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Last Updated: Wednesday, 6 April, 2005, 18:22 GMT 19:22 UK
Astronomers expect to be 'Dazled'
By Jonathan Amos
BBC News science reporter, in Birmingham

The VLT (Eso)
The VLT facility sits on top of the Paranal Mountain in Chile
UK and Australian astronomers are about to use a new instrument to detect the most distant galaxies yet observed.

Dazle is tuned to search for specific infrared wavelengths of light that should be associated with some of the first stars to shine in the Universe.

The instrument will be fitted to the 8m Melipal Very Large Telescope at Paranal in Chile.

University of Cambridge researchers gave details of their work at the UK National Astronomy Meeting.

The researchers said they hoped to see stars that were more than 12 billion light-years away - stars which may have played a crucial role in altering the entire cosmic environment.

"These observations are very difficult and previous attempts to look back this far have so far been unsuccessful, so Dazle could be groundbreaking," said Dr Richard McMahon, from the Institute of Astronomy.

Bigger numbers

Dazle stands for Dark Age Redshift Lyman Explorer. The instrument must be cooled to -40 Celsius and will sit inside a large freezer box.

Dazle (Institute of Astronomy)
Dazle will be put inside a freezer box on the side of Melipal
The word redshift refers to the measure astronomers use to describe the way light coming from far-distant galaxies is "stretched" by the expansion of the Universe (Redshift is given the unit abbreviation of "z", hence the letter's use in the acronym Dazle).

The higher the redshift number assigned to an object, the more distant it is and the earlier it is being seen in cosmic history.

Current technologies on the best telescopes are seeing out to redshifts of six-plus. Dazle, when it analyses the light captured by the Melipal telescope, expects to start out with observations that have a redshift of 7.8.

"That takes us back 12.8 billion years and that's 650 million years after the Big Bang," Dr McMahon told the BBC News website.

Cosmic 'archaeology'

The research is part of the major drive in astronomy now 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.

"There are two ways of working in astronomy," commented Dr Andrew Bunker from Exeter University, who also studies high-redshift galaxies.

"You can either do 'archaeology': you can measure ages of stars and infer when they formed; or through the miracle of Hubble expansion and being able to look back in time, you can try to catch them in the act of being born. That's what Dazle will do."

The Dazle instrument in its current form expects to see a redshift eventually of 8.8, equivalent to a distance of 12.9 billion light years.

But, says Dr McMahon, there is every reason to believe the technique on which it depends could get out to redshifts in the region of 15, just a little under 300 million years after the Big Bang.

This will require some extra technologies, though, and these may not come until we also get the proposed new giant telescopes in the next few decades.

These facilities would have tremendous power, gathering light on mirrors that are 100m across.

The Royal Astronomical Society's National Astronomy Meeting is being held at the University of Birmingham.

Telescope catches early starlight
06 Apr 05 |  Science/Nature
Hubble's deepest shot is a puzzle
23 Sep 04 |  Science/Nature
Hubble sees the faintest galaxies
04 Jun 04 |  Science/Nature

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