Nasa peers back into the 'cosmic dark ages'

A massive gamma-ray burst 13 billion light years away has thrown new light on the early years of the Universe
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The Independent Online

The most distant object ever observed in space has provided scientists with an unprecedented insight into the "cosmic dark ages" following the birth of the Universe some 13.7 billion years ago.

A gigantic explosion on the edge of the known Universe has been confirmed as the furthermost object in the cosmos. It occurred nearly 700 million years after the Big Bang and its radiation has taken some 13 billion years to reach Earth – making it 13 billion light years away.

The explosion is one of many thousands of gamma-ray bursts that scientists have detected since they were first discovered more than 40 years ago by spy satellites designed to monitor the radiation emitted by man-made nuclear explosions. This particular gamma-ray burst, named 090423, occurred on 23 April and its afterglow lasted for about 10 seconds before it died out. This was long enough for the Swift satellite operated by Nasa to identify its location so that other telescopes on the ground could analyse the explosion in more detail.

Gamma-ray bursts are the most energetic events known to scientists. In just a couple of seconds these massively powerful explosions in space release as much energy as the Sun would release in its entire lifecycle of 10 billion years. Finding a gamma-ray burst that is 13 billion light years away means that it must have taken place within the period known as the "cosmic dark ages", a timespan of about 900 million years that separates the Big Bang from the formation of the earliest stars and galaxies.

"This observation allows us to begin exploring the last blank space on our map of the Universe. It's the first time that we've seen an object within this period of the Universe's dark ages," said Nial Tanvir, of Leicester University, who led the study published in the journal Nature.

"We're beginning to peer back to the era of the very first structures in the Universe. It's the last unexplained era because in broad-brush terms we have a reasonably good idea of what happened during the rest of the life of the Universe," he added.

Gamma-ray bursts, named after the intense amounts of gamma radiation they release, are believed to occur when massive stars some 50 or 100 times bigger than the Sun are swallowed up by a newly formed black hole, which results in the instant conversion of matter into energy.

Astronomers believe that as the black hole swallows up the dead star, intense jets of gas punch their way through the stellar material, forming interactions with other stellar gases previously shed by the dying star, causing it to heat up and release short-lived after-glows of radiation, which can be detected and measured by astronomers on Earth.

Andrew Levan, of Warwick University, another member of the international research team, said that the very ancient age of the gamma-ray burst detected in April meant that the dying star that formed it must be one of the first to be created in the early Universe.

"We're looking back into the Universe when it was very, very young and we're seeing objects that formed in the very early Universe – it was one of the first objects to form after the Big Bang," said Dr Levan.

"We thought that there were possibly stars there during this epoch but we've not until now seen them before. These early stars only lived for a few million years. They lived fast and died young," he added.

The explosion of gamma-ray burst 090423 occurred when the Universe was less than 5 per cent of its present age and a tenth of its present size.

Big Bang: Understanding the birth of the Universe

Q. Why do we think the Universe was created in a "Big Bang"?

A. Theoretical cosmologists have predicted the existence of a Big Bang for about 50 years – the theory owes its name to the late Sir Fred Hoyle, who didn't in fact believe in such a sudden beginning. However, astronomers have now made categorical observations that support the theory, including the discovery of the remnant "background radiation" left behind from the Big Bang, which now pervades the Universe.

Q. How do we know that the Big Bang occurred 13.7 billion years ago?

A. One way is to measure the speed at which the Universe is expanding and to calculate something called the Hubble constant with great accuracy. The Hubble Space Telescope did in fact do this and the calculations showed that the Universe has been expanding for about 13.7 billion years, hence the age of the Big Bang.

Q. How do gamma-ray bursts fit into the story of the Universe?

A. These are massively powerful explosions, the most energetic events known to science. They were first discovered in the 1960s by American Vela spy satellites designed to detect Soviet atomic tests. Gamma-ray bursts are thought to be the result of newly-formed black holes swallowing up massive dying stars more than 50 times the size of the Sun. So, gamma-ray bursts occur when a dying star disappears into a black hole releasing vasts quantities of energy in the form of radiation. As such they have always existed for a long as there have been stars.

Q. Will we ever see to the edge of the Universe and what lies beyond it?

A. Astronomers are seeing further and further back in time by observing objects that are further and further away from the Earth. They hope to get very close to the Big Bang but there will almost certainly be some limit on how far back they can look – perhaps these earliest objects are just too small to ever see. What happens beyond the Big Bang is largely a mystery, and a subject that cosmologists will speculate on endlessly for they are well known to be often in error, but never in doubt.

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