From beyond the back of

If some recent findings hold water, the mysterious gamma ray blasts emanate from the most distant celestial objects

 
Published: Friday 31 July 1998

gamma ray blasts are among the most enduring puzzles in astronomy. The flashes of gamma rays -- seen randomly in the sky about once a day -- provide no clues about the distance they travel and their source. There have been several estimates and models of the distance of the objects from which these bursts emanate. A recent estimate puts the origin of one such burst about 10 billion light years away. If this is true, then the sources of these bursts are among the farthest objects known to us and the bursts are the most energetic ones in the universe. These are the findings of a team of astronomers at the California Institute of Technology ( cit ), usa .

Gamma rays are at the high energy end of the electromagnetic spectrum. These bursts, which vary in duration from a few milliseconds to minutes or hours, are seen without any coincidental flash of light or any other signal. With the launching of Beppo- sax , an Italian-Dutch project which had two wide field x -ray cameras that operate in conjunction with the gamma ray detectors, the whole field of gamma ray astronomy received a shot in the arm. Using satellite data, it is now known that the origin of the gamma ray bursts is not galactic -- the events producing these bursts are not within our galaxy.

On December 14, 1997, one gamma ray burst was detected by the Beppo- sax satellite. With the x -ray cameras on the satellite, the location of the bursts has been narrowed down substantially, giving the optical and radio telescopes a better chance to find them. The team at California used the 10-metre Keck telescope in Hawaii and the Hubble Space Telescope to pinpoint the part of the Universe from where the gamma rays seemed to be coming. Once this was done, the Keck telescope was used to obtain the spectrum of the galaxy from which the burst was coming.

The spectrum of any object in space tells us not only about the composition of the object but also gives us an idea of how far the object is from us. In the expanding Universe, light emitted by celestial objects is shifted towards the red part of the spectrum as they move away from us. This is known as the Doppler shift, which is familiar to the change of pitch of the whistle from a moving train. With the red shift, the astronomers calculate the distance of the light-emitting object.

This distance measurement is significant because the usual theory of gamma ray bursts is of a cataclysmic event (usually the collision of two neutron stars) producing the awesome energy observed. If the distance reported by the cit is correct, then the event would have to produce an extraordinarily large amount of energy to be observed by us. The theorists are now busy checking out how their models fit with the new measurements. With better data, the solution to one of the most enduring mysteries in astrophysics is much closer.

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