Follow this link to skip to                                      the main content

Web Broadcasts

Text Size

Launch Services Webcast: Science and Spacecraft Overview
Questions and Answers with Dr. Neil Gehrels

Rex Englehardt: Thanks, John. Joining us now in the studio is Swift's Principal Investigator, Neil Gehrels. Neil works at NASA's Goddard Space Flight Center and is the lead scientist for the project. Neil, how did you get involved in Swift?

Dr. Neil Gehrels: I've been working in astrophysics for about 20 years and gamma-ray bursts have fascinated me since I first learned about them when I was in graduate school. When we learned that they were occurring in galaxies outside of our universe, it motivated us to design this satellite to study gamma-ray bursts.

Englehardt: Well thank you, Neil. We do appreciate you spending some time to answer some questions from our viewers.

Gehrels: My pleasure.

Englehardt: By the way, one lucky question board participant will be winning a mission gift pack today. I'll announce the winner at the end of the show. Neil, let's get started.

Gehrels: I'm ready.

Englehardt: Alright. Our first question comes from Josiah from Ellingsworth. What is the satellite going to do?

Gehrels: Well, Swift was designed to solve the mystery of gamma-ray bursts. As Rex said earlier on the show, we've known about gamma-ray bursts for 40 years, but we still don't understand what causes them and Swift was designed with all the capabilities to solve this mystery.

Englehardt: That's interesting. Our next question comes from Mary Lou from Iowa: What are gamma-ray bursts?

Gehrels: Well, that's a straight-forward question. Gamma-ray bursts are short and very bright flashes of gamma rays that occur all across the sky. They last for just a few seconds, and we now know that they are occurring in distant galaxies and are very powerful explosions.

Englehardt: Wow. The next question we have comes from Junichi from Japan. How large an amount of energy does gamma-ray bursts spread in an instant? Please explain it in concrete for me.

Gehrels: OK. We're gonna talk about some large numbers here. If you understand exponential notation, the amount of energy that is in these explosions that causes gamma-ray bursts is ten to the power of 45 watts. That's a billion, billion, billion, billion, billion watts. It's a huge number. But to try to put it into terms that are maybe easier to understand, the amount of energy it takes to create these bursts -- and remember, this is all coming out in just a few seconds of gamma-ray flash -- is the same as the energy that our Sun emits over all wavelength bands over its entire lifetime. So it's an unimaginable, huge number.

Englehardt: The next question we have is from Nesanel from Monsey, New York: How often do gamma-ray bursts occur?

Gehrels: Over the whole sky, we believe that they occur several times a day. We don't know for sure, because we've seen only brighter gamma-ray bursts with existing instruments. With Swift, we're gonna look to even fainter levels and maybe we'll see some new kinds of bursts. Swift sees about one-sixth of the sky at any one time, so we will detect a burst about every three or four days. We're gonna see about two a week.

Englehardt: Two a week! The next question we have is from Tim from Seattle. Could gamma-ray bursts be an after-effect from matter and anti-matter colliding together?

Gehrels: Well, that's a very interesting question that he's asking. There are actually over 100 different theories of what could cause gamma-ray bursts. We don't know what causes them. One of those theories is, indeed, anti-matter and matter colliding and annihilating each other. But the most theories right now are based on observations that we have from the Compton Observatory and the BeppoSAX Italian mission with the Dutch instrument on board, is that these gamma-ray bursts are somehow associated with the formation of black holes. We believe that they're the birth cries of black holes that we see throughout the universe and are somehow associated with the death throes of massive stars. Perhaps they collapse and form these black holes and a gamma-ray burst is formed. But we really don't know, and we hope with Swift to find out exactly what causes bursts, and there are various kinds of bursts. We're going to try to understand all the different kinds, also.

Englehardt: OK. The next question we have is from Mustafa from New Jersey: One objective of the Swift mission is to use gamma-ray bursts to study the early universe. How can that be possible, and what does that objective mean?

Gehrels: I think this is really an excellent question. One of the most exciting things that we want to do with Swift is to use gamma-ray bursts to learn about the early universe. Gamma-ray bursts are very penetrating. They're like X-rays, they can go through all kinds of matter. They can go through our bodies. They're even more penetrating than X-rays. And so you can see gamma-ray bursts from across the entire universe. The universe is transparent to gamma rays and these gamma-ray flashes. The things that we'd like to learn about these bursts that have to do with our understanding of the universe is, when did the first stars form? If these massive stars really form early, then they collapse and make these black holes that form gamma-ray bursts and we would see those... Also, by looking at the signal coming at us in the gamma rays, and there's also after the gamma-ray flash, a glowing ember, an X-ray and optical, by looking at that emission, we can learn what the universe was like in its very first efforts.

Englehardt: OK. The next question we've got is from Cheyenne from Dalton. How will it catch the bursts, how long do they last, how fast do they move and how will it affect the spacecraft? I think he meant how will the gamma rays affect the spacecraft?

Gehrels: OK. I think I should describe how Swift detects gamma-ray bursts. I think that's where this question is leading toward. We have onboard a gamma-ray telescope. This is a new technology kind of telescope that is able to make images of the sky, so when a gamma-ray burst goes off we can find out where it occurred in the sky. We then pass that information on to the spacecraft, and the spacecraft quickly reorients itself to point the onboard X-ray and optical telescopes at the position where the burst was. So by studying the X-ray and optical afterglow, we can get the position extremely precisely on the sky. We're talking about arc-second imaging, the kind of imaging you can do with the Hubble telescope -- and thereby we can see exactly where the bursts occur, whether they're inside external galaxies, where in the galaxy they occurred, and this is how we learn about gamma-ray bursts.

Englehardt: OK. The next question we have is from Johnson from South Windsor. Will the X-ray telescope be the most powerful X-ray telescope in our history?

Gehrels: The X-ray telescope, our XRT instrument onboard Swift, will not be the most powerful instrument that's flown. In fact, there are two telescopes right now that are in orbit that are more powerful: the Chandra Observatory, which is a NASA mission, and the XMM-Newton X-ray Telescope, which is from the European Space Agency. But the XRT is a very powerful and beautiful instrument, and in fact, it's the most sensitive X-ray telescope that's ever made rapid observations right after a gamma-ray burst like this. So it's the kind of telescope that's good for rapid observations after a gamma-ray burst, but not the biggest one that's ever flown.

Englehardt: Makes sense. The next question we have is from Rick from Cincinnati, and he says: The streaming video from Swift shows several different colored coverings -- reflective gold at the bottom, a band of reflective silver in the middle and dull gray at the top. What are their different purposes?

Gehrels: Well, Rick is very observant. In space, you can either be extremely hot or extremely cold. There's no atmosphere to mediate the temperature, so when you're in the Sun, the instruments get extremely hot. And when you're in the shade, it's cold. We cover the spacecraft and the instruments with thermal blankets. These are blanket materials that have metalized surfaces over them, and the surfaces have different coatings on them depending on if you want to keep things hot or cold. Gold foils tend to reflect the sunlight and keep the sunlight from heating up that part of the spacecraft. White surfaces radiate well and can get rid of heat. And then we have blanket material underneath when we want to keep things warm. So that's what you're seeing when you see the Swift spacecraft. You're seeing these blankets with their foils and metal covers.

Englehardt: OK. The next question we have is actually a composite from two different people that had similar questions. One is Morris from Surprise and then Nathaniel from New York. They want to know, how long will Swift remain active and what is the follow-on to it?

Gehrels: Swift has a nominal lifetime of two years. We'll be able to measure more than 200 gamma-ray bursts in those two years and really solve the gamma-ray burst mystery. But it will be in orbit for longer than that. It'll be in orbit for eight years or longer, and so we hope to be able to operate it for all of those years and study hundreds of gamma-ray bursts. The follow-on to Swift is a NASA satellite that's a large gamma-ray observatory called GLAST. It will fly in 2007 and it will perform gamma-ray burst studies, although it also will do other kinds of gamma-ray astronomy.

Englehardt: OK. Our next question is from Robert from New York: If Swift exceeds its expected life, is it possible to maintain, repair or replace parts with the space shuttle or the next generation of them?

Gehrels: Swift was not designed to be serviced like the Hubble Space Telescope by astronauts. We have to design the mission extremely robust in the beginning so it will last this time without any kind of repair work by astronauts. And so, once we launch it, it'll be up there and hopefully operating on its own for these eight years.

Englehardt: I hope so too. The next question we have is from Junichi from Japan: As I know gamma rays do a lot of harm to life, how dangerous are gamma-ray bursts from somewhere in the universe?

Gehrels: Gamma rays from, can damage a human body if you're exposed to a high rate of them. For instance, if there's a radioactive source or medical source that emits gamma rays, you want to keep it wrapped in lead and not near a human. But the gamma rays that we see from a gamma-ray burst are very low level, and also, we're protected by the atmosphere of the Earth from these gamma rays, so that we don't actually have any danger to humans from gamma-ray bursts. Now it is true that the explosion that produces these bursts is so powerful that if it occurs near a planet like the Earth, it'll strip the atmosphere right off the planet. So that would be, you know, tremendously dangerous, in fact it would cause extinctions to life on this planet. You don't have to worry, that won’t happen. It's very low probability that that would happen for our Earth, that there would be a gamma-ray burst so close. It may have happened sometime during our history of the Earth. It's very possible that it caused an extinction of some life forms on the Earth. But it's an interesting subject nevertheless, because there are gamma-ray bursts going off, there presumably are planets in those galaxies that they're going off by, going off in, and so those planets are being affected by these bursts. And it's a factor in trying to understand how much life and how many life-bearing planets there may be in the universe.

Englehardt: Wow. That's interesting. Our last question is also from Junichi, and he asks: The most well-known gamma rays come from solar activities which threaten the astronauts on the International Space Station and sometimes does much damage to the computers of satellites. What is the difference between these gamma rays and gamma-ray bursts from the unknown universe?

Gehrels: OK, so this is another question that has to do with the affect of gamma rays on people, which is, of course, quite an interesting subject. There are solar flares, large flares on the surface of the Sun, that emit gamma rays, and they come throughout our Solar System. When there's a solar flare, there are also particles that are emitted from the Sun. It's those particles that are more damaging to astronauts and to life than the gamma rays themselves. As I mentioned earlier, gamma rays can cause medical problems, but only in very high dose rates. It is more the particles that come from the solar flares. Since the gamma-ray burst sources are so far away in distant galaxies, we don't see the particles from the gamma-ray bursts coming to the Earth. They're absorbed in the universe, they never get to us. And so, a gamma-ray burst has no effect, would have no effect on astronauts, even if they were exposed to one. It's really the particles from the solar flares that are much more threatening.

Englehardt: OK. Well, thank you for all of your insight today, Neil.

Gehrels: I enjoyed it. Thank you.

Englehardt: As I mentioned earlier, we have a question board winner to announce, and the winner is Mustafa from New Jersey. Congratulations to Mustafa, and Mustafa will receive a mission gift pack. Everyone else whose questions were read will also receive a prize.

That's the end of today's webcast for Swift and its quest to study gamma-ray bursts. Join us again tomorrow at 4 p.m. Eastern Standard Time for a special behind-the-scenes look at Launch Pad 17-A with NASA launch manager Omar Baez. Delta weather officer Joe Tumbiolo will also be here to give us an up-to-the-moment launch day weather forecast, and NASA launch director Chuck Dovale will walk us through the final preparations for the launch and answer some of your questions. Many thanks to our guests for their expertise, and thanks to all of our viewers for joining us and submitting all of those great questions.

Don't forget, you can track the launch of Swift live from our Virtual Launch Control Center, which begins approximately one hour prior to launch and offers continual mission coverage after launch. Visit Swift! I'm Rex Engelhardt, and we'll see you next time.