XMM-Newton observation of Coma Cluster
Credit: left image: ESA; right image: Gregory Bothun, University of Oregon

Cosmic Cluster Mosaic: Dark Matter Revealed

Galaxies tend to congregate in groups called clusters, and such clusters are generally large, bright sources of X-rays. Some of the X-ray emission is produced by the individual galaxies, but most of the X-ray emission is produced by an enormous quantity of hot gas at the center of the cluster. The image above shows an X-ray image of the Coma Cluster of galaxies, obtained by the EPIC-pn X-ray cameras on XMM-Newton. The Coma cluster contains about 3000 galaxies, is about 280 million lightyears from earth, and stretches over 20 million lightyears. The image on the above left is a mosaic of 12 individual XMM-Newton images in the energy range 0.3-2.0 keV. The X-ray emission is dominated by the hot inter-galactic medium; since the free expansion of this hot gas is counteracted by gravity, measurement of the amount of hot gas by X-ray observations provides a measure of the total cluster mass, and usually shows that the total mass in the cluster is much larger than the mass estimated from the amount of luminous matter visible in optical images (like the one on the above right).

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Page Author: Dr. Michael F. Corcoran
Last modified April 4, 2002