#2611 Feature: The Space Environment

Hunting for Gamma Rays

PHIL PLAIT, Astronomer: "A gamma ray burst is surprisingly, a burst of gamma rays. Gamma rays are extremely high-energy forms of light. Itís a photon, just like regular light, but just has a lot more energy. It takes an extremely violent event to generate light of this energy. And thatís what a gamma ray burst is---itís an enormous explosion---huge, vast, words fail when you try to describe how much energy is in these things. And they generate a beam of gamma rays that shoots out and can travel clear across the universe, and we can detect those here on Earth."

Gamma rays are invisible to human eyes, so until the invention of special gamma ray detectors in the last century, scientists had no idea that gamma rays existed. Bursts of gamma rays are even more elusive. Even though there are hundreds of bursts every year, they occur with no warning in random parts of the sky, and they last just a few milliseconds. For astronomers itís difficult to pin down a gamma ray burst long enough to take its picture. Using Earth-based telescopes, itís downright impossible!

PHIL: "It turns out that detecting gamma ray bursts isnít so easy. For one thing, you have to go above the earthís atmosphere. Even though these things can travel hundreds of millions, or even billions of light years, the earthís atmosphere absorbs them. And so they travel all that way to here, and in the last few miles, they can get absorbed by our atmosphere. And so we have to go above the earthís atmosphere and look out. And thatís the only way to see them."

To get an unblocked view of gamma ray bursts, the orbiting Swift Observatory will carry three telescopes above the earthís atmosphere.

The main one is a gamma ray detector. Itís called the BAT for Burst Alert Telescope. Within 15 seconds of detecting a flash from a gamma ray burst, the BAT will direct the entire satellite to swing into action and bring the burst area into the vision of the other telescopes. The swift action should help the observatory to succeed where slower moving telescopes have failed---to catch a gamma ray burst as itís happening. By studying gamma ray bursts in progress, astronomers hope to answer some basic questions about these explosive events---what exactly are they? What causes them? Where do they happen? What can they tell us about the birth and development of our universe?

Before the Swift Observatory can start solving cosmic puzzles, it has to make the move out of the design lab and into Earth orbit---an environment thatís harsher than it looks.

PHIL: "When you go out at night and you look up with your eyes, you donít see things changing, or not very much at least, and it looks very peaceful and calm, and itís really anything but. The universe is an extraordinarily violent place; gamma ray bursts are a pretty good indication of that. The environment of space, even near-earth space, is also very difficult. Here on earth, weíre used to nice atmosphere and we can breathe and the temperatures donít change that much day-to-day, but out in space thatís not true."

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