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
