The Virgo Cluster of Galaxies

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The Virgo Cluster of Galaxies

Also: Coma-Virgo cluster of Galaxies

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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.

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:

M49,

M58,

M59,

M60,

M61,

M84,

M85,

M86,

M87,

M88,

M89,

M90,

M91,

M98,

M99,

and M100.


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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 chanin 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.

HST observations of Cepheids in M100,

as well as estimates from the globular cluster luminosity in

M87,

together with the work of

Nial R. Tanvir and, again,

HST observations, on the M96 group,

extrapolated to this cluster, indicate that the Virgo cluster is at

a distance of some 60 million light-years.


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