“It’s a new way to probe the universe
when it was very young.” — Zolta N Haima N
Dark matter filament illuminated
By Devin Powell
An invisible web thought to span the cosmos has now revealed one of its strands.
That thread is spun of dark matter and
connects two titanic clusters of galaxies.
Its discovery, reported July 12 in Nature,
supports the idea that galaxy clusters
grow at the intersections of dark matter
filaments, and its heft backs the claim
that such filaments hide more than half
of all matter.
As the name suggests, dark matter is
difficult to detect because it gives off no
detectable radiation. The material’s presence is typically inferred by observing its
gravitational pull on stars and galaxies.
But dark matter’s gravity also warps
spacetime and bends light passing
nearby, so that more distant galaxies
beyond the intervening dark matter
appear distorted.
Contour lines trace an invisible dark
matter filament connecting the galaxy
clusters abell 222 (bottom) and abell
223 (top) in the night sky.
only about 9 percent of that mass. Dark
matter seems to make up the rest.
“In the future I expect we will extend
this and see more of these filaments,”
says Meghan Gray, an astronomer at the
University of Nottingham in England
who wasn’t involved in the study.
Nature , suggests that a stellar
signature exists in the form of fluctuat-
ing radio waves, oscillations produced
when young stars and galaxies warm and
excite surrounding hydrogen gas. Simu-
lated when the universe was 180 million
years old, the stars and galaxies are dis-
tributed in a distinct, detectable pattern.
Eli Visbal, a graduate student at
Harvard University, and his colleagues
simulated a cube of space measuring 1. 3
billion light-years across. They filled it
with hydrogen gas and dark matter, the
invisible counterpart to normal matter,
and accounted for the recent observation
that the two kinds of matter travel at different speeds. These different rates, when
combined with varying densities of each
substance, affect star formation by stunting growth in some places and promoting
Early stars made
sight yet unseen
Signature could someday be
detected by radio telescopes
By Nadia Drake
A 3-D simulation of the early universe
suggests that the first stars left a cosmic
signature large enough to be read by
radio telescopes.
“It’s a new way to probe the universe
when it was very young,” says Zoltan
Haiman, a cosmologist at Columbia Uni-
versity, who was not involved in the new
work. “We have very few ways to do that.”
Studying early star formation is chal-
lenging because the first
galaxies were so small and,
because of the universe’s
expansion, are now exceed-
ingly distant.
But the new simulation,
described online June 20 in
a computer simulation of
the early universe depicts
regions of intense star
formation (red) separated
by voids (blue). Radio telescopes might be able to
detect a similar pattern.
it in others. “The dark matter collapses
into clumps,” Visbal says. “And the gas,
due to the force of gravity, falls into these
clumps and forms stars and galaxies.”
But not where the gas is moving too
quickly relative to the dark matter
clumps, which then have to tug harder
to get the gas to come inside. A paucity of
gas produces a star-forming void, while
dense gas congeals to form clusters of
stars and galaxies. Those clusters then
heat up and excite the surrounding sea
of neutral hydrogen atoms, which emit
radiation detectable by radio telescopes.
But such telescopes would have to scan
the sky at a frequency lower than the band
typically used by today’s most powerful radio detectors. Future instruments,
such as the enormous Square Kilometer
Array now under development on two
continents, could do the job. Another
option, says UCLA astrophysicist Steven
Furlanetto, would be a proposed project
called the Dark Ages Radio Explorer, a
lunar satellite that would use the moon as
a shield against interference from technologies like television and radio.
www.sciencenews.org
August 11, 2012 | SCIENCE NEWS | 9
