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 galaxy, galaxies that are bound together by gravity, with typical masses ranging from 1014 to 1015 solar masses. Clusters consist o ...

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 that includes the Coma Cluster (Abell 1656) and the Leo Cluster (Abell 1367). Located 300 million light-years from Earth in the constellation Coma Berenices, it is in the cen ...

. 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 hemispher ...

. The cluster's mean distance from

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

is 99 Mpc (321 million

light year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distance, astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by t ...

s). Its ten brightest spiral galaxies have

apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

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 three main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work ''The Re ...

NGC 4874 NGC 4874 is a supergiant elliptical galaxy. It was discovered by the British astronomer Frederick William Herschel I in 1785, who catalogued it as a bright patch of nebulous feature. The second-brightest galaxy within the northern Coma Cluster, ...

and NGC 4889. 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 The Palomar Observatory is an astronomical research observatory in the Palomar Mountain, Palomar Mountains of San Diego County, California, United States. It is owned and operated by the California Institute of Technology (Caltech). Research time ...

, 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 an ...

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 In astronomy, dark matter is an invisible and hypothetical form of matter that does not interact with light or other electromagnetic radiation. Dark matter is implied by gravity, gravitational effects that cannot be explained by general relat ...

. 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 often ...

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. Located in Washington, DC, it was founded in 1923 and conducts basic scientific research, appl ...

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:Coma cluster.png, Coma cluster by amateur astrophotographer Anthony MICHEL File:Comacl zentrum600.png, Map of the central part of the Coma Cluster.

References

External links

The Coma Cluster of Galaxies
–

Astronomy Picture of the Day Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest include ...

, NASA, 2000 August 6
The clickable Coma galaxy cluster

The dynamical state of the Coma cluster with XMM-Newton

Very Small Array observations of the Sunyaev-Zel'dovich effect in nearby galaxy clusters

* {{DEFAULTSORT:Coma Cluster Galaxy clusters Coma Supercluster Coma Berenices

1656 Events January–March * January 5 – The First War of Villmergen, a civil war in the Old Swiss Confederacy, Confederation of Switzerland pitting its Protestant and Roman Catholic Swiss canton, cantons against each other, breaks o ...