The Coma Cluster (Abell 1656) is a large

cluster of galaxies A galaxy cluster, or a cluster of galaxies, is a structure that consists of anywhere from hundreds to thousands of galaxies that are bound together by gravity, with typical masses ranging from 1014 to 1015 solar masses. They are the second-lar ...

that contains over 1,000 identified galaxies. Along with the Leo Cluster (Abell 1367), it is one of the two major clusters comprising the

Coma Supercluster The Coma Supercluster (SCl 117) is a nearby supercluster of galaxies comprising the Coma Cluster (Abell 1656) and the Leo Cluster (Abell 1367). Located 300 million light-years from Earth, it is in the center of the Great Wall and a part of the Co ...

. It is located in and takes its name from the constellation

Coma Berenices Coma Berenices is an ancient asterism in the northern sky, which has been defined as one of the 88 modern constellations. It is in the direction of the fourth galactic quadrant, between Leo and Boötes, and it is visible in both hemisphe ...

. The cluster's mean distance from Earth is 99 Mpc (321 million

light year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s). Its ten brightest spiral galaxies have

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

s of 12–14 that are observable with amateur telescopes larger than 20 cm. The central region is dominated by two supergiant

elliptical galaxies An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the four main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work ''The Real ...

: NGC 4874 and

NGC 4889 NGC 4889 (also known as Caldwell 35) is an E4 supergiant elliptical galaxy. It was discovered in 1785 by the British astronomer William Herschel, Frederick William Herschel I, who catalogued it as a bright, nebulous patch. The brightest galaxy wi ...

. The cluster is within a few degrees of the north galactic pole on the sky. Most of the galaxies that inhabit the central portion of the Coma Cluster are ellipticals. Both dwarf and giant ellipticals are found in abundance in the Coma Cluster.

Cluster members

As is usual for clusters of this richness, the galaxies are overwhelmingly elliptical and S0 galaxies, with only a few spirals of younger age, and many of them probably near the outskirts of the cluster. The full extent of the cluster was not understood until it was more thoroughly studied in the 1950s by astronomers at

Mount Palomar Observatory Palomar Observatory is an astronomical research observatory in San Diego County, California, United States, in the Palomar Mountain Range. It is owned and operated by the California Institute of Technology (Caltech). Research time at the observat ...

, although many of the individual galaxies in the cluster had been identified previously.

Dark matter

The Coma Cluster is one of the first places where observed gravitational anomalies were considered to be indicative of unobserved mass. In 1933

Fritz Zwicky Fritz Zwicky (; ; February 14, 1898 – February 8, 1974) was a Swiss astronomer. He worked most of his life at the California Institute of Technology in the United States of America, where he made many important contributions in theoretical and ...

showed that the galaxies of the Coma Cluster were moving too fast for the cluster to be bound together by the visible matter of its galaxies. Though the idea of dark matter would not be accepted for another fifty years, Zwicky wrote that the galaxies must be held together by "''dunkle Materie''" (dark matter). About 90% of the mass of the Coma cluster is believed to be in the form of

dark matter Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not ab ...

. The distribution of dark matter throughout the cluster, however, is poorly constrained.

X-ray source

An extended X-ray source centered at 1300+28 in the direction of the Coma cluster of galaxies was reported before August 1966. This X-ray observation was performed by balloon, but the source was not detected in the

sounding rocket A sounding rocket or rocketsonde, sometimes called a research rocket or a suborbital rocket, is an instrument-carrying rocket designed to take measurements and perform scientific experiments during its sub-orbital flight. The rockets are used to ...

flight launched by the X-ray astronomy group at the

Naval Research Laboratory The United States Naval Research Laboratory (NRL) is the corporate research laboratory for the United States Navy and the United States Marine Corps. It was founded in 1923 and conducts basic scientific research, applied research, technological ...

on November 25, 1964. A strong X-ray source was observed by the X-ray observatory satellite Uhuru close to the center of the Coma cluster and this source was suggested to be designated Coma X-1. The Coma cluster contains about 800 galaxies within a 100 x 100 arc-min area of the celestial sphere. The source near the center at RA (1950) 12^h56^m ± 2^m Dec 28°6' ± 12' has a luminosity L_x = 2.6 x 10⁴⁴ ergs/s. As the source is extended, with a size of about 45', this argues against the possibility that a single galaxy is responsible for the emission. The Uhuru observations indicated a source strength of no greater than ~10⁻³ photons cm⁻²s⁻¹keV⁻¹ at 25 keV, which disagrees with the earlier observations claiming a source strength of ~10⁻² photons cm⁻²s⁻¹keV⁻¹ at 25 keV, and a size of 5°.

Gallery

File:Clusters within clusters - Coma Cluster.jpg, Thousands of globular clusters lying at the core of a galaxy cluster. File:The Coma Galaxy Cluster as seen by Hubble Heic0813a.jpg, A large portion of the Coma Cluster seen by Hubble's Advanced Camera for Surveys File:Hubble close-up on the Coma Cluster.jpg, Hubble close-up on the Coma Cluster. File:NGC 4911.jpg, A face-on view of a spiral galaxy ( NGC 4911) located deep within the Coma Cluster. File:Coma Cluster of Galaxies (visible, wide field).jpg, Wide field image of the Coma Cluster taken at the Mount Lemmon SkyCenter using the 0.8m Schulman Telescope. File:ComaGalaxy.jpg, Coma Cluster photographed through 8" Celestron Edge HD in San Diego, CA. File:Comacl zentrum600.png, Map of the central part of the Coma Cluster.

References

External links

The Coma Cluster of Galaxies
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