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How the First Stars Were Born

July 31, 2008

A
new supercomputer simulation offers the most detailed view yet of how the first
stars evolved after the Big Bang.

The
model follows the simpler physics that ruled the early universe to see how cold
clumps of gas eventually grew into giant star embryos.

“Until
you put that physics in the code, you can’t evaluate how the first protostars
formed,” said Lars Hernquist, an astrophysicist at Harvard University whose early-stars model is detailed in this week’s issue of the journal Science.
His remarks were made Wednesday during a press teleconference.

Mysterious “dark
matter”
provided the first gravitational impetus for hydrogen and
helium gas to start clumping together, Hernquist said. The gas began releasing
energy as it condensed, forming molecules from atoms, which further cooled the
clump and allowed for even greater condensing.

Unlike
previous models, the latest simulation takes this cooling process of “complex
radiative transfer” into account, said Nagoya University astrophysicist Naoki
Yoshida, who headed up the modeling project.

Eventually
gravity could not condense the gas cloud any further, because the densely-packed
gas exerted a pressure against further collapse. That equilibrium point marked
the beginning of an embryonic star, called a protostar by astronomers.

Simulation
runs show that the first protostar likely started with just 1 percent the mass
of our sun, but would have swelled to more than 100 solar masses in 10,000
years.

“No
simulation has ever gotten to the point of identifying this important stage in
the birth
of a star
,” Hernquist noted.

The
first protostars reached such massive size because they consisted of mainly
simple elements such as hydrogen and helium. That bloated existence means the stars
which eventually form from such protostars could create heavier
elements
such as oxygen, carbon, nitrogen and iron in their fiery furnaces.

The
researchers eventually hope to run the simulation all the way up through the
point where protostars ignite
into true stars
.


Source: imaginova



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