Page last updated at 19:07 GMT, Thursday, 12 February 2009

Simulation targets early cosmos

By Jonathan Amos
Science reporter, BBC News

Redshift 8.5 simulation (A.Orsi/ICC-Durham)
In the model, green swirls represent dark matter, circles indicate the star formation rate in galaxies

Scientists have used a supercomputer to simulate what the Universe was like as the first galaxies were forming.

The model maps how matter is thought to have been distributed a few hundred million years after the Big Bang.

The work should help astronomers hunt down ancient galaxies using the latest telescope technologies - they will know what to look for.

The simulation has been produced by scientists at Durham University's Institute of Computational Cosmology.

"The calculation we've done has predictions for what we should see in a few years' time when the massive telescopes in the Southern Hemisphere are fitted with new instrumentation - cameras and detectors - to observe early epochs, stretching right back to when the Universe was less than a tenth of its present age," said Durham researcher Dr Carlton Baugh.

Reaching back

Current estimates have the Universe coming into being 13.7 billion years ago, but the conditions suitable to make the first stars would not have existed for many tens of millions of years after that event; and the first groupings - or galaxies - of stars would have formed even nearer in time.

Astronomers are keen to tie down the timings of these key events because they will help them understand how the cosmos evolved to look the way it does now.

Their problem is that the light reaching Earth from these early epochs is incredibly faint and present telescope technology is at its limits in terms of being able to detect the most ancient and distant objects.

The Durham simulation provides in effect a "photofit" that astronomers can work off as they scan deep into space.

It predicts where the galaxies should appear, how they ought to grow and how vigorously they should have produced their stars. The simulation runs forward right to the present day.

Cosmic 'recipe'

The team hopes its modelling work can give some insights into the nature of "dark matter" - a mysterious substance that accounts for most of the mass in the cosmos but which neither reflects nor emits any detectable light.

It does, though, gravitationally pull on normal matter (the gas, stars, and planets we see in space) and is regarded as an essential ingredient in galaxy formation.

The Durham simulation reveals how structures develop in a Universe filled with dark matter.

"We're trying to model the physics of galaxy formation with dark matter providing the gravity to suck the gas together," explained Dr Baugh.

"It's massive trial and error. You try different 'recipes' for the physics, you then run the calculations and see what they look like; and if they look like the real Universe, you stop. But more often than not, they don't, so you have to keep experimenting and varying the recipe," he told BBC News.

New telescope

Theory suggests early activity in the Universe would have been dominated by giant hot stars. They would likely have burned brilliant but brief lives, producing the first heavy elements.

Their radiation would also have "fried" the cold neutral gas around them to produce the diffuse intergalactic plasma we detect between nearby stars today.

But this theory demands the earliest star-forming phase in the Universe was also a busy one, and future observations will want to see evidence of galaxies that produce stars at sufficient rates.

"Our type of calculations help design experiments; it's not just theoretical interest," said Dr Baugh.

"We've looked at the instrumentation that they're now building into telescopes and we think they should be surveying larger patches of sky."

The UK's newest telescope will be able to do just that. The Vista facility being built in Chile will use a four-metre mirror to undertake wide-field studies. It will have an instrument known as Elvis (Emission-Line galaxies with VISTA Survey) to track down ancient galaxies.

The Durham research has been published in the Monthly Notices of the Royal Astronomical Society. Its lead author is Dr Alvaro Orsi.

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