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The Virgo Cluster (VC) is a cluster of galaxies whose center is 53.8 ± 0.3 Mly (16.5 ± 0.1 Mpc) away in the constellation Virgo. Comprising approximately 1300 (and possibly up to 2000) member galaxies,〔See (Virgo Cluster ).〕 the cluster forms the heart of the larger Virgo Supercluster, of which the Local Group (LG) is an outlying member. However, the LG experiences the mass of the VC Supercluster as the Virgocentric flow. It is estimated that the VC's mass is 1.2 out to 8 degrees of the cluster's center or a radius of about 2.2 Mpc. Many of the brighter galaxies in this cluster, including the giant elliptical galaxy Messier 87, were discovered in the late 1770s and early 1780s and subsequently included in Charles Messier's catalogue of non-cometary fuzzy objects. Described by Messier as nebulae without stars, their true nature was not recognized until the 1920s.〔Following the entry for M91 in the Connoissance des Temps for 1784, Messier added the following note: : ''The constellation of Virgo, & especially the northern Wing is one of the constellations which encloses the most Nebulae: this Catalog contains thirteen which have been determined: viz. Nos. 49, 58, 59, 60, 61, 84, 85, 86, 87, 88, 89, 90, & 91. All these nebulae appear to be without stars: one can see them only in a very good sky, & near their meridian passage. Most of these nebulae have been pointed to me by Mr. Méchain.'' (see (M91 ).)〕 The cluster subtends a maximum arc of approximately 8 degrees centered in the constellation Virgo. Many of the member galaxies of the cluster are visible with a small telescope. Its brightest member is the elliptical galaxy Messier 49; however its most famous member is the also elliptical galaxy Messier 87, that unlike the former is located in the center of the cluster. == Characteristics == The cluster is a fairly heterogeneous mixture of spirals and ellipticals.〔 〕 , it is believed that the spirals of the cluster are distributed in an oblong prolate filament, approximately four times as long as it is wide, stretching along the line of sight from the Milky Way. The elliptical galaxies are more centrally concentrated than the spiral galaxies. The cluster is an aggregrate of at least three separate subclumps: ''Virgo A'', centered on M87, a second centered on the galaxy M86, and ''Virgo B'', that surrounds M49, with some authors including a ''Virgo C'' subcluster, centered on the galaxy M60 as well as a ''LVC'' (Low Velocity Cloud) subclump, centered on the large spiral galaxy NGC 4216.〔 〕 Of all of them, ''Virgo A'', formed by a mixture of elliptical, lenticular, and -usually- gas-poor spiral galaxies,〔 〕 is the dominant one, with a mass of approximately 1014 , which is approximately an order of magnitude larger than the other two subclumps.〔''(The Virgo Super Cluster: home of M87 )'' (with frames)〕 The three subgroups are in the process of merging to form a larger single cluster〔 and are surrounded by other smaller galaxy clouds, mostly composed of spiral galaxies, known as ''N Cloud'', ''S Cloud'', and ''Virgo E'' that are in the process of infalling to merge with them, plus other farther isolated galaxies and galaxy groups (like the galaxy cloud Coma I) that are also attracted by the gravity of Virgo to merge with it in the future. This strongly suggests the Virgo cluster is a dynamically young cluster that is still forming.〔 Other two nearby aggregations known as ''M Cloud'', ''W Cloud'', and ''W' Cloud''〔 seem to be background systems independent of the main cluster.〔 The large mass of the cluster is indicated by the high peculiar velocities of many of its galaxies, sometimes as high as 1,600 km/s with respect to the cluster's center. The Virgo cluster lies within the Virgo Supercluster, and its gravitational effect slows down the nearby galaxies. The large mass of the cluster has the effect of slowing down the recession of the Local Group from the cluster by approximately ten percent. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Virgo Cluster」の詳細全文を読む スポンサード リンク
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