For years,
astronomers have thought that the first stars born in the universe formed
alone, but new simulation results suggest that some of them may have had
partners.
The first
stars began as cold clumps of hydrogen and helium gas that started to
coalesce into stellar embryos. Many of them were huge, astronomers think. Telescopes
can't yet peer back far enough in time to see this first generation of stars,
but computer simulations can model their formation and tell astronomers what
they might have looked like.
These
simulations indicated that these earliest stars would have been whoppers,
with masses hundreds of times that of our sun, and would likely have formed in
single-star systems.
"While
binaries had been proposed, they'd never been seen in cosmological
simulations," said Matthew Turk, a graduate student at Stanford University who ran the new simulations.
Binary and
even triple
star systems are common in the more modern universe, and they are typically
much less massive than early-generation stars.
In the new
simulations, Turk and his colleagues Tom Abel, also of Stanford, and Brian
O'Shea of Michigan State University included more precise information to
better mimic the conditions thought to have existed in the early universe.
When they
ran the simulation, they got what Turk called a "rather surprising
result": They saw indications of fragmentation in the gas clouds that
suggested the formation of a binary star system.
"When
we started the simulation, we didn't know it was going to form a binary,"
Turk told SPACE.com.
Just how
many early stars might have been binaries isn't clear yet determining their
abundance will take many more simulations.
"The
idea here is that it's not forbidden, that it seems like [the stars] form
alone, but sometimes they might have some friends, they might form in
pairs," Turk said.
The
finding, detailed in the July 10 issue of the journal Science, also
jibes with observations of very old, low mass stars in the halo of the Milky
Way, O'Shea said.
Mass
mismatch
These early
stars and galaxies later merged to form today's galaxies [, such as our own
Milky Way. By observing them and analyzing their compositions, astronomers
can estimate the average masses of the earliest stars, O'Shea explained.
The
estimates from this method suggested that the first stars weren't quite as
massive as expected, with the average falling around 30 to 40 solar masses.
The new
simulations explain the discrepancy between the massive stars seen in
simulations and the estimates of much smaller masses: "Instead of one big
star, you get two smaller stars," O'Shea told SPACE.com.
The finding
that early stars might have been binaries could have implications for the
detection of gamma ray bursts in the early universe.
Gamma
rays and gravity waves
These
energetic explosions are thought to occur when a massive star rotates very fast
and then collapses. The doomed stars are spun up by companion stars that strip
off their partner's outer layers.
Having
binaries in the early universe suggests that gamma ray bursts also occurred
early on. When NASA's James Webb Telescope is launched into spacein 2013, it
will be able to peer further back into the universe's past than any other
telescope, and should be able to see the supernovas that go along with the
gamma ray bursts, O'Shea said.
The
existence of early binaries could also have implications for the detection of
elusive gravity
waves, disturbances predicted by general relativity.
Gravity
waves from single black holes are difficult to detect above normal noise to
pick up the signal assuming any exist astronomers need a dynamic, evolving
system, which is just what a pair of black holes would provide.
The team
plans to do more simulations to get a better picture of just how common binary
star systems might have been in the early universe and what the likely masses
of these stars might have been.
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