'Dark Stars' Dotted Early Universe

Dec. 5, 2007 -- The earliest stars in the universe may have been cool expanses of helium and hydrogen, thick with dark matter and spitting with antimatter. There even may be a few still around.

What some astrophysicists are calling "dark stars" would have been dominated by dark matter and could have existed for millennia in the early universe, when dark matter was far more concentrated than today. Some dark stars might have even survived to the present day.

What's more, these theoretical dark matter stars may be the secret behind the giant black holes called quasars, which appear to have come into existence before galaxies had a chance to create them. That timing has that has never made much sense before.

The dark matter in these weird stars would have to be some kind of heavy subatomic particle that only interacts with normal matter by tugging on it with its gravity. Such a substance is currently the most favored hypothesis for the nature of dark matter in the universe.

"The idea that the first stars could be this type is entirely new," said astrophysicist Paolo Gondolo of the University of Utah. He and his colleagues are publishing their dark star theory in next month's issue of the journal Physical Review Letters.

Without much dark matter, stars form when a cloud of interstellar hydrogen and helium gradually cool down, contracting into a smaller and smaller space until it collapses into a hot ball of matter that can ignite nuclear fusion and become a star.

If there's too much dark matter around, as there would have been in the early universe, that scenario might not work, said Gondolo. The thicket of dark matter in the clouds of gas would cause some dark matter particles to annihilate each other, which would possibly emit antimatter electrons (positrons), gamma rays and heat.