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Cosmic distance record 'broken'

A cataclysmic explosion of a huge star near the edge of the observable Universe may be the most distant single object yet spied by a telescope.

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The blast may have occurred a mere 520 million years after the Big Bang

Scientists believe the blast, which was detected by Nasa's Swift space observatory, occurred a mere 520 million years after the Big Bang.

This means its light has taken a staggering 13.14 billion years to reach Earth.

Details of the discovery will appear shortly in the Astrophysical Journal.

The event, which was picked up by Swift in April 2009, is referred to by astronomers using the designation GRB 090429B.

The "GRB" stands for "gamma-ray burst" - a sudden pulse of very high-energy light that the telescope is tuned to find on the sky.

These bursts are usually associated with extremely violent processes, such as the end-of-life collapse of giant stars.

"It would have been a huge star, perhaps 30 times the mass of our Sun," said lead researcher Dr Antonino Cucchiara from the University of California, Berkeley.

"We do not have enough information to claim this was one of the so-called 'Population III" stars, which are the very first generation of stars in the Universe. But certainly we are in the earliest phases of star formation," he told BBC News.

Swift, as its name implies, has to act quickly to catch gamma-ray flashes because they will register for only a few minutes.

Record breaker Fortunately, an afterglow at longer wavelengths will persist for much longer, sometimes days, which allows follow-up observations by other telescopes that can then determine distance.

It was this afterglow analysis that established another burst in the week previous to GRB 090429B to be at a separation from Earth of 13.04 billion light-years, making it temporarily the "most distant object in the Universe".

This other event (GRB 090423) was reported fairly soon after its occurrence, but it has taken astronomers two years to come back with a confident assessment that an even greater expanse lies between Earth and GRB 090429B.

There are other competing candidates for the title of "most distant object". Hubble, for example, was given much more powerful instruments during its final astronaut servicing mission in 2009, and teams working on new images from the famous space telescope have seen galaxies that look not far short of GRB 090429B - and potentially even further out.

It should be stated, of course, that in these sorts of observations, there is always a degree of uncertainty.

Hubble's targets were galaxies - collections of stars; and GRB 090429B is the signature of a single event, a single star. So, in that sense, it might be considered apart.

Scientists are very keen to probe these great distances because they will learn how the early Universe evolved, and that will help them explain why the cosmos looks the way it does now.

They are particularly keen to trace the very first populations of stars. These hot, blue giants would have grown out of the cold neutral gas that pervaded the young cosmos.

Read on



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