This giant agglomeration of galaxies is the nearest big cluster of galaxies, the largest proven structure in our intergalactic neighborhood, and the most remote cosmic objects with a physical connection to our own small group of galaxies, the Local Group, including our Milky Way galaxy. This structure is another discovery by Charles Messier, who noted behind his entry for M91 (here quoted from Kenneth Glyn Jones' book):
``The constellation Virgo and especially the northern wing is one of the constellations which encloses the most nebulae. This catalogue contains 13 which have been determined, viz. Nos. 49, 58, 59, 60, 61, 84, 85, 86, 87, 88, 89, 90 and 91. All these nebulae appear to be without stars and can be seen only in a good sky and near meridian passage. Most of these nebulae have been pointed out to me by M. Mechain.''Together with his later entries, 98, 99, and 100, Messier had cataloged 16 members of the Virgo cluster which he viewed as a `cluster of nebulae'. Our image shows a star chart drawn by Messier, cropped from a larger chart he published with his observations of the comet of 1779 (all 16 Messier objects are marked in this drawing). This discovery occured in 1781, significantly more than a century before the true nature of galaxies was realized in the 1920s ! A long history of exploration still had to pass until its nature as a physical cluster of galaxies became obvious.
Messier galaxies which are Virgo cluster members:
The Virgo Cluster with its some 2000 member galaxies dominates our intergalactic neighborhood, as it represents the physical center of our Local Supercluster (also called Virgo or Coma-Virgo Supercluster), and influences all the galaxies and galaxy groups by the gravitational attraction of its enormous mass. It has slowed down the escape velocities (due to cosmic expansion, the `Hubble effect') of all the galaxies and galaxy groups around it, thus causing an effective matter flow towards itself (the so-called Virgo-centric flow). Eventually many of these galaxies have fallen, or will fall in the future, into this giant cluster which will increase in size due to this effect. Our Local Group has experienced a speed-up of 100..400 km/sec towards the Virgo cluster. Current data on the mass and velocity of the Virgo cluster indicate that the Local Group is probably not off far enough to escape, so that its recession from Virgo will probably be halted at one time, and then it will fall and merge into, or be eaten by the cluster, see our Virgo Cluster & Local Group page.
Because of the Virgo Cluster's enormous mass, its strong gravity accelerates the member galaxies to considerably high peculiar velocities, up to over 1500 km/sec, with respect to the cluster's center of mass. Investigations over the past decades have revealed a quite complex dynamic structure of this huge irregular aggregate of galaxies. The Virgo cluster is close enough that some of its galaxies, which happen to move fast through the cluster in our direction, exhibit the highest blue-shifts (instead of cosmological redshifts) measured for any galaxies, i.e. are moving toward us: The record stands for IC 3258, which is approaching us at 517 km/sec. As the cluster is receding from us at about 1,100 km/sec, this galaxy must move with over 1,600 km/sec through the Virgo Cluster's central region. Analogously, those galaxies which happen to move fastest away from us through the cluster, are receding at more than double redshift than the cluster's center of mass: The record is hold by NGC 4388 at 2535 km/sec, so that this galaxy moves peculiarly in the direction away from us at over 1,400 km/sec.
Our image shows the central portion of the Virgo Cluster of Galaxies, and is centered on the giant elliptical galaxy M87 which is considered to be the dominant galaxy of the whole giant cluster, situated close to its physical center. The two bright galaxies on the right (west) are (right-to-left) M84 and M86; starting from these two, a chain of galaxies ("Markarian's chain") stretches well to the upper (northern) middle of our image (and beyond, well to M88 which is slightly outside above the sky area photographed our image). The appealing group around these two giant lenticulars is described with M84, and in our collection of images with M84 and M86; we also have images of M87 together with Markarian's chain around M84 and M86. To the left (east) of M87, the considerably bright elliptical (type E0) M89 occurs (on roughly the same declination as M87), above it and slightly more left is the inclined and conspicuous spiral M90, while below (south) and left of M89 there is M58, sitting just on the edge of our image.
References for further reading:
Last Modification: 7 Feb 2000, 14:14 MET