so it took place 12 billion years ago, and how long ago is the universe believed to have been created?
DAVID HELFAND: This is about 85 percent of the way back to the beginning of time. The burst, indeed, took place about 8 billion years before the Earth even formed, and it’s been traveling to us through space all that time, just arriving on December 14th.
PHIL PONCE: So basically, we are getting images of something that happened a long time ago, and explain–explain how that works, that something that happened billions of years ago, the evidence of it just–just is now arriving, so to speak.
DAVID HELFAND: That’s right. Whenever we look out into space, we’re effectively looking back into time because light travels at a finite speed, albeit very fast, something like 6 trillion miles a year, but that’s a short distance in the space of the universe. As a consequence, whenever we look at a star or a galaxy, we’re looking at the light and the star and the galaxy as it was many years, millions of years, or even billions of years, as in this case, ago, when it left that object. And it’s been traveling to us ever since.
PHIL PONCE: So it’s kind of a visual echo?
DAVID HELFAND: In some sense.
PHIL PONCE: Does this explosion have anything to do with the Big Bang, or is there any connection between it and the Big Bang?
DAVID HELFAND: Well, the Big Bang really is not an explosion in the normal sense. An explosion takes place at some point and place, at some moment in time. The Big Bang created time and space itself. So it really is a more universal event. But this occurs 85 percent of the way back in time to when the Big Bang occurred.
PHIL PONCE: And Professor, the $64,000 question: What caused it?
DAVID HELFAND: What caused it? Yes, well, as I said, we’ve been waiting for 30 years to answer that question. And we’ve only taken the very first step along the road to the answer. There are about 150 separate theories that have been published for the origin of gamma ray bursts over the last 30 years. This destroys about 146 of them or so. But there are a few that are still viable.
PHIL PONCE: In fact, we have some animation, which illustrates one of the theories. What theory does this particular animation suggest?
DAVID HELFAND: This suggests the little white thing, which is a neutron star, is falling into a black hole. A neutron star is the densest form of matter we know, a billion tons per teaspoonful, an entire star compressed into something smaller than Manhattan.
If it’s eaten by an even larger black hole, an enormous amount of energy will be released in the last few seconds as it spirals in. And this animation is meant to illustrate what could possibly produce the burst from that event.
PHIL PONCE: Do you have–do you personally have a particular theory that you’re subscribing to?
DAVID HELFAND: I try to stick to the observations and let the theorists remain with their speculation.
PHIL PONCE: Professor, if this was such a big explosion, why is that it’s just discovered now?
DAVID HELFAND: Well, we see one of these bursts arriving from a random direction almost once a day. So there are lots of these going on in the universe. The thing is that till now we’ve never known how far away they are, and, therefore, didn’t realize how enormously energetic they were.
PHIL PONCE: Based on the sequence of events that led to the observation, it strikes one that some luck was involved in observing this. Was this a lucky find?
DAVID HELFAND: Yes. I think this is a good example of the role serendipity plays in scientific discovery. If I hadn’t been in my office on a Sunday evening at 11 o’clock, which is probably the only time in 20 years I’ve been there, I wouldn’t have received a phone call, and we might have missed the opportunity to pinpoint the location of this burst.
PHIL PONCE: Because you got the phone call, you were able to alert people to take pictures of it?
DAVID HELFAND: That’s correct.
PHIL PONCE: Well, it sounds like it was sort of in the stars for this to happen to you. What has been the reaction in the scientific community to this?
DAVID HELFAND: Well, most of my colleagues who have been generating these models for how these bursts might occur are nonplussed, I think, is the best way we can say it. They see most of their theories evaporating and are scrambling to find others.
The reason this is exciting, I think, beyond just the solving of this old mystery, is that it probably will provide us an opportunity to test the laws about the interaction of matter and energy and space and time that we derive in our earth-bound laboratories in a situation that’s much more extreme and, therefore, pushes these laws to their limits. If they pass the test, we have much greater confidence in our understanding of the physical universe. If they fail, it provides an opportunity for us to explore and expand our understanding of space, time, matter, and energy.
PHIL PONCE: And how about for the layperson, aside from it might mean within the scientific community, what does this mean to a layperson?
DAVID HELFAND: I think everyone loves a mystery, and so the fact that we’ve taken the first step towards a solution but don’t yet even have a viable model is a story that’s worth telling. But, again, I think it’s the role that astronomy has played over the last several centuries of allowing us to expand the bounds of our knowledge beyond our laboratories on earth to a much grander scale and, therefore, understand things in a much deeper perspective.
PHIL PONCE: Professor Helfand, thank you very much.
DAVID HELFAND: You’re welcome.