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Groups and Clusters

Galaxy groups and clusters are the largest gravitationally-bound objects in the Universe. Groups and clusters may contain from ten to thousands of galaxies. The clusters themselves are often associated with larger groups called superclusters. Groups of galaxies are the smallest aggregates of galaxies. They typically contain fewer than 50 galaxies in a diameter of 1 to 2 megaparsecs (3 to 6 million light-years). Their mass is approximately ten trillion solar masses. The group which contains our own galaxy, the Milky Way, is called the Local Group, and contains more than 40 galaxies. Clusters are larger than groups, although there is no sharp dividing line between the two.

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Galaxy Clusters Last Updated on 2007-11-08 00:00:00 THIS IS A PROTO-ARTICLE, UNDER CONSTRUCTION. FURTHER DEVELOPMENT IS ENCOURAGED. On equivalent spatial scales, galaxy clusters are the largest perturbations to the cosmic matter density. Gravitational potential wells set by dark matter are populated with galaxies and intracluster baryons, including stars and gas. R~1-2 Mpc (Megaparsec) in radius. M~1013-1015M_{sol} in mass. There exist anywhere from two to 1000's of galaxies in a cluster. The Milky Way resides in the Local Group which includes the Large and Small Magellanic Clouds. Observable in a large range of wavelengths, including the optical, X-ray, and radio; these correspond with a suite of labeling parameters, which relate to the underlyling mass distribution; the characterization of the mass function. Contain evolution of large-scale structure as tracers of the cosmic matter distribution. Laboratories for testing of... More »