Planetary Radio: Space Exploration, Astronomy and Science - Gamma Ray Bursts: Explaining the Universe's Biggest Bangs

Episode Date: October 10, 2005

Swift satellite principal investigator Neil Gehrels on what causes the universe's biggest explosions. Q&A on the rings of Saturn, and a new space trivia contest during our What's Up segment about the night sky and more.Learn more about your ad choices. Visit megaphone.fm/adchoicesSee omnystudio.com/listener for privacy information.See omnystudio.com/listener for privacy information.

Big Bangs on the Edge of the Universe, this week on Planetary Radio. Hi everyone, welcome to Public Radio's travel show that takes you to the final frontier. I'm Matt Kaplan. Sometimes a story bursts upon us with such fury that we just can't ignore it. Such is the case with gamma-ray bursts, the biggest bangs since the Big Bang itself. And now we know what sets them off. Stay with us for a conversation with Neil Gerros, principal investigator for the Swift satellite.

Swift is watching for the next of these cosmic convulsions even as we speak. Bruce Betts is off hobnobbing with his fellow wizards. We'll get him on the phone for this week's What's Up visit, including the latest space trivia contest winner. Time for all the space news that fits. After 900,000 hours of work and over 120 modifications, NASA has turned Endeavor's lights back on. Crews cheered as the shuttle's electronic systems were powered up last week. It may still be over a year before the ship returns to space. And speaking of return to space, it appears that Hurricane Katrina may have delayed the next shuttle flight a bit more, from March of 2006 to possibly May.

The good news is that engineers think they have another fix for those foam-shedding external tanks. Thanks to listener Craig Journet for pointing us to these last two stories. Warning! Earth's oceans are dangerous to your health. Or at least they were a billion and a half years ago. NASA exobiologists have found evidence that sulfur compounds would have poisoned any advanced life, but those same compounds made a delicious primordial soup for some microbes. Still more from NASA. The space agency has named former astronaut Walt Cunningham as its latest ambassador of exploration.

He flew on Apollo 7's Earth orbiting mission, the first to send back live television pictures from space. Cunningham has handed his very own moon rock, which he promptly donated to the Frontiers of Flight Museum in Dallas. Our Lord, or rather Lady of the Rings, comes to us from Saturn this week. I'll be back with Neil Gerols right after Emily. Hi, I'm Emily Lakdawalla with questions and answers. A listener asked, how densely packed are Saturn's rings? Saturn's rings are often likened to the asteroid belt around the Sun, and both are made of

individual particles orbiting a large mass. But while the asteroid belt is so sparse that spacecraft can sail through it without worrying about hitting anything, Saturn's rings are quite dense. They are dense enough that collisions between particles are very common. The frequent collisions have broken any parent bodies into relatively small pieces. Particles in Saturn's main A and B rings are between the size of your fist and the size of a house. Near the edges of the main rings, the particle sizes shrink, the size of a bean or smaller. The frequent collisions also tend to average out the orbital motions of the particles,

bringing their orbits down into an exceedingly flat plane exactly aligned with Saturn's equator. If you were sitting on a ring particle in Saturn's A or C rings, you would see particles everywhere around you, keeping pace with you, but you could look straight through the ring plane to see black space beyond. What you'd see in Saturn's densest B ring

would be quite different. Stay tuned to Planetary Radio for more. Neil Gerol's watch is for events that may have happened before life formed on Earth, and in some cases, before there was an Earth. The principal investigator for the Swift satellite was a key presenter in a NASA press conference last week. He announced amazing discoveries regarding gamma-ray bursts. These explosions released the equivalent of a star's lifetime energy output in mere seconds.

No wonder they can be seen from billions of light-years away. And as we learned from Neil, there's good reason not to get a whole lot closer. We spoke immediately after he had returned from Germany to the Goddard Space Flight Center in Maryland. Neil, that was quite an explosive announcement that you and your team got to make last week. Oh, yeah, indeed. We're tremendously excited by this new discovery that the Swift satellite has made. tremendously excited by this new discovery that the Swift satellite has made.

This recent one has been in conjunction also with another NASA satellite called the HETI mission, and also with over 20 different ground-based observatories and observations. Quite a bit of coordinated astronomy here. What is it about Swift that makes it uniquely qualified to find and train instruments to observe these events that happen very, very quickly. Swift is designed specifically to study gamma-ray bursts. They're very brief flashes of gamma rays. They occur about once a day in random places across the sky, and they typically last some tens of seconds. And the SWIFT satellite was specifically designed to study these bursts.

It has a gamma-ray detector on it, some detectors that whenever a gamma-ray hits them, they make a little electronic pulse, and we can tell. We can actually count the number of gamma-rays that are hitting it. can tell. We can actually count the number of gamma rays that are hitting it. And that instrument determines the position of the burst roughly on the sky. The real new innovation of SWIFT, which is actually where we got the name, is that when that position's been determined, the satellite computer reorients the whole spacecraft, the whole satellite, to point two other instruments at the position of the burst. And that's an X-ray telescope and an optical telescope. So very smart spacecraft, and it does all this autonomously.

It does it autonomously, and it does it rapidly. That's where Swift comes from. I also read that Swift puts out the word to the astronomy community on Earth. I mean, did you get like an instant message or a cell phone call from your spacecraft? Not only myself, the whole SWIFT team gets this message. We also put that message out on the Internet for observers all around the world to train their telescopes at the burst. Now, for our team, it isn't so much to go look with another telescope, but we want to get on the computer and look and see what we've got right away. So it actually pages our cell phones about a third of the time. You know, they go off in the middle of the night.

Of course. And so we're often getting awakened. And of course, it's fun to rush down and see what's just happened. And because SWIFT alerts the astronomy community, that's, I assume, how these land-based instruments are also able to turn their big lenses toward this event in the sky. That's exactly right. There are some specialty telescopes that all by themselves just take that signal coming on the Internet and repoint themselves. And then there are bigger telescopes like the Keck Telescope in Hawaii and the very large telescope in Chile that get repointed by an observer. But they can do it quite rapidly within a matter of minutes to an hour. And this quick response was key to the discovery, to the announcement that was just made.

That's right. SWIFT makes a lot of observations on board, you know, the data that we get from our three instruments. That was very important for understanding these new short bursts. But we learned even a lot more from the ground-based observations. birth, but we learned even a lot more from the ground-based observations. Well, what you discovered, apparently, is that these births are quite cataclysmic events taking place, at least so far, the ones that have been found so far, a long, long ways away from our solar system. That's right.

There are actually two different discoveries we've made. They've both been announced within the last two or three weeks. One thing, actually the first thing that we announced was a big surprise. Most of these bursts occur far away in the universe. That was known even before Swift. They can be billions of light years away. It's awesome how much energy gets produced in the explosions that make these gamma ray bursts since they're so far away. But on September the 4th, we detected a burst that looked different than other ones.

It had a longer time profile, was very faint and hard to detect. And by the time we were done understanding it over the next three days, we realized that it was one of the most distant objects that had ever been seen in the universe. How far? How many light years? So it was 12.8 billion light years away. Wow. And so as our audience, our sophisticated audience, of course, knows, you were looking at an event that took place that far back in the past as well. That's right. It's like a time machine. Those gamma-ray photons, those particles of gamma-rays,

you know, it's light, but think of them as photon particles, have been traveling toward us for 12.8 billion years. They were produced very early times in the universe. The universe was only 800 million years old at that time. You know, that sounds like a big number, but it was such a small fraction of the time since from now to the Big Bang. So it was very early. We're probably going to have to take a break before we can talk about what you've actually discovered about the origin of these gamma ray bursts. A question that I've been dying to ask, what would happen if one of these took place in our neighborhood,

let's say within, oh, 10, 20 light years? These are so powerful. If there were one that nearby, it would essentially wipe the atmosphere right off the earth. Wow. The probability of that happening is very small, infinitesimal. But the probability of there being one within our own galaxy, let's say, you know, some thousands of light years away,

that gets to be a little larger. There probably has been one during the last few hundred million years when there was life on Earth that was near enough that it disrupted the ozone in some way and may have had an effect on life. Even from a distance of, let's say, hundreds of light years, or perhaps thousands? At ten light years, you would wipe the atmosphere out. At thousands, you would disrupt the ozone, you know, have a significant reduction in

the ozone for a period of a year or two, which would, you know, that would affect life. And when you get into the range in between, it kind of varies. Well, let's come back in a minute and talk about what you have found, what we can now state with confidence is actually happening when these, calling them large explosions, there's no way to state how big these are without making an understatement, I think. But when we come back from this quick break, we'll pick up our conversation with Dr. Neil Gerrels, the principal investigator for the Swift satellite,

who now has a pretty good idea of what is causing these gamma-ray bursts far away in our universe. We'll be right back. This is Buzz Aldrin. When I walked on the moon, I knew it was just the beginning of humankind's great adventure in the solar system. That's why I'm a member of the Planetary

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The Planetary Report. it's just one of our many member benefits want to learn more call us at 1-877 planets that's toll free 1-877-752-6387 the planetary society exploring new worlds welcome back to planetary radio where our guest is Dr. Neil Gerrels, the principal investigator for the Swift satellite. He works out of the Goddard Space Flight Center, NASA's Goddard Center, of course, in Greenbelt, Maryland. Neil, we were just talking about, I said, I don't know how we would even express how big these explosions are, but I guess you want to take a stab at it.

How can you put these into terms that we might appreciate just how big a boom these are? There's a couple of different ways to think about it. First of all, they are the most powerful explosions in the universe since the Big Bang. So this is the top banana. And there's as much radiation, there's as much energy that comes at us in this few-second pulse of gamma rays as the sun puts out at all wavelengths over its whole lifetime. Wow. So that's one way to look at it.

And another way is if you took a star like the sun and you could turn all of its mass into E equals mc squared energy, could turn all of its mass into E equals mc squared energy. That would be a little bit more than the energy of a gamma-ray burst, but it gives you about the right scale. That is, you know, even at that, it is beyond belief. What have you discovered could cause such a cataclysm? Most of them are in this long-burst category, and then later we'll talk about the short birth, each of which have, we believe now, have completely different origins and causes.

The longer birth, this very distant birth from September the 4th was in this long birth category. We believe now are caused by the collapse of massive stars. Take a star that's, say, 40 times as massive as our sun. When it reaches the end of its life, it burns out its nuclear fuel in the middle, and then gravity wins out. These big, massive stars collapse. Even before gamma-ray burst studies, people knew about stars ending their life in explosion, called supernovae. But we think with the gamma-ray bursts, the core of the star collapses to a black hole. And then all of this gas falling in on the black hole produces a huge amount of energy. And we believe that's what causes the gamma-ray bursts.

The longer variety, which I take it, are the ones that last roughly more than two seconds. Right. That's the dividing time, about two seconds. A typical long burst will last maybe 20 seconds or so. That's still very fleeting. Yeah. What about the others, the less than two seconds, which are what, about 30% of these bursts? Yeah, about 30%. We've just, for the very first time, gotten, I'd say, the beginnings of understanding of what causes the short bursts. We were able to image the first short burst just in May of this year,

and now there have been three or four of them that both SWIFT and, I mentioned, this HETI satellite have imaged. All of these bursts you see come from galaxies, All of these bursts you see come from galaxies, and we can see where in the galaxy and what type of galaxy they are to try to determine what kind of stars are making the explosion. So you've discovered that these shorter bursts are not caused the large bursts, but right up there with supernovae and huge explosions. The short bursts are coming from galaxies that don't have massive stars in them. That was our first hint that they're coming from a binary pair of stars, not just any kind of stars, but old, condensed. We think of them as neutron stars as one type that is a good prospect.

And as they orbit each other in this binary system, they lose energy from their orbit by gravitational waves that come out slowly. Over a period of billions of years, the orbit gets closer and closer. And then the final part goes in seconds, where the actual hard stars collide with each other. It's a big explosion. We think that's what makes the short burst.

So that's a neutron star. And a neutron star, and I read that some of these may be a neutron star colliding with a black hole. Yes. We know so little about how many black holes there are in the universe versus how many neutron stars there are. You can't predict ahead of time. There may be different signatures for a black hole neutron star binary or a neutron star neutron star binary.

I think it will take some more time to sort that out, but we have some preliminary evidence that one of these short bursts was a black hole neutron star merger. There is, in fact, on your website, the SWIFT website, and we will put up a link to that site at our website, planetary.org, There is an animation of exactly this kind of event taking place, and it is cosmically terrifying to watch. I know. Isn't that an awesome animation? It really is. And we think that's really what it looks like.

We did the best we could, you know, consulting the brightest minds to try to make that animation look realistic. And basically what you see in that animation is, as the last few orbits of these stars, they're tearing each other apart. And the amazing thing is that when all is said and done, these two stars have collapsed down into a black hole. The Gamma Rebirth is like the birth cry of a black hole that's just been born. So it's not just the black hole that was part of the collision getting bigger, if you will.

It's really considered a new black hole. Right. In the case of the two neutron stars orbiting each other, it's a new black hole that was born. Yeah. If it's a black hole neutron star system, then it still ends up being a bigger black hole. Where does your research go from here? You stay on the lookout for these, I bet. Yes.

Swift will be in orbit for 10 years, and we detect about 100 births a year. Each one is different. I'm guessing that we'll find births of other types that we haven't even thought about. This is a fairly young field yet. Well, we will hope that most of those phone calls from Swift come to you at better times than when you're fast asleep. But it is very exciting stuff. If these collisions resulting in these births were more common in the early history of the universe,

and if they are so damaging to planets that are fairly nearby, I would guess that these bursts may have played a pretty important role in the chance that life developed, at least early on, elsewhere in the universe. They could indeed have done that. There has been quite a bit of discussion and debate about that. in the chance that life developed, at least early on, elsewhere in the universe. They could indeed have done that. There has been quite a bit of discussion and debate about that. But exactly as you say, they may have been more common in the early universe. They serve as a kind of sterilizing factor for the region of the galaxies that they're in. any planets in that area would have, if there

were life on them, they would have that disrupted. It certainly would have an effect on their atmosphere. Well, then we will hope that you continue to get these bursts to study, but that we don't get one too close to home. And I wish you great luck as you continue these observations. Okay. Thank you, Matt. It's been a pleasure talking with you.

Thank you very much, Neil. Neil Gerrels has been our guest. He is a principal investigator for the Swift satellite, working from the Goddard Space Flight Center, one of the main NASA centers, of course. He has been talking to us about gamma-ray bursts, about which we have apparently learned more in just the last few years than was known in all of human history. We'll be back with a bit more history for you, a bit more recent history,

as part of What's Up, our weekly visit with Bruce Betts, right after this. I'm Emily Lakdawalla, back with Q&A. What would the view from a particle in Saturn's B-ring be like? First of all, if you tried to look through the densest part of the B-ring to the other side, you wouldn't be able to see it. The middle of the B-ring is so densely packed that it is optically thick, meaning that light and radio waves cannot pass through it to the other side. If you tried to look down through the ring, your view would be blocked by infinite numbers of particles.

An astronaut could scramble from one particle to the next with ease. If light can't get through from one side of the ring to the other, then individual particles can't make the passage either. Any B-ring particle on a path that attempted to cross the ring plane would be stymied by the other particles in its way. That means that B-ring particles always stay on either the sunlit side or the shadowed side of Saturn's ring plane. One side of the B-ring is sunlit and hot for half of Saturn's year,

while the other side is shadowed and cold. In this way, the B-ring actually behaves almost as though it were a solid disk orbiting Saturn. Got a question about the universe? Send it to us at planetaryradio at planetary.org. And now here's Matt with more Planetary Radio. Time for What's Up on Planetary Radio. We are joined by Bruce Betts, the Director of Projects for the Planetary Society, who for the first time in ages is not able to talk to us face-to-face.

We're just ear-to-ear today. I have you on the phone. Bruce, where are you? I am in Arlington, Virginia. I am attending the Outer Planets Assessment Group meeting. You're assessing those outer planets, eh? Yes, I am. Well, I hope they all pass, and I hope that you can tell us a little bit more about that a little bit later. Me too.

You're tired, aren't you? But in the meantime, I am. In the meantime. What's up? What's up in the night sky? We've got, of course, Mars just looming large and beautiful and rising around 9. Look in the east. And then by midnight, it's up high in the sky.

Can't miss it these days. Very bright. Looks like a very bright orangish star. And that would be Mars. You can also check out Venus in the evening sky low in the west after sunset, looking like a very bright whitish star. And then in the pre-dawn sky, you can catch Saturn in the east, looking like a not-so-bright white star.

And for those of you hanging out in areas in or bordering the Pacific, look for a partial lunar eclipse on October 17th. On to this week in space history. This is the 25th anniversary, the 25th birthday of the Very Large Array in New Mexico, a set of 27 radio telescopes that are used to study the universe. That starred with Jodie Foster in the movie Contact. They did a fair amount of the filming there, I think.

Yeah, it took a while to train the antennas to act. Well, they could say that about many of us. They can listen great, but they didn't hit their lines very well. Okay, on to human space update. We've got five people up on the International Space Station as we record this. Expedition 11, Sergei Krikalev and John Phillips will be headed home on Monday, October 10th, along with spaceflight participant Gregory Olson, a private citizen, who's up there for a few

days. And meanwhile, William MacArthur and Valery Tokarev will take over as Expedition 12, and we'll be up there for about six months. On to Random Space Fact! Just can't help but go to those outer planets. Pluto. I got the spiffy fact off of the New Horizons mission website. New Horizons, a Pluto mission, launching January 11th, they hope, our first visit to Pluto, at about 1,500 miles in diameter. That's about 2,400 kilometers across.

Pluto would fit between where I am, approximately Washington, D.C., and Denver, Colorado. Oh, I love those. I love those little common terms of measurement things, you know, measuring things in football fields or bread boxes, you know. Well, it would be a lot more bread boxes. Yeah. On to the trivia contest. We asked you last time around, we asked you what was the first Japanese Earth-orbiting satellite.

What was the name of the first Japanese Earth-orbiting satellite? How did we do, Matt? There are a whole bunch of people out there who apparently want a Planetary Radio t-shirt, and so we're seeing more entries just about every week. One of them came from Joel Tatham. Joel Tatham of, get this, Grundersburg, Suffolk in the United Kingdom. Joel says Japan's first satellite was the Osumi, launched on February 11, 1970. It reentered the atmosphere in 2003, and he said he was surprised to read about the scarcity of instruments,

but that it was probably just a glorified payload. There you go. I think he got it right. He sure did. And for this next time around, you too can win a Planetary Radio t-shirt by answering this question back to the VLA. What is the diameter of each of the 27 radio telescopes that make up the very large array? To answer this question, get into the trivia contest. Go to planetary.org slash radio.

Follow the directions there. And, hey, could you do us a favor and tell us where you hear us? Because we're getting out there so many places, we want to know. Thank you very much. So, you want to hear about outer planets? Well, before we do, I'll tell them that they want to get their entry into us by the 17th, October 17, Monday at 2 p.m. Pacific time. And, yeah, please take a minute or so. I know you're tired there after a hard day of conference going, but tell us what's going on.

Well, we heard updates today on the two selected outer planets missions, as well as the one that's out there right now, Cassini, of course, orbiting Saturn, New Horizons launching in January off to Pluto-Sharon, and then hopefully on to Kuiper Belt objects, and the Juno mission recently selected, which will be a Jupiter polar orbiter to launch towards the end of this decade, all of them proceeding nicely. And then there were discussions of exotic farther future things,

like missions back to Titan around Saturn and missions to Europa. And, in fact, the Planetary Society is getting geared up to work on various aspects of trying to advocate for and facilitate a Europa mission to Jupiter's moon that may have a subsurface ocean. Excellent. Good for us. Sounds like fun. A lot going on in the solar system. There sure is. Very interesting. I think we're done. Say goodnight, Bruce. All right, everybody. Go out there, look up at the night sky, and think about obelisks. I know I am. Thank you, and goodnight.

He's Bruce Betts. He's the Director of Projects for the Planetary Society, and he joins us each week this time from Arlington, Virginia, for What's Up. Back next time with more true adventures from our best of all universes, and be sure to join us in two weeks when author Ray Bradbury returns to Planetary Radio just before he receives the Thomas P pain memorial award for advancement of human exploration of mars our show is produced by the planetary society in pasadena california you can reach us at planetary radio at planetary.org say it fast three times planetary planetary planetary have a great week everyone everyone.