Coma Cluster

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Coma Cluster
Coma cluster leo.jpg
Coma cluster of galaxies photographed by an amateur
Observation data (Epoch J2000)
Constellation(s) Coma Berenices
Right ascension 12h 59m 48.7s [1]
Declination +27° 58 50 [1]
Brightest member NGC 4874 and NGC 4889
Number of galaxies> 1000 [2] [3]
Richness class 2 [4]
Bautz–Morgan classification II [4]
Velocity dispersion 1,000 km/s [5]
Redshift 0.0231 (6 925 km/s) [1]
Distance 102.975  Mpc (336  Mly) for h1
0.705
[1]
ICM temperature 8-9 keV [6]
Binding mass ~7×1014 [7]   M
X-ray flux (319.20 ± 2.6%)×10−12 erg s−1 cm−2 [1] (0.1-2.4 keV) [1]
Other designations
Abell 1656 [1]
See also: Galaxy group, Galaxy cluster, List of galaxy groups and clusters

The Coma Cluster (Abell 1656) is a large cluster of galaxies that contains over 1,000 identified galaxies. [2] [3] Along with the Leo Cluster (Abell 1367), it is one of the two major clusters comprising the Coma Supercluster. [8] It is located in and takes its name from the constellation Coma Berenices.

Contents

The cluster's mean distance from Earth is 99 Mpc (321 million light years). [3] [9] [10] Its ten brightest spiral galaxies have apparent magnitudes of 12–14 that are observable with amateur telescopes larger than 20 cm. [11] The central region is dominated by two supergiant elliptical galaxies: NGC 4874 and NGC 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]

Cluster members

Tails in spiral galaxy D100, found in the Coma Cluster, are created by ram-pressure stripping. Wading through water.jpg
Tails in spiral galaxy D100, found in the Coma Cluster, are created by ram-pressure stripping.

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, although many of the individual galaxies in the cluster had been identified previously. [16] [17] [18]

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 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 of dark matter. The distribution of dark matter throughout the cluster, however, is poorly constrained[ clarification needed ]. [21]

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. [22] This X-ray observation was performed by balloon, but the source was not detected in the sounding rocket flight launched by the X-ray astronomy group at the Naval Research Laboratory on November 25, 1964. [23] 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. [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 at RA (1950) 12h56m ± 2m Dec 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°.

See also

Related Research Articles

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In astronomy, dark matter is a hypothetical form of matter that appears not to interact with light or the electromagnetic field. Dark matter is implied by gravitational effects which cannot be explained by general relativity unless more matter is present than can be seen. Such effects occur in the context of formation and evolution of galaxies, gravitational lensing, the observable universe's current structure, mass position in galactic collisions, the motion of galaxies within galaxy clusters, and cosmic microwave background anisotropies.

<span class="mw-page-title-main">Galaxy</span> Large gravitationally bound system of stars and interstellar matter

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<span class="mw-page-title-main">Messier 87</span> Elliptical galaxy in the Virgo Galaxy Cluster

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<span class="mw-page-title-main">Pinwheel Galaxy</span> Galaxy in the constellation Ursa Major

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<span class="mw-page-title-main">Fritz Zwicky</span> Swiss astronomer (1898–1974)

Fritz Zwicky 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 observational astronomy. In 1933, Zwicky was the first to use the virial theorem to postulate the existence of unseen dark matter, describing it as "dunkle Materie".

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<span class="mw-page-title-main">IC 1101</span> Galaxy in the constellation Virgo

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<span class="mw-page-title-main">Maffei 1</span> Galaxy in the constellation Cassiopeia

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<span class="mw-page-title-main">Abell 1413</span> Galaxy cluster in constellation Coma Berenices

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<span class="mw-page-title-main">NGC 4494</span> Galaxy in the constellation Coma Berenices

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<span class="mw-page-title-main">NGC 4636</span> Galaxy in the constellation Virgo

NGC 4636 is an elliptical galaxy located in the constellation Virgo. It is a member of the NGC 4753 Group of galaxies, which is a member of the Virgo II Groups, a series of galaxies and galaxy clusters strung out from the southern edge of the Virgo Supercluster. It is located at a distance of about 55 million light years from Earth, which, given its apparent dimensions, means that NGC 4636 is about 105,000 light years across.

<span class="mw-page-title-main">NGC 547</span> Galaxy in the constellation Cetus

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References

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