Spacecraft is to study explosions in space

British scientists hope to solve the mystery of gamma bursts soon, writes Alison Goddard.

When a burst of gamma rays was detected in the sky in 1967, scientists at the Los Alamos laboratory thought that it was due to covert nuclear weapons testing.

The discovery was not reported to the world until 1973, by which time many such bursts had been picked up by satellites designed to look for violations of the Nuclear Test Ban Treaty. The data showed that what could have been nuclear explosions turned out to come from outer space.

More than 30 years later, gamma ray bursts continue to baffle scientists. Now astronomers at the University of Leicester and University College London hope to launch a spacecraft called Swift to learn more about them in collaboration with US colleagues.

The Particle Physics and Astronomy Research Council has promised more than Pounds 3 million. Nasa has paid for a full engineering and technical design study and in October it will decide whether to take the idea through to launch in 2002.

Gamma ray bursts are the most violent events in the universe. The explosions are so vast that for the few seconds they last, they outshine the whole of the rest of the universe. They happen roughly once each day at random points on the sky and can last from a fraction of a second to minutes.

Swift will have three telescopes to examine gamma rays and the lower energy X-rays and ultraviolet and optical light coming from the explosions. It will be able to swing round within a minute to study any reported burst.

"With the ability to turn rapidly towards active bursts, Swift will be able for the first time to examine the dynamic process of the burst events and answer fundamental questions about the structure and evolution of the universe," says Alan Wells of the University of Leicester, who leads the UK side of the project.

Two years ago, a mission called Beppo Sax picked up a gamma ray burst which had an afterglow, thought to be produced by the interaction of an ultra-relativistic blastwave with the interstellar or intergalactic medium. Swift will be able to study the evolution of gamma ray bursts and their afterglows over days and months, says Dr Wells.

At present, there are three main competing theories: a collision between two extremely dense and compact stars, called neutron stars; a neutron star merging with a black hole; or a hypernova - the sudden collapse of most of a massive star into a rapidly spinning black hole.