Telescope pinpoints gamma-ray bursts

January 16, 1994|By Boston Globe

WASHINGTON -- A group of astronomers reported yesterday that bursts of energy that have been seen by an orbiting telescope may be, for the few seconds they last, the brightest objects in the universe.

The bursts may also provide the first confirmation of a peculiar effect, predicted by Einstein's theory of relativity, called "time dilation."

The short-lived events are known as gamma-ray bursts -- brief, unpredictable eruptions of the highest-energy form of electromagnetic radiation that last from fractions of a second to a few minutes. Gamma rays are similar to X-rays but have a higher energy level.

The existence of gamma-ray bursts has been known since 1979, but until now there had been disagreement over where the energy comes from. It was unclear whether the objects might have been nearby and relatively dim, or very far and bright.

The latest evidence, presented yesterday at a meeting of the American Astronomical Society, indicates that whatever is causing these bursts is very far away -- about 8 billion light years, or halfway to the limits of the known universe.

The evidence comes from a space telescope called the Gamma Ray Observatory, which was launched in 1991. It has detected about 900 of those bursts and has found that they come apparently at random from all parts of the sky. One burst can produce more energy in a few seconds than the sun emits in 1,000 years.

Jay P. Norris, an astronomer at the National Aeronautics and Space Administration's Goddard Space Flight Center in Greenbelt, said that he and a team of researchers had found that the fainter those bursts were, the longer they lasted. In addition, the fainter bursts have a longer wavelength than the brighter ones.

Those observations, he said, confirm a predicted effect of relativity called time dilation, a stretching of the signal caused by the distance it travels. It also shows, he said, that the fainter objects must be as far away as some of the most distant galaxies.

Nobody knows exactly what produces these bursts, but researchers said it must be an extraordinary cataclysm, like a collision between two black holes.

"This is a great result," said Bohdan Paczynski of Princeton University, who was not involved in the research. He called it "one of the most spectacular astrophysical discoveries of the decade."

Robert Nemiroff, an astronomer at George Mason University who was part of the team that analyzed the bursts, said, "This is not only an important discovery about gamma-ray bursts; it is a discovery that gamma-ray bursts may be able to tell us about distant parts of our universe."

The astronomers cautioned that the analysis was preliminary and that there might be other reasons for gamma-ray intensity and duration.

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