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Last Updated: Monday, 10 April 2006, 16:04 GMT 17:04 UK
Telescope looks to go to the edge
By Jonathan Amos
BBC News science reporter, in Leicester

Artist's impression of Swift (Nasa)
Swift is detecting about two GRBs a week
The Swift telescope is about to break the boundaries of our cosmic vision, to see the most distant objects ever recorded, its chief scientist believes.

The Nasa space observatory has already looked nearly 13 billion light-years across the Universe to record the light from a cataclysmic star explosion.

But Dr Neil Gehrels expects Swift to see even more distant events.

The investigator says the telescope has the ability to observe perhaps the very first stars to shine in the cosmos.

"That's the great hope," he told the UK's National Astronomy Meeting (Nam), hosted this year at Leicester University.

Leicester is a major partner in the Swift mission - it helped to build one of its key instruments - and Dr Gehrels came to the Nam to review the satellite's first full year of observations.

Too young?

The spacecraft is set up to catch gamma-ray bursts - the intensely bright but fleeting flashes of very high-energy radiation that signal some of the Universe's most violent happenings.

Once detected, the observatory swings itself to look directly into a flash with X-ray and ultraviolet/visible telescopes. It will also call up other space and ground-based facilities to join the fray.

On 12 September last year, Swift caught the gamma-ray burst (GRB) from what was probably the death throes of a massive star and the birth of a black hole. It had a redshift of 6.3.

Redshift is a measure of the degree to which light has been "stretched" by the expansion of the Universe. The greater the redshift, the more distant the object and the earlier it is being seen in cosmic history.

Redshift 6.3 takes you 12.8 billion light-years across the Universe, to a time that is a little under a billion years after the Big Bang.

"This very high redshift burst - we may only see one of those every three years or so," Dr Gehrels told the BBC News website.

"This would be in the really early star-formation time in the Universe; and I'm very hopeful that if we can keep going for a few years, we can push that back. Once you get to redshift eight or 10, you really will be looking at the first stars."

'Alarm clock'

This is now one of the great quests in astrophysics: to tie down the timings of key events in the early Universe.

Scientists would like to see evidence of the first generation of stars. These hot, blue giants would have grown out of the cold neutral gas that pervaded the young cosmos just a few hundred million years after the Big Bang.

It is believed that when these blue stars switched on, they brought to an end a period of darkness; and also "fried" the neutral gas to produce the diffuse intergalactic plasma we detect between nearby stars today.

The caveat for Swift is that it sees stars at the ends of their lives, and there has to be a question mark over whether the redshift 8-10 era would be sufficiently mature to produce GRBs.

"For a long time, there was a worry that there was a time delay; that you needed some time to form a hypernova, perhaps up to a billion years, which meant, if correct, you wouldn't expect to see any GRBs beyond redshift 6," commented Exeter University's Dr Andy Bunker, who studies high redshift galaxies.

"Swift has now seen a redshift 6.3, which is very encouraging because it shows that any time delay is of the order of a few hundred million years rather than a billion years."

So, watch this space as Swift probes out further than any telescope has gone before.

It will still need, though, the support of other specialist observatories, operating at a range of different wavelengths, to study these far-distant locations in detail and make sense of them.

"Swift is like an 'alarm clock'," says Dr Bunker. "When it goes off, it tells you there's an interesting place to go and have look."

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