Dwayne Brown/Tabatha Thompson
Headquarters, Washington
202-358-1726/3895
Susan Hendrix
Goddard Space Flight Center, Greenbelt, Md.
301-286-7745
Ray Villard
Space Telescope Science Institute, Baltimore
410-338-4514
RELEASE: 07-02
HUBBLE MAPS THE COSMIC WEB OF "CLUMPY" DARK MATTER IN 3-D
SEATTLE - An international team of astronomers using NASA's Hubble
Space Telescope has created the first three-dimensional map of the
large-scale distribution of dark matter in the universe.
Dark matter is an invisible form of matter whose total mass in the
universe is more than five times that of "normal" matter (i.e.,
atoms). The nature of dark matter is still unknown. Its presence in
the universe is inferred from its current influence within galaxies
and clusters of galaxies, and the gravitational effect it has had on
the evolution of structure in the universe. The first direct
detection of dark matter was made this past year through observations
of the Bullet Cluster of galaxies.
This new map provides the best evidence to date that normal matter,
largely in the form of galaxies, accumulates along the densest
concentrations of dark matter. The map reveals a loose network of
filaments that grew over time and intersect in massive structures at
the locations of clusters of galaxies.
The map stretches halfway back to the beginning of the universe and
shows how dark matter has grown increasingly "clumpy" as it collapses
under gravity.
The dark matter map was constructed by measuring the shapes of half a
million faraway galaxies. To reach Hubble, the light of the galaxies
traveled through intervening dark matter. The dark matter deflected
the light slightly as it traveled through space. Researchers used the
observed, subtle distortion of the galaxies' shapes to reconstruct
the distribution of intervening mass along Hubble's line of sight, a
method called "weak gravitational lensing."
For astronomers, the challenge of mapping dark matter in the universe
has been similar to mapping a city from nighttime aerial snapshots
showing only streetlights. Dark matter is invisible, so only the
luminous galaxies can be seen directly. These new map images are
equivalent to seeing a city, its suburbs and country roads in
daylight for the first time. Major arteries and intersections become
evident, and a variety of neighborhoods are visible.
Mapping dark matter's distribution in space and time is fundamental to
understanding how galaxies grew and clustered over billions of years.
Tracing the growth of clustering in dark matter may eventually also
shed light on dark energy, a repulsive form of gravity that would
have influenced how dark matter clumps.
The research results appeared online today in the journal Nature and
were presented at the 209th meeting of the American Astronomical
Society in Seattle, Wash., by Richard Massey and Nick Scoville. Both
researchers are from the California Institute of Technology,
Pasadena, Calif.
"It's reassuring how well our map confirms the standard theories for
structure formation," said Massey. He calls dark matter the
"scaffolding" inside of which stars and galaxies have been assembled
over billions of years.
Researchers created the map using the Hubble's largest survey to date
of the universe, the Cosmic Evolution Survey, otherwise known as
COSMOS. The survey covers an area of sky nine times the area of the
Earth's moon. This allows for the large-scale filamentary structure
of dark matter to be evident. To add 3-D distance information, the
Hubble observations were combined with multicolor data from powerful
ground-based telescopes, Europe's Very Large Telescope in Chile,
Japan's Subaru telescope in Hawaii, the U.S.'s Very Large Array radio
telescope, New Mexico, as well as the European Space Agency's
orbiting XMM-Newton X-ray telescope.
The Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency. The Space Telescope
Science Institute, Baltimore, conducts Hubble science operations. The
Institute is operated for NASA by the Association of Universities for
Research in Astronomy, Inc., Washington.
For more information and images about this research, visit:
http://hubblesite.org/news/2007/01
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