NASA News: 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:

http://www.nasa.gov/galex

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Free-Floating Planets May Be More Common Than Stars

WASHINGTON -- Astronomers, including a NASA-funded team member, have
discovered a new class of Jupiter-sized planets floating alone in the
dark of space, away from the light of a star. The team believes these
lone worlds probably were ejected from developing planetary systems.

The discovery is based on a joint Japan-New Zealand survey that
scanned the center of the Milky Way galaxy during 2006 and 2007,
revealing evidence for up to 10 free-floating planets roughly the
mass of Jupiter. The isolated orbs, also known as orphan planets, are
difficult to spot, and had gone undetected until now. The planets are
located at an average approximate distance of 10,000 to 20,000 light
years from Earth.

"Although free-floating planets have been predicted, they finally have
been detected, holding major implications for planetary formation and
evolution models," said Mario Perez, exoplanet program scientist at
NASA Headquarters in Washington.

The discovery indicates there are many more free-floating Jupiter-mass
planets that can't be seen. The team estimates there are about twice
as many of them as stars. In addition, these worlds are thought to be
at least as common as planets that orbit stars. This adds up to
hundreds of billions of lone planets in our Milky Way galaxy alone.

"Our survey is like a population census," said David Bennett, a NASA
and National Science Foundation-funded co-author of the study from
the University of Notre Dame in South Bend, Ind. "We sampled a
portion of the galaxy, and based on these data, can estimate overall
numbers in the galaxy."

The study, led by Takahiro Sumi from Osaka University in Japan,
appears in the May 19 issue of the journal Nature.
The survey is not sensitive to planets smaller than Jupiter and
Saturn, but theories suggest lower-mass planets like Earth should be
ejected from their stars more often. As a result, they are thought to
be more common than free-floating Jupiters.

Previous observations spotted a handful of free-floating planet-like
objects within star-forming clusters, with masses three times that of
Jupiter. But scientists suspect the gaseous bodies form more like
stars than planets. These small, dim orbs, called brown dwarfs, grow
from collapsing balls of gas and dust, but lack the mass to ignite
their nuclear fuel and shine with starlight. It is thought the
smallest brown dwarfs are approximately the size of large planets.

On the other hand, it is likely that some planets are ejected from
their early, turbulent solar systems, due to close gravitational
encounters with other planets or stars. Without a star to circle,
these planets would move through the galaxy as our sun and others
stars do, in stable orbits around the galaxy's center. The discovery
of 10 free-floating Jupiters supports the ejection scenario, though
it's possible both mechanisms are at play.

"If free-floating planets formed like stars, then we would have
expected to see only one or two of them in our survey instead of 10,"
Bennett said. "Our results suggest that planetary systems often
become unstable, with planets being kicked out from their places of birth."

The observations cannot rule out the possibility that some of these
planets may have very distant orbits around stars, but other research
indicates Jupiter-mass planets in such distant orbits are rare.

The survey, the Microlensing Observations in Astrophysics (MOA), is
named in part after a giant wingless, extinct bird family from New
Zealand called the moa. A 5.9-foot (1.8-meter) telescope at Mount
John University Observatory in New Zealand is used to regularly scan
the copious stars at the center of our galaxy for gravitational
microlensing events. These occur when something, such as a star or
planet, passes in front of another more distant star. The passing
body's gravity warps the light of the background star, causing it to
magnify and brighten. Heftier passing bodies, like massive stars,
will warp the light of the background star to a greater extent,
resulting in brightening events that can last weeks. Small
planet-size bodies will cause less of a distortion, and brighten a
star for only a few days or less.

A second microlensing survey group, the Optical Gravitational Lensing
Experiment (OGLE), contributed to this discovery using a 4.2-foot
(1.3 meter) telescope in Chile. The OGLE group also observed many of
the same events, and their observations independently confirmed the
analysis of the MOA group.

For more information about NASA's exoplanet research, visit:

http://planetquest.jpl.nasa.gov/

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