The first
stars to form in the universe may not have shone like those today, but instead
may have been invisible "dark stars" powered by the annihilation of dark matter,
a new study finds.
And,
researchers say, they would have been gargantuan.
Dark
matter, invisible stuff which scientists think makes up the bulk of the
universe, has been considered to have role in the evolution of the early
universe but not in the formation of the first stars.
Exotic
processes
According
to the conventional theory for how the first stars were born, hydrogen and
helium atoms clumped and swirled together in proto-stellar clouds, and as they cooled,
the gas clouds shrank and became denser. The cooling and shrinking continued
until hydrogen and helium began to fuse, igniting the fusion engine that powers
our sun and other stars.
For the new
study, detailed in the January issue of the journal Physical Review Letters,
astrophysicists calculated how dark matter would have affected the temperature
and density of the gas that clumped together to form the first stars.
The
findings suggest that dark
matter particles interacted so that they "annihilated" each
other, producing subatomic particles called quarks and their antimatter
counterparts, antiquarks. This annihilation produced heat that would have kept
the proto-stellar cloud of hydrogen and helium from cooling and shrinking and
thus preventing fusion reactions from igniting.
"The
heating can counteract the cooling, and so the star stops contracting for a
while, forming a dark star" some 80 million to 100 million years after the
Big Bang, said study team member Paolo Gondolo of the University of Utah.
Large
and fluffy
These
so-called dark stars, named for the song "Dark Star" by the Grateful
Dead, would contain mostly normal matter, in the form of hydrogen and helium
molecules, but would be vastly larger (about 400 to 200,000 times wider) and
"fluffier" than the sun and other stars.
It is
conceivable that dark stars exist today, though they would not emit visible
light. Instead they would produce gamma rays, neutrinos and antimatter
such as positrons and antiprotons, Gondolo said.
"With
your bare eyes, you can't see a dark star," Gondolo said, "but the
radiation would fry you."
The
findings of the study have opened a new phase in the evolution of stars and
could aid in the search to find and identify exactly what dark matter is,
Gondolo added.
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