NASA discovers new evidence of dark matter

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Monday, August 21, 2006

New observations of the distribution of mass show clear evidence of the separation of dark matter and normal matter, according to NASA scientists.

The Bullet Cluster, 4 billion light years away from Earth, is formed by two galactic clusters colliding.

"This is the most energetic cosmic event, besides the Big Bang, which we know about," said Maxim Markevitch of the Harvard-Smithsonian Center for Astrophysics and member of the NASA team that studied images collected with the Chandra X-ray observatory, the Hubble Space Telescope, the European Southern Observatory's Very Large Telescope and the Magellan optical telescopes.

The observation supports the theory that the bulk of the universe is made up of invisible dark matter, which was detected by observing the gravitational force it exerted on visible matter.

"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 team leader Doug Clowe of the University of Arizona at Tucson. "These results are direct proof that dark matter exists."

Because the force of gravity can bend light, the team was able to detect the presence of dark matter through gravitational lensing. Light emitted by objects that lie on the far side of the galaxy was distorted by a gravitational force in excess of the distortion expected by the visible matter present in the galactic collision. To make their discovery, the scientists trained their telescopes on a cluster of galaxies officially designated 1E0657-56, informally known as the bullet cluster because of its shape.

The bullet shape is the result of the violent collision of a small galaxy cluster with another, larger cluster as normal matter in the galaxies interacts during the collision. Dark matter, however, does not experience any of the forces that affect normal matter, other than gravity, and ended up separating from the normal matter during the event.

These results will be published in an upcoming issue of Astrophysical Journal Letters.

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