The Virgo Cluster 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, the cluster forms the heart of the larger Virgo Supercluster, of which the Local Group (containing the Milky Way galaxy) is an outlying member. The Local Group actually experiences the mass of the Virgo Supercluster as the Virgocentric flow. It is estimated that the Virgo Cluster's mass is 1.2×1015 M☉ 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.[A]
The cluster subtends a maximum arc of approximately 8 degrees centered in the constellation Virgo. Although some of the cluster's most prominent members can be seen with smaller instruments, a 6 inch telescope will reveal about 160 of the cluster's galaxies on a clear night. Its brightest member is the elliptical galaxy Messier 49; however its most famous member is the elliptical galaxy Messier 87, which is located in the center of the cluster.
|Observation data (Epoch J2000)|
|Constellation(s)||Virgo & Coma Berenices|
|Right ascension||12h 27m|
|Brightest member||Messier 49|
|Number of galaxies||~1500|
The cluster is a fairly heterogeneous mixture of spirals and ellipticals. As of 2004, it is believed that the spiral galaxies 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, centered on 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 the subclumps, 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 M☉, which is approximately an order of magnitude larger than the other two subclumps.
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.
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.
The Virgo cluster's thermal conduction follows magnetic field lines, so magnetic fields strongly shape the cluster’s thermal history; that some have not since cooled and collapsed is a mystery. Recent observations of Virgo cluster spiral galaxies imply ridges of strong, coherent magnetic fields offset from their center. This observation can be explained by galaxies sweeping up field lines as they orbit inside the cluster. This magnetic drape is then lit up with cosmic rays from the galaxies’ stars, generating coherent polarized emission at the galaxies’ leading edges. This immediately presents a technique for probing local orientations and characteristic length scales of cluster magnetic fields. The first application of this technique, mapping the field of the Virgo cluster, gives a startling result: outside a central region, the magnetic field is preferentially oriented radially as predicted by the magnetothermal instability. The results strongly suggest a mechanism for maintaining some clusters in a ‘non-cooling-core’ state.
As with many other rich galaxy clusters, Virgo's intracluster medium is filled with a hot, rarefied plasma at temperatures of 30 million kelvins that emits X-Rays. Within the intracluster medium (ICM) are found a large number of intergalactic stars (up to 10% of the stars in the cluster), including some planetary nebulae. It is theorized that these were expelled from their home galaxies by interactions with other galaxies. The ICM also contains some globular clusters, possibly stripped off dwarf galaxies, and even at least one star formation region.
Below is given a table of bright or notable objects in the Virgo Cluster and the subunit of the cluster in which they are located. Note that in some cases a galaxy may be considered in a different subunit by other researchers (sources:)
|Designation||Coordinates (Epoch 2000)||Apparent
|Messier 98||12 13.8||14 54||10.9||SBb||9.8′||150||184||Virgo A or N Cloud|
|NGC 4216||12 15.9||13 09||10.9||SBb||7.9′||120||459||Virgo A, N Cloud, or LVC.|
|Messier 99||12 18.8||14 25||10.4||Sc||5.4′||80||2735||Virgo A or N Cloud|
|NGC 4262||12 19.5||14 53||12.4||S0||1.9′||30||1683||Virgo A|
|NGC 4388||12 25.5||12 39||11.8||SAb||6.2′||85||2845||Virgo A|
|Messier 61||12 21.9||04 28||10.2||SBbc||6.2′||100||1911||S Cloud|
|Messier 100||12 22.9||15 49||10.1||SBbc||7.6′||115||1899||Virgo A|
|Messier 84||12 25.1||12 53||10.1||E1||6.0′||90||1239||Virgo A|
|Messier 85||12 25.4||18 11||10.0||S0||7.1′||105||1056||Virgo A|
|Messier 86||12 26.2||12 57||9.9||E3||10.2′||155||37||Virgo A or own subgroup.|
|NGC 4435||12 27.7||13 05||11.7||S0||3.0′||45||1111||Virgo A|
|NGC 4438||12 27.8||13 01||11.0||Sa||8.7′||130||404||Virgo A|
|NGC 4450||12 28.5||17 05||10.9||Sab||5.1′||80||2273||Virgo A|
|Messier 49||12 29.8||08 00||9.3||E2||9.8′||150||1204||Virgo B|
|Messier 87||12 30.8||12 23||9.6||E0-1||9.8′||150||1204||Virgo A|
|Messier 88||12 32.0||14 25||10.3||Sb||6.8′||100||2599||Virgo A|
|NGC 4526||12 32.0||07 42||10.6||S0||7.1′||105||931||Virgo B|
|NGC 4527||12 34.1||02 39||12.4||Sb||4.6′||69||1730||S Cloud|
|NGC 4536||12 34.4||02 11||11.1||SBbc||7.2′||115||2140||S Cloud|
|Messier 91||12 35.4||14 30||11.0||SBb||5.2′||80||803||Virgo A|
|NGC 4550||12 35.5||12 13||12.5||S0||3.2′||50||704||Virgo A|
|Messier 89||12 35.7||12 33||10.7||E0||5.0′||75||628||Virgo A|
|NGC 4567||12 36.5||11 15||12.1||Sbc||2.8′||40||2588||Virgo A|
|NGC 4568||12 36.6||11 14||11.7||Sbc||4.4′||65||2578||Virgo A|
|Messier 90||12 36.8||13 10||10.2||SBab||10.5′||160||87||Virgo A|
|NGC 4571||12 36.9||14 13||11.9||Sc||3.7′||55||659||Virgo A|
|Messier 58||12 37.7||11 49||10.6||SBb||5.6′||85||1839||Virgo A|
|Messier 59||12 42.9||11 39||10.8||E5||5.0′||75||751||Virgo A or Virgo E|
|Messier 60||12 43.7||11 33||9.8||E2||7.2′||110||1452||Virgo A, Virgo E, or Virgo C|
|NGC 4651||12 43.7||16 24||11.4||Sc||4.0′||60||1113|
|NGC 4654||12 43.9||13 08||11.1||SBc||5.0′||75||1349||Virgo A|
Fainter galaxies within the cluster are usually known by their numbers in the Virgo Cluster Catalog, particularly members of the numerous dwarf galaxy population.
The nearest large groups of elliptical galaxies, in the Virgo and Fornax clusters, play a central role in determinations of the Hubble constant, H0, and hence the cosmological rate of expansion. Because the relative distances between these two clusters and more remote clusters are well known, absolute distance determinations to Virgo and Fornax should establish the Hubble constant for the local Universe. In addition, elliptical galaxies reside predominantly in the cores of clusters, so distance calibrations for ellipticals should minimize the uncertainties due to the possibly large extent of the clusters along the line of sight. A powerful and direct way of establishing such distances is to use the brightest red-giant stars, which have nearly uniform luminosities. The direct observation of old red-giant stars in a dwarf elliptical galaxy in the Virgo cluster was reported in a paper in Nature. It was determined that the distance to this galaxy, and thus to the core of the Virgo cluster, was 15.7 ± 1.5 megaparsecs, from which they estimated a Hubble constant of H0 = 77 ± 8 km s−1 Mpc−1. Under the assumption of a low-density Universe with the simplest cosmology, they estimated the age of the Universe to be no more than 12–13 billion years; not bad for a paper written twenty years ago.