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Science Forum Index » Astro - Amateur Forum » Filling the Gap in Stellar History...
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| Sam Wormley... |
 Posted: Mon Aug 04, 2008 11:41 pm |
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Filling the Gap in Stellar History
http://sciencenow.sciencemag.org/cgi/content/full/2008/731/2
By Phil Berardelli
ScienceNOW Daily News
31 July 2008
We may never know for sure what the first stars in the universe looked like, but a new
computer simulation has provided researchers with some initial brush strokes. In
tomorrow's issue of Science, an international team reports that they have simulated the
birth of a protostar--a nugget that could grow eventually into a supermassive
star--starting with the basic ingredients and conditions that existed in the early universe.
Cosmologists probably know more about the first few minutes after the big bang--thought to
have occurred about 13.7 billion years ago--than they do about the following billion years
of the universe's existence, sometimes known as the cosmic dark ages. Within that interim,
the first stars formed and began to light up the universe.
The problem with studying those very early stars is that they no longer exist. According
to theory, all or nearly all of them began as supergiants hundreds of times more massive
than the sun. Then they expended their nuclear fuel and exploded within a few million
years. This early demise was good for the evolution of the universe, because the
supergiants dispersed the heavy elements necessary to form smaller stars as well as
planets and, eventually, people. But unfortunately for scientists, the primordial beasts
also expunged all detectable evidence of themselves.
A team led by physicist Naoki Yoshida of Nagoya University in Japan set out to fill this
cosmic evolutionary gap in the only way currently possible: They carried out a computer
simulation that duplicates the process of star formation in the very young universe. The
task actually proved easier than it would have been to simulate stellar evolution in the
present day. That's because the current galactic environment is full of magnetic fields
and turbulence, both of which greatly complicate the creation of accurate simulations. Not
so in the first few million years after the big bang. Back then, all stars needed to form
was a primordial soup of mostly hydrogen and some helium atoms, perturbed by the effects
of gravity on minuscule differences in the density of the gases, and the mysterious
substance known as dark matter.
Taking those elements, the researchers traced the collapse of a primordial gas cloud, from
a halo roughly 1000 light-years in diameter, to a newborn but still unignited protostar
with a radius about 25 times that of the sun. Astrophysicist and co-author Lars Eric
Hernquist of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts,
says that a protostar could grow quickly, accreting about 10 solar masses within 1000
years, and reaching its full size of 100 or more times the sun's mass in as little as
10,000 years. That's fast enough to crowd the young universe with supergiants whose
explosions would provide the materials for future stars and galaxies. But it's still
difficult to determine how many primordial stars there were, Hernquist says.
The simulation shows the creation of the first protostars in "great detail and physical
realism," says astrophysicist Volker Bromm of the University of Texas, Austin. It "puts
the finishing touches to the decade-old quest to build the first star from first
principles," he says. But Bromm adds that the investigation needs to be carried forward to
see how the primordial stars continued to evolve. It's possible, he says, that there might
be some unforeseen process at work that could change current understanding of early star
formation. |
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