Gamma Ray Bursts

3/30/08 – 4/5/08
by C. Zaitz

Even though we think of the sky as having countless stars, it turns out we can only see several hundred of them due to light pollution. In fact, our Milky Way galaxy contains several hundred billion stars. Only in very dark skies can you see anything beyond the Milky Way. Until recently, our sibling galaxies, the Triangulum and Andromeda, were the most distant objects visible to the naked eye, at a distance between two to three million light years. Recently, something even more distant was seen. Though it was only slightly brighter than the faintest stars visible to us, it was very distant, and very old, light. At a staggering seven and a half billion light years away it was still seen, if even for seconds, and if you knew where to look.

What was this fleeting image? It was a bright gamma ray burst. Gamma rays are the most energetic form of “light” or electromagnetic energy. Gamma rays are produced by all stars, but when a huge star dies, it often produces prodigious amounts of them as it collapses. Astronomers think that these gamma ray bursts we see all around us are the relics of the deaths of some of the very first stars formed in the early universe. When they die, they go out with a big flash.

The incredible thing about gamma bursts we detect is that they are all very distant, but incredibly powerful and bright, much brighter than anything known in the universe. But they are not bright in all directions. The reason they can show up looking so luminous after seven and a half billion years of travel in a stretching universe is because the energy is bundled into relatively narrow columns. The energy streams out like a beacon from a lighthouse and if earth happens to lie along its route through the universe, we will catch a glimpse of it.

Astronomers are very interested in spying gamma ray bursts because they could tell us more about the early universe. Bursts of high energy rays are very harmful to humans, so it’s providential that air stops gamma and x-rays from getting to us. But it also makes them hard to find. Currently NASA has a telescope in orbit called Swift that scans the universe for gamma ray bursts. The problem with gamma rays is that they are much more energetic than visible light waves, and they don’t give a very accurate image of what they are detecting. It’s like trying to draw a picture using a shotgun rather than a pencil. In order to pinpoint where the bursts come from, we have to coordinate space and earth telescopes. So astronomers on earth are tied into Swift’s detectors. Once the gamma rays are detected, astronomers know about it and telescopes on earth can search the same area for visible light, which sometimes accompanies the bursts. Once we find them, we can study the information the bursts give us and map them.

Even though the bursts aren’t around for long, they do give us an incredible look at our past, into a time where the universe was dominated by giant hydrogen stars and was much smaller than it is today. It’s a universe that is continually changing, and revealing itself to us a burst at a time.