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Tuesday, August 22, 2006

NASA Finds Direct Proof of Dark Matter

X-ray/Optical Composite of 1E 0657-56
X-ray/Optical Composite of 1E 0657-56

Press Image and Caption




Dark matter and normal matter have been wrenched apart by the tremendous collision of two large clusters of galaxies.
The discovery, using NASA's Chandra X-ray Observatory and other
telescopes, gives direct evidence for the existence of dark matter.


"This is the most energetic cosmic event, besides the Big Bang, which
we know about," said team member Maxim Markevitch of the
Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.


___continued...click link below >>>


CONTINUED...








Lensing Illustration
Gravitational Lensing Explanation

These observations provide the strongest evidence yet that most of the
matter in the universe is dark. Despite considerable evidence for dark
matter, some scientists have proposed alternative theories for gravity
where it is stronger on intergalactic scales than predicted by Newton
and Einstein, removing the need for dark matter. However, such theories
cannot explain the observed effects of this collision.


"A universe that's dominated by dark stuff seems preposterous, so we
wanted to test whether there were any basic flaws in our thinking,"
said Doug Clowe of the University of Arizona at Tucson, and leader of
the study. "These results are direct proof that dark matter exists."










Animation of Cluster Collision
Animation of Cluster Collision

In galaxy clusters, the normal matter, like the atoms that make up the
stars, planets, and everything on Earth, is primarily in the form of
hot gas and stars. The mass of the hot gas between the galaxies is far
greater than the mass of the stars in all of the galaxies. This normal
matter is bound in the cluster by the gravity of an even greater mass
of dark matter. Without dark matter, which is invisible and can only be
detected through its gravity, the fast-moving galaxies and the hot gas
would quickly fly apart.


The team was granted more than 100 hours on the Chandra telescope to
observe the galaxy cluster 1E0657-56. The cluster is also known as the
bullet cluster, because it contains a spectacular bullet-shaped cloud
of hundred-million-degree gas. The X-ray image shows the bullet shape
is due to a wind produced by the high-speed collision of a smaller
cluster with a larger one.










4-Panel Illustrations of Cluster Collision
4-Panel Illustrations of Cluster Collision

In addition to the Chandra observation, the Hubble Space Telescope, the
European Southern Observatory's Very Large Telescope and the Magellan
optical telescopes were used to determine the location of the mass in
the clusters. This was done by measuring the effect of gravitational
lensing, where gravity from the clusters distorts light from background
galaxies as predicted by Einstein's theory of general relativity.


The hot gas in this collision was slowed by a drag force, similar to
air resistance. In contrast, the dark matter was not slowed by the
impact, because it does not interact directly with itself or the gas
except through gravity. This produced the separation of the dark and
normal matter seen in the data. If hot gas was the most massive
component in the clusters, as proposed by alternative gravity theories,
such a separation would not have been seen. Instead, dark matter is
required.










Galaxy Cluster in Perspective
Animation: Galaxy Cluster in Perspective

"This is the type of result that future theories will have to take into
account," said Sean Carroll, a cosmologist at the University of
Chicago, who was not involved with the study. "As we move forward to
understand the true nature of dark matter, this new result will be
impossible to ignore."


This result also gives scientists more confidence that the Newtonian
gravity familiar on Earth and in the solar system also works on the
huge scales of galaxy clusters.



"We've closed this loophole about gravity, and we've come closer than ever to seeing this invisible matter," Clowe said.




These results are being published in an upcoming issue of The
Astrophysical Journal Letters. NASA's Marshall Space Flight Center,
Huntsville, Ala., manages the Chandra program for the agency's Science
Mission Directorate. The Smithsonian Astrophysical Observatory controls
science and flight operations from the Chandra X-ray Center, Cambridge,
Mass.



Additional information and images can be found at:




http://chandra.harvard.edu

and

http://chandra.nasa.gov











1E 0657-56
Credit:
X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optical: NASA/STScI;
Magellan/U.Arizona/D.Clowe et al.; Lensing Map: NASA/STScI; ESO WFI;
Magellan/U.Arizona/D.Clowe et al.
JPEG (479 kb)Tiff (9.2 MB)PS (2.8 MB)






This composite image shows the galaxy cluster 1E 0657-56, also known as the
"bullet cluster."
This cluster was formed after the collision of two large
clusters of galaxies, the most energetic event known in the universe since
the Big Bang.










Lensing Illustration
Gravitational Lensing Explanation


Hot gas detected by Chandra in X-rays is seen as two pink clumps in the
image and contains most of the "normal," or baryonic, matter in the two
clusters. The bullet-shaped clump on the right is the hot gas from one
cluster, which passed through the hot gas from the other larger cluster
during the collision. An optical image from Magellan and the Hubble Space
Telescope shows the galaxies in orange and white. The blue areas in this
image show where astronomers find most of the mass in the clusters. The
concentration of mass is determined using the effect of so-called
gravitational lensing, where light from the distant objects is distorted by
intervening matter. Most of the matter in the clusters (blue) is clearly
separate from the normal matter (pink), giving direct evidence that nearly
all of the matter in the clusters is dark.










Animation of Cluster Collision
Animation of Cluster Collision


The hot gas in each cluster was slowed by a drag force, similar to air
resistance, during the collision. In contrast, the dark matter was not
slowed by the impact because it does not interact directly with itself or
the gas except through gravity. Therefore, during the collision the dark
matter clumps from the two clusters moved ahead of the hot gas, producing
the separation of the dark and normal matter seen in the image. If hot gas
was the most massive component in the clusters, as proposed by alternative
theories of gravity, such an effect would not be seen. Instead, this
result shows that dark matter is required.

































































Fast Facts for 1E 0657-56:
Credit X-ray: NASA/CXC/CfA/M.Markevitch et al.;
Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.; Lensing Map:
NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al.
Scale Image is 7.5 x 5.4 arcmin
Category Groups & Clusters of Galaxies
Coordinates (J2000) RA 06h 58m 19.85s | Dec -55' 56" 29.40ยบ
Constellation Carina
Observation Dates 
2004: Aug 10, 11, 14, 15, 17, 19, 24, 25

Observation Time 140 hours
Obs. IDs 
5355-58, 5361, 4984-86

Color Code Energy (X-ray: Pink; Optical: White/Orange; Lensing Map: Blue)
Instrument ACIS
Also Known As The Bullet Cluster
Distance Estimate About 3.4 billion light years
Release Date August 21, 2006




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