|
A sky field near some of the brighter galaxies in the Virgo cluster. The most prominent galaxies are marked but inspection of the
Larger Version of this picture will show dozens more. The large elliptical galaxy at the centre is Messier 84; the elongated
image of NGC 4388 (an active spiral galaxy) is in the lower left corner.
The Virgo cluster is a cluster of galaxies,
approximately 15 to 22 Mpc distant, comprising approximately 1300 (and possibly
up to 2000) member galaxies. The cluster forms the heart of the larger Local supercluster, of which the Local Group is an
outlying member.
The cluster was discovered by Charles Messier in 1781, who charted many of its prominent member galaxies, including the giant M87 galaxy.
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. The distance to the cluster is
still an open question, with current best guesses, based on Cepheids using the
Hubble Space Telescope, yielding an average of
approximately 20 Mpc [1] .
The cluster is a fairly heterogenous mixture of spirals and ellipticals. It is currently believed that the spirals of the cluster are distributed in a cigar-shaped prolate filament, approximately 4 times as long as wide, stretching along
the line of sight from the Milky Way and connecting on its back end to the W cloud
[2] . The
ellipticals are concentrated much more than the spirals.
The cluster is an aggregrate of at least three separate subclumps centered on
the galaxies M87, M86, and M49. Of the three subclumps, the
one centered on M87 is the dominant one, with a mass of approximately 1014 solar masses, which is approximately an
order of magnitude larger than other the other two subclumps [3] .
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.
Within the Local supercluster, and its gravitational effects
slow 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.
More info:
|