TheComa Cluster (Abell 1656) is a largecluster of galaxies that contains over 1,000 identified galaxies.[2][3] Along with theLeo Cluster (Abell 1367), it is one of the two major clusters comprising theComa Supercluster.[8] It is located in and takes its name from the constellationComa Berenices.
The cluster's mean distance fromEarth is 99Mpc (321 millionlight years).[3][9][10] Its ten brightest spiral galaxies haveapparent magnitudes of 12–14 that are observable with amateur telescopes larger than 20 cm.[11] The central region is dominated by two supergiantelliptical galaxies:NGC 4874 andNGC 4889.[12] 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.[13]
Tails inspiral galaxyD100, found in the Coma Cluster, are created by ram-pressure stripping.[14][15]
As is usual for clusters of this richness, the galaxies are overwhelmingly elliptical andS0 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 atMount Palomar Observatory, although many of the individual galaxies in the cluster had been identified previously.[16][17][18]
The Coma Cluster is one of the first places where observed gravitational anomalies were considered to be indicative of unobserved mass. In 1933Fritz Zwicky 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).[19][20]
About 90% of the mass of the Coma cluster is believed to be in the form ofdark matter. The distribution of dark matter throughout the cluster, however, is poorly constrained[clarification needed].[21]
An extended X-ray source centered at 1300+28 in the direction of the Coma cluster of galaxies was reported before August 1966.[22] This X-ray observation was performed by balloon, but the source was not detected in thesounding rocket flight launched by the X-ray astronomy group at theNaval Research Laboratory on November 25, 1964.[23] A strong X-ray source was observed by the X-ray observatory satelliteUhuru close to the center of the Coma cluster and this source was suggested to be designated Coma X-1.[24]
The Coma cluster contains about 800 galaxies within a 100 x 100 arc-min area of the celestial sphere. The source near the center atRA (1950) 12h56m ± 2mDec 28°6' ± 12' has a luminosity Lx = 2.6 x 1044 ergs/s.[24] 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.[24] The Uhuru observations indicated a source strength of no greater than ~10−3 photons cm−2s−1keV−1 at 25 keV,[24] which disagrees with the earlier observations[22] claiming a source strength of ~10−2 photons cm−2s−1keV−1 at 25 keV, and a size of 5°.
^Colless, M (2001)."Coma Cluster". In P Murdin (ed.).Encyclopedia of Astronomy and Astrophysics. Bristol Institute of Physics publishing. Retrieved2006-10-08.[permanent dead link]
^Shapley, Harlow (July 1934). "A Photometric Investigation of Wolf's Cluster of Nebulae in Coma".Harvard College Observatory Bulletin.896. Cambridge, MA, USA:3–12.Bibcode:1934BHarO.896....3S.
^Wallenquist, Å. (1933). "On the space distribution of the nebulae in the Coma Cluster".Annalen V.d. Bosscha-Sterrenwacht (Miscellaneous Papers (Observatorium Bosscha)).4 (6). France: Bandoeng : Gebrs. Kleijne:73–77.Bibcode:1933AnBos...4...73W.
^Zwicky, F. (1933)."Die Rotverschiebung von extragalaktischen Nebeln" [The red shift of extragalactic neubulae].Helvetica Physica Acta (in German).6:110–127.Bibcode:1933AcHPh...6..110Z. From p 125:"Um, wie beobachtet, einen mittleren Dopplereffekt von 1000 km/sek oder mehr zu erhalten, müsste also die mittlere Dichte im Comasystem mindestens 400 mal grösser sein als die auf Grund von Beobachtungen an leuchtender Materie abgeleitete. Falls sich dies bewahrheiten sollte, würde sich also das überraschende Resultat ergeben, dass dunkle Materie in sehr viel grösserer Dichte vorhanden ist als leuchtende Materie." (In order to obtain an average Doppler effect of 1000 km/s or more, as observed, the average density in the Coma system would thus have to be at least 400 times greater than that derived on the basis of observations of luminous matter. If this were to be verified, the surprising result would then follow that dark matter is present in very much greater density than luminous matter.)
![Thousands of globular clusters lying at the core of a galaxy cluster.[25]](/mt/?noimg=&dark=on&url=https%3a%2f%2fwikipedia.org%2fwiki%2fFile%3aClusters_within_clusters_-_Coma_Cluster.jpg)
![Hubble close-up on the Coma Cluster.[26]](/mt/?noimg=&dark=on&url=https%3a%2f%2fwikipedia.org%2fwiki%2fFile%3aHubble_close-up_on_the_Coma_Cluster.jpg)
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![Coma Cluster photographed through 8" Celestron Edge HD in San Diego, CA.[27]](/mt/?noimg=&dark=on&url=https%3a%2f%2fwikipedia.org%2fwiki%2fFile%3aComaGalaxy.jpg)
