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Astronomers witness earliest ever star death

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Astronomers have identified the most distant ever gamma ray burst, a cosmic event that took place when the universe was a mere 900 million years old, less than seven per cent of its present age.

A team of Italian astronomers made the final observations with the ESO Very Large Telescope, and was able to confirm that the burst took place approximately 12.7bn years ago.

"This also means that it is among the intrinsically brightest Gamma-Ray Bursts ever observed", said Guido Chincarini from INAF-Osservatorio Astronomico di Brera and University of Milano-Bicocca. "Its luminosity is such that within a few minutes it must have released 300 times more energy than the Sun will release during its entire life of 10,000 million years."

Gamma ray bursts (GRBs) are widely thought to be caused by the collapse of supermassive stars into black holes. They are the most violent events ever to have occurred in the universe, aside from the big bang itself.

Researchers are particularly interested in GRBs because they give an indication of when stars began to evolve in the universe: if there is a gamma ray burst, the implication is that stars must have existed long enough for one to collapse into a black hole.

The explosion was first spotted by the Swift observatory on 5 September. Swift is set up to detect gamma ray bursts. It can respond to an initial detection within seconds, and will also alert ground-based observers.

In this case, the first telescope on the case was the Palomar Robotic 60-inch Telescope, which couldn't see the afterglow in the visible portion of the spectrum. Because of the physical limits of the telescope, this means the light from the explosion must be at least a million times fainter than something that could be seen with the naked eye.

Another team of observers found the afterglow shining in the near-infrared J-band at magnitude 17.5, at least 25 times brighter than the visible light. Further observations ruled out the possibility that the intervening space is filled with enough dust to significantly affect its magnitude, leading the astronomers to conclude that the burst must be one of the most distant ever recorded.

Italian astronomers then used the ESO (VLT) array to confirm the findings, some 24 hours after the initial detection. They made observations in four spectrum bands, from the visible through to the near infrared.

This allowed them to calculate a redshift of 6.3 for the object (redshift is a measure of how fast something is moving away from us) which conclusively dates the explosion as being some 12.7bn light years distant. ®

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