Atom & Cosmos
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First stars not all so lonely
Simulations suggest cosmic partnerships
By Ron Cowen
It’s always nice to have a companion. And
in the lonely, dark expanse of the early
universe, even some of the first stars had
soul mates, new simulations reveal.
Previous work had indicated that the
first stars were extremely massive — at
least 100 times as heavy as the sun — but
were loners (SN: 6/8/2002, p. 362).
Now, more detailed modeling, including a careful consideration of how
atomic and molecular hydrogen interact at low densities, reveals that at least
5 percent and perhaps as many as half
of these heavyweights were gravitationally bound to similar-mass companions,
says Tom Abel of Stanford University.
He and his colleagues, Matthew Turk of
Stanford and Brian O’Shea of Michigan
State University in East Lansing, report
their findings online July 9 in Science.
Pairs of massive stars are intriguing,
notes Abel, because
each star will probably collapse into a
black hole. The eventual coalescence of the
adjacent black holes
would be a key source
of gravitational waves,
ripples in spacetime
predicted by general
relativity but never
A second star’s presence could also
add to its partner’s spin, and the resulting more rapid rotation would enhance
the production of gamma-ray bursts,
flashes of high-energy light that have
long-lasting afterglows and provide a
window on the early universe.
Only one in five of the team’s simulations, which model star formation about
200 million years after the Big Bang,
produced pairs. And the team can only
A simulation of a star-forming region about 200 million
years after the Big Bang shows two embryonic stars
(yellow) separated by 800 times the Earth-sun distance.
provide a rough estimate of the percentage of partnered stars.
“The simulations make good sense,”
says theorist Volker Bromm of the University of Texas at Austin. Bromm says
that his own team’s simulations track the
evolution of pairs further, long enough
to see the stars mature, and suggest that
the fledgling stars remain close partners.
His team plans to post a paper online
describing the results.
Study sizes up
Small, old black hole places
new limit on hidden spaces
If the gravitational force leaks out along
an extra dimension, as some versions of
string theory suggest, it would be weaker
in the observable 3-D space.
In basic string theory, which describes
subatomic particles as tiny vibrating
loops or strands of energy, extra dimensions are too small to be directly detected.
But some versions of string theory allow
larger extra dimensions, detectable by
measuring the force of gravity at small
distances or from the results of atom-smasher experiments or astrophysical
observations (SN: 2/19/2000, p. 122).
“The existence of large extra dimensions seems like an attractive idea in
theoretical physics, but they have not
revealed themselves in any experiment
so far,” Gnedin notes.
Enter small, old black holes. All black
holes radiate energy, known as Hawking
radiation. As it radiates, the black hole
By Ron Cowen
The size of any hidden extra dimension beyond the familiar three must be
less than 3 micrometers, a new analysis
based on an old black hole has found.
That new size limit is less than half
that of previous such limits, Oleg Gnedin
of the University of Michigan in Ann
Arbor and his colleagues report in a study
posted online June 30 at arXiv.org.
Dimensions beyond the common
three of space and one of time might
explain why the strong nuclear force is
roughly 1040 times stronger than gravity.
7 | SCIENCE NEWS | August 1, 2009
shrinks, and the shrinking proceeds more
rapidly as the black hole gets smaller. In
some models, extra dimensions dramatically speed up that rate, hastening the
black hole’s demise, notes theorist Igor
Klebanov of Princeton University. The
larger the extra dimension, the faster the
black hole evaporates.
Two years ago, astronomers reported
evidence for a black hole, only about
10 times as heavy as the sun, in the galaxy
NGC 4472, some 50 million light-years
from Earth. The cluster containing the
black hole is about 10 billion years old,
researchers say. The very existence of
a black hole this small and old suggests
that any extra dimension cannot exceed
3 micrometers, the team calculates.
But Paul Steinhardt of Princeton University cautions that the details of the new
limit depend on exactly which model for
extra dimensions scientists rely on.