The most energetic events in the universe

They are more powerful than any cosmic explosion since the Big Bang. When first discovered 30 years ago they were thought to be Russian nuclear bomb tests in space. Now, we know that the hugely powerful cosmic explosions, the largest in the universe, are bursts of gamma radiation. They come from galaxies so far away that their light takes billions of years to reach us. But the origin of the gamma-ray bursts remains one of the great riddles of the universe.

One theory is that the violent flashes which occur once or twice a day take place when a black hole swallows another star. A gamma-ray burst originating in our part of the Milky Way, within 1,000 light-years or so, could lead to mass extinction on earth. This might explain the demise of the dinosaurs.

The picture shows NASA's impression of how they might have seen the beginning of the end of their reign on earth. There is another fascination for scientists. The explosions can act as beacons, briefly revealing parts of the universe so distant that they lie beyond the reach of any telescope on earth. Observations could give us a new insight into how the universe was formed as well as how stars die.

United Kingdom space scientists, working in partnership with United States and Italian teams, hope to solve the puzzle. They constructed two specialist telescopes for NASA's Swift Gamma-Ray Burst Explorer. Although the gamma rays fade away in seconds, the telescopes will enable astronomers to catch a glimpse of their afterglow of X-rays and visible light.

During its three-year mission starting in 2003, Swift will also hunt for new black holes and other sources of cosmic gamma-rays.

According to Professor Alan Wells, director of the Space Research Centre at Leicester University, the mysterious flashes have been detected by satellites for 20 years but only recently has one been imaged optically. "The gamma-ray burst has been tracked down to a galaxy that is located more than half-way to the edge of the observable universe. Although a gamma-ray flash lasts for only a few seconds, during that time it far outshines an entire galaxy of stars, making these phenomena the most energetic events in the universe, producing far more energy than even a supernova explosion", Professor Wells said."

Photo: NASA