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Wednesday, 18 October, 2000, 14:37 GMT 15:37 UK
Scattered spacecraft pinpoint cosmic burst
Ulysses looks out for gamma bursts from deep space
By BBC News Online science editor Dr David Whitehouse

Four spacecraft have detected the afterglow of the most distant gamma-ray burst ever recorded, allowing the radiation to be traced back to its origin.

The 11-billion-year-old cosmic explosion could give scientists a new way to measure the age of celestial objects, said astronomers.

The observations were made by a cluster of probes called the Interplanetary Network.

They have revealed that the burst probably came from a gigantic dying star more than 30 times the mass of the Sun and which exploded when the Universe was about one tenth of its present age.

"Detection of gamma-ray burst GRB 000131 at an extremely high red shift of 4.5 corresponds to a distance of about 11 billion light-years away," said Kevin Hurley, a physicist at the Space Sciences Laboratory of the University of California, Berkeley.

A Hubble Space Telescope view of the afterglow of a burst
"The light from this gigantic flash had travelled 11 billion years before reaching the Earth, and suggests that these explosive objects may provide us with the longest yardsticks yet for detecting and studying galaxies in the early Universe."

Gamma-ray bursts are mysterious flashes of high-energy radiation occurring about once a day somewhere in the sky. Their origin remains a mystery, although most astronomers believe the bursts come from enormous explosions that occur far across the Universe.

Only recently has enough evidence been accumulated to link the longest of these bursts to hypernovae. These are giant, extraordinarily intense and unusual supernovae, which are dying stars that collapse under the weight of their own mass.

Gold medal

At their peak, the bursts are by far the brightest emissions of gamma-ray radiation in the sky, Hurley said.

Before these observations were recorded, the most distant gamma-ray burst to be detected was GRB 971214, estimated to be less than 9 billion light-years away.

"If this were the Olympics, we'd have the gold medal now," said Hurley, who runs the network of spacecraft that carry detectors.

"Still, the fact that such a faint, distant source can produce a burst of gamma rays which appears to be of more or less average intensity from Earth hasn't been explained yet."

The spacecraft that detected this burst were the Ulysses spacecraft, the Near Earth Asteroid Rendezvous (Near-Shoemaker) craft, the Wind spacecraft, and the Italian Bepposax spacecraft.

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