From: Reuters
Published September 14, 2007 07:14 AM

Dark matter key to formation of first stars

LONDON (Reuters) - Dark matter may have played a key role in forming the earliest stars, according to researchers who suggest that the mysterious and invisible material may also have been responsible for creating black holes.



Their experiment offer clues to the universe just after the big bang some 13 billion years ago and indicates that dark matter helped set the thermostat on the first stars, said Tom Theuns, an astronomer at Durham University, who led the study published in the journal Science on Thursday.



"What is new is we were first to show the properties of these first stars depended so crucially on dark matter," Theuns said in a telephone interview. "If the dark matter is warm, some of these primordial stars should be lurking in our galaxy."


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Most physicists believe that dark matter, whose presence is known only due to its gravitational impact on celestial objects, makes up about 90 percent of all matter in the universe. Normal matter, which is everything we can see and feel, makes up the rest.



As the universe initially was only helium and hydrogen, dark matter was critical in providing the gravitational force to pull these elements together to form stars. Now that there are other objects in the galaxy, dark matter is not needed to form stars.



"Stars today form in giant clouds of molecular gas and dust embedded in the disks of large galaxies like our Milky Way, whereas the first stars emerged inside 'minihalos', agglomerates of primordial gas and dark matter with a total mass of a million times that of the Sun," Volker Bromm of the University of Texas wrote in a commentary.



ONE STAR AT A TIME



Running computer simulations, the team found slow-moving, cold dark matter particles would have created one star at a time in isolation -- generally a massive and relatively short-lived body at least 100 times the size of the sun.



In contrast, faster-moving warm dark matter would have created a large number of stars of all sizes in huge cosmic bursts that occurred in long , thin filaments of condensed gases. The researchers do not know which scenario played out but said that either way, dark matter was key.



Stars formed in cold dark matter would be long gone but smaller, slower-burning ones formed from warm dark matter could still be shining in the Milky Way, Theuns said.



And because stars produce heavy elements like carbon, oxygen and silicon, it is possible that materials embedded in the Sun and Earth came from these ancient bodies, Theuns said.



"The first stars were the first producers of these elements, so some of them ended up in the Sun, the Earth and us," he said. "These elements are necessary for life as we know it."



The computer models also provided insight into the role warm dark matter plays in the creation of black holes, objects in space so massive they pull most matter in, leaving even light unable to escape.



Scientists believe most galaxies have black holes in their centers but are unsure how exactly they got there. Perhaps stars formed from warm dark mater collided with each other to create the black holes, Theuns said.



"We suggest the collision of the stars leads to the formation of black holes, which eat even more stars and grow as it gets bigger," he said.


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