Trent Perrotto
Headquarters, Washington
202-358-5241
trent.j.perrotto@nasa.gov
Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-4673
whitney.clavin@jpl.nasa.gov
RELEASE: 11-155
NASA'S GALAXY EVOLUTION EXPLORER FINDS DARK ENERGY REPULSIVE
WASHINGTON -- A five-year survey of 200,000 galaxies, stretching back
seven billion years in cosmic time, has led to one of the best
independent confirmations that dark energy is driving our universe
apart at accelerating speeds.
The survey used data from NASA's space-based Galaxy Evolution Explorer
and the Anglo-Australian Telescope on Siding Spring Mountain in
Australia.
The findings offer new support for the favored theory of how dark
energy works - as a constant force, uniformly affecting the universe
and propelling its runaway expansion. They contradict an alternate
theory, where gravity, not dark energy, is the force pushing space
apart. According to this alternate theory, with which the new survey
results are not consistent, Albert Einstein's concept of gravity is
wrong, and gravity becomes repulsive instead of attractive when
acting at great distances.
"The action of dark energy is as if you threw a ball up in the air,
and it kept speeding upward into the sky faster and faster," said
Chris Blake of the Swinburne University of Technology in Melbourne,
Australia. Blake is lead author of two papers describing the results
that appeared in recent issues of the Monthly Notices of the Royal
Astronomical Society. "The results tell us that dark energy is a
cosmological constant, as Einstein proposed. If gravity were the
culprit, then we wouldn't be seeing these constant effects of dark
energy throughout time."
Dark energy is thought to dominate our universe, making up about 74
percent of it. Dark matter, a slightly less mysterious substance,
accounts for 22 percent. So-called normal matter, anything with
atoms, or the stuff that makes up living creatures, planets and
stars, is only approximately four percent of the cosmos.
The idea of dark energy was proposed during the previous decade, based
on studies of distant exploding stars called supernovae. Supernovae
emit constant, measurable light, making them so-called "standard
candles," which allows calculation of their distance from Earth.
Observations revealed dark energy was flinging the objects out at
accelerating speeds.
The new survey provides two separate methods for independently
checking these results. This is the first time astronomers performed
these checks across the whole cosmic timespan dominated by dark
energy. Astronomers began by assembling the largest three-dimensional
map of galaxies in the distant universe, spotted by the Galaxy
Evolution Explorer.
"The Galaxy Evolution Explorer helped identify bright, young galaxies,
which are ideal for this type of study," said Christopher Martin,
principal investigator for the mission at the California Institute of
Technology in Pasadena. "It provided the scaffolding for this
enormous 3-D map."
The team acquired detailed information about the light for each galaxy
using the Anglo-Australian Telescope and studied the pattern of
distance between them. Sound waves from the very early universe left
imprints in the patterns of galaxies, causing pairs of galaxies to be
separated by approximately 500 million light-years.
Blake and his colleagues used this "standard ruler" to determine the
distance from the galaxy pairs to Earth. As with the supernovae
studies, this distance data was combined with information about the
speeds the pairs are moving away from us, revealing, yet again, the
fabric of space is stretching apart faster and faster.
The team also used the galaxy map to study how clusters of galaxies
grow over time like cities, eventually containing many thousands of
galaxies. The clusters attract new galaxies through gravity, but dark
energy tugs the clusters apart. It slows down the process, allowing
scientists to measure dark energy's repulsive force.
"Observations by astronomers over the last 15 years have produced one
of the most startling discoveries in physical science; the expansion
of the universe, triggered by the big bang, is speeding up," said Jon
Morse, astrophysics division director at NASA Headquarters in
Washington. "Using entirely independent methods, data from the Galaxy
Evolution Explorer have helped increase our confidence in the
existence of dark energy."
For more information about NASA's Galaxy Evolution Explorer, visit:
-end-
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