The earliest stars of the Universe may be much older than previously thought following the discovery of the strongest evidence for an entirely new kind of galaxy by scientists using CSIRO's Australia Telescope and the Hubble Space Telescope.
"We think they are galaxies that are absolutely fizzing with star formation - a sort of huge stellar baby-boom," says CSIRO's Professor Ray Norris, leader of the Australia Telescope observing team.
"They seem to be a hundred times more active than even the most frenzied star-forming galaxy in today's Universe - the kind of galaxy we call 'starburst'," he says.
Many of these galaxies must be very faint. They might be very common, even outnumbering all the distant galaxies that astronomers had seen before.
"If that's the case, it pushes back the epoch of maximum star formation - when the Universe really got active - by a long way," Professor Norris says.
"The Australia Telescope observations have unearthed a source that may be a key to understanding how galaxies began to form," says Dr Bob Williams, the former Director of the Space Telescope Science Institute who initiated the Hubble Deep Field observing campaigns.
"If the strange source the Australia Telescope has found is an early starburst galaxy, then we now have solid evidence for what may have been a brief and furious burst of star formation activity in some unique galaxies - possibly the first really large structures that formed in the universe," he says.
"For astronomers, this is like pushing back the date at which people arrived in Australia, or the date at which life started on Earth," comments Dr Brian Boyle, Director of the Anglo-Australian Observatory, which helped to select the region of sky to be observed.
Professor Norris says that because light takes a finite time to travel, 'far away' in space equals 'long ago'. When looking deep into space astronomers are looking back into the history of the Universe and seeing galaxies that no longer exist.
The Hubble Space Telescope (HST) made its first deep scrutiny of the Universe in 1993. In a tiny patch of the northern sky it picked out galaxies that existed when the Universe was only a tenth of its present age.
In 1998 the HST's keen eye was turned on a patch of the southern sky, called the Hubble Deep Field South. The exact patch to be viewed was determined joint observations by the Anglo-Australian Telescope, Australia's largest optical telescope, and CSIRO's Australia Telescope, the most advanced radio telescope in the Southern Hemisphere. The HST and the Australia Telescope then examined the area in detail.
The radio telescope observations show that a faint red dot in the Hubble field, dubbed 'source c', is a very unusual object.
The colours of its light suggest that it lies between five and eleven billion light-years away.
"That in itself is not remarkable," says Professor Norris. "But this galaxy is the most extreme example of a class of objects in the Hubble fields which are very faint in visible light but quite bright at radio wavelengths".
For now, astronomers are stuck with a mystery. But the next generation of telescopes will help them clear up the tantalizing questions so far raised about the early Universe, says Dr Norris.
"Even the world's largest telescope, the Very Large Telescope in Chile, can't collect enough light from this object to really pin down its distance. That will probably have to wait for optical telescopes now on the drawing board - ones with mirrors 30 m across or even bigger."
The first of these giant light buckets, the California Extremely Large Telescope, may be built in the next few years.
Astronomers are also looking forward to a 'mega-collector' radio telescope, the Square Kilometre Array, due for construction around 2010. This may be built in Australia.
"The Square Kilometre Array will be able to detect galaxies like 'source c' at great distances. It could tell us just how common these objects are in the early Universe," says Professor Norris.
Images available at: http://www.csiro.au/page.asp?type=mediaRelease&id=rayuniverse
The above story is based on materials provided by CSIRO Australia. Note: Materials may be edited for content and length.
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