Found: the blast at the beginning of the universe

John von Radowitz
Thursday 26 May 2011 00:00
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Astronomers may have detected the most distant and ancient object ever seen, a massive explosion that lit up the early universe soon after its birth. When the blast, known as a gamma ray burst (GRB), detonated, the universe was less than 4 per cent of its present age and 10 per cent of its present size.

Light from the event has taken 13.14 billion light years to reach the Earth. It began its journey only about 600 million years after the Big Bang that created the cosmos. The source of the burst, designated GRB 090429B, was an exploding star which for a brief time shone a million million times more brightly than the Sun. Its fading "afterglow" was detected by the American space agency's Swift satellite in April 2009.

Two years of analysis have now shown the object to be a candidate record-breaker. British astronomer Dr Andrew Levan, from the University of Warwick, who was among the first to view the explosion, said: "The race to find distant objects stems from the desire to find and study the first stars and galaxies that formed in the universe, in the first few hundred million years after the Big Bang.

"By looking very far away, because the light takes so long on its journey to reach the Earth, astronomers are effectively able to look back in time to this early era.

"Unfortunately, the immense distances involved make this very challenging. There are different ways of finding such objects, looking at distant galaxies being the most obvious, but because galaxies are faint it is very difficult. GRB afterglows are so much brighter." His American colleague Dr Derek Fox, from Pennsylvania State University, said: "The galaxy hosting the progenitor star of GRB 090429B was truly one of the first galaxies in the universe." The discovery will be reported in a forthcoming edition of the Astrophysical Journal.

GRBs, which emit powerful blasts of gamma rays, are the most violent explosions known, and occur somewhere in the observable universe at a rate of about two a day.

Because of their extreme brightness they can be detected even at distances of billions of light years. While the bursts themselves last for minutes at most, their fading "afterglow" light lingers on and remains observable for days or even weeks.

GRB 090429B erupted for less than 10 seconds and produced a relatively faint X-ray afterglow. Further calculations have to be made before astronomers can confirm that the burst really is the most distant object in the universe. Other recent contenders for the title include a dim and distant galaxy that might be between 13.11 and 13.28 billion light years away.

Professor Nial Tanvir, from the University of Leicester, part of the Hubble Space Telescope team that made follow-up observations of GRB 090429B, said: "This GRB shows us that there is a lot of action going on in the universe which we can't currently see. Our observations show us that even the Hubble Space Telescope is only seeing the tip of the iceberg in the distant universe."

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