Astronomy Montage

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Saturday, September 02, 2006

Dark Matter in Bullet Cluster


The "bullet cluster" is a galaxy cluster denoted 1E 0657-56 which was formed after the collision of two large clusters of galaxies(ie individual groups of galaxies)

This monumental energetic collision can only get surpassed by The Big Bang in terms of energy output, and has resulted in tearing apart dark matter from normal matter as an outcome of the collision.

The spectacular bullet cluster is composed of a hundred million degree bullet shaped cloud of gas, which is due to wind produced by the high speed collision of the two galactic clusters.

Because dark mater does not interact with the hot gas it was not slowed by the collisional drag force, wheras normal matter was slowed due to the collisonal drag force due to its interaction with the hot gas.

Xray imaging by the Chandra XRay Telescope showed this separation and thus provided the first direct evidence for dark matter.

It is formally known as 1E0657-56 and has coordinates: RA 06h 58m 37.9s | Dec -55ยบ 57' 0". It is about 4 billion light years from Earth in the constellation of Carina. The subcluster passed through the cluster center 150 million years ago creating a "bow-shaped shock wave located near the right side of the cluster" formed as "70 million degree Celsius gas in the sub-cluster plowed through 100 million degree gas in the main cluster at a speed of about 6 million miles per hour". Strictly speaking, the name Bullet cluster refers to the smaller subcluster, moving away from the larger one.

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