Plait: So Dr. Gehrels, I've been hearing a lot about very distant gamma-ray bursts. What can you tell us about how Swift is helping us find these objects?

Gehrels: Swift is very sensitive for faint gamma-ray bursts and so we were anticipating even before launch that we would see bursts from far away. And the results have been quite surprising and mind-boggling. We've seen bursts now that are coming from virtually the very edge of the universe. They're more than 10 billion light years away, and formed when the universe was just beginning to make stars and galaxies and structure in the universe. What's been so surprising about these results is that those bursts at the very highest distance are not at all the faintest ones. Some of those are really blasting powerful gamma-ray bursts and how is it possible that there is an explosion so far away that it's making radiation we can see so brightly here. Well, that's a puzzle for the theorists, and they're working on it. I can tell you what our observations are like. On September the 4th of 2005 we detected a gamma-ray burst. We got observations with Swift of the gamma-ray emission, the X-ray emission, and an optical afterglow. And then large telescopes looked in that direction, and at first they didn't see any emission, and we were wondering what kind of burst this was. And it's because we were looking in the visible band. With these large telescopes then looked at redder colors and into the infrared. They saw that this was a bright afterglow. And this was the first signature that this was extremely high distance. We expect the radiation coming from these high distances to be redshifted. It's by the Hubble Law. And so they're very highly redshifted. And you expect to see them only in the infrared and the optical. So that was a really neat event, and it turned out to be 12.6 billion light years away. It was by far the record largest distance burst we've seen. 

Plait: Do you expect to find any in the nominal Swift mission - as its orbiting the Earth and still working - do you expect to find any further away than that. What are the theorists tell you about those? 

Gehrels: We do expect to see them. In fact the great hope is the most interesting thing we could do - would be a huge discovery - would be to get a gamma-ray burst from one of the first generation of stars in the universe. There's a name for those, they're called Population III stars. They'd be very different from any other stars we know of because the early universe only had hydrogen and helium and a little bit of heavier elements, but very few. And so these first stars were quite different than our stars now which are a mix of all different kinds of elements. These were almost pure hydrogen and helium stars. People have theorized that there are such stars. The only way that you could see them directly would be when they explode. That's the only time they would be bright enough. So, our hope is we can find a Population III star exploding, producing a gamma-ray burst. 

Plait: Well that's pretty cool. So in other words, we can't see them forming, we can't see them when they're alive, but only when they die is the only chance we get to detect these things. That's pretty interesting all by itself. 

Gehrels: Yeah, that's right. We see the death cries of these stars. They live very short livetimes - sort of million-year lifetime - and so you'll see it very soon after it was born. But you indeed...that's what produces gamma-ray bursts. When stars end their lifetime - not all stars explode but the most massive stars explode - and some of those make these flashes of gamma rays. It's really a very intersting topic.  

Plait: Well, we can hope that sometime during the Swift mission then we'll get a glimpse of some of these first stars that were born in the universe. That would be a tremendous discovery. Thank you very much, Dr. Gehrels. 

Gehrels: My pleasure.