Starburst `on edge of time' stuns scientists

EVEN seasoned astronomers have been stunned by the discovery of a starburst that was, briefly, as bright as the entire universe - and constituted the most powerful explosion since the moment of creation in the Big Bang.

Any living thing in the same galaxy may have been killed outright. Fortunately for us, the explosion occurred almost at the edge of time, in a galaxy 12 billion light years away.

Over just a few seconds, a burst of gamma rays was emitted by some stellar event - which is still not understood - that released as much energy as our entire galaxy, the Milky Way, puts out in 200 years.

Professor Shrinivas Kulkarni, one of the team of scientists from the California Institute of Technology (Caltech) in Pasadena who made the discovery, said: "The energy released ... staggers the imagination."

Professor George Djorgovski, another member of the team, which today announces its discovery in the science journal Nature, said: "For about one or two seconds, this burst was as luminous as all the rest of the entire universe."

Gamma-ray bursts are mysterious flashes of high-energy radiation that appear at random and typically last only a few seconds. They are not visible to the human eye, but can be detected by radio telescopes.

No one knows what causes them, but astronomers generally agree they must be connected with the death of very massive, short-lived stars such as "neutron" stars. One theory being suggested for this latest event is the collision of two neutron stars - which are enormously dense, dead stars which are not quite large enough to have collapsed into black holes. Neutron stars are so dense that a spoonful of material from one would weigh 100 million tonnes. Black holes are points of infinite density from which nothing can escape.

All gamma-ray bursts are immensely powerful, but none of the several thousand detected so far come close to the one described in Nature.

A British expert on gamma-ray bursts, Dr Ralph Wijers, from Cambridge University, said gamma-ray bursts were thought to occur only once every 100 million years in a galaxy such as ours.

However, if one did occur within even a reasonable astronomical distance from Earth, the result could be apocalyptic. The intense radiation would not be detected until it reached us, and then it would be too late. "People have speculated, for example, that nearby supernovae [exploding stars] can cause mass extinction, and gamma-ray bursts put out even more energy in a similar form," said Dr Wijers, adding that such bursts were "very rare".

Luckily the explosion, designated GRB 971214, was so distant that not even a blast as bright as the universe poses any threat to the Earth.

The light arriving from the gamma-ray burst would have started its journey when the universe, thought to be about 14 billion years old, was in its infancy.

GRB 971214 was first detected last December, by two orbiting satellites. As the afterglow from the burst faded, the Caltech team detected an extremely faint galaxy at its location.