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Virgo clusterA giant irregular cluster of galaxies lying near the north galactic pole in the constellation Virgo. It is the nearest large cluster: its distance is currently estimated as 15 megaparsecs. Some 2500 galaxies have been observed of which about 75% are spirals, the remainder being mainly ellipticals with a few irregulars. Its second-brightest member, the giant elliptical galaxy M87, is both a radio source (Virgo A) and an X-ray source (Virgo X-1). The X-ray halo around M87 is taking part in a weak cooling flow of around 10 solar masses a year. A second large elliptical galaxy in Virgo, M86, is also an X-ray source, with the X-ray emission forming a plume directed away from the center of the galaxy. This is due to the hot gas being stripped from the galaxy by ram pressure as it falls into the cluster. The Virgo cluster is the center of the Local Supercluster, which exerts a significant gravitational pull on the Local Group of galaxies, reducing the measured recession velocity of the Virgo cluster by some 250 km s–1 (to about 1000 km s–1).
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
Virgo cluster[′vər·gō ‚kləs·tər]
A cluster of galaxies which is the nearest to the galaxy that includes the sun; the cluster is centered in the constellation Virgo and is about 1.6 × 107 light-years (1.51 × 1023 m) from earth.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.