Coma cluster of galaxies
Encyclopedia
The Coma Cluster is a large cluster of galaxies
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
. It is located in and takes its name from the constellation Coma Berenices
.
The cluster's mean distance from Earth is 99 Mpc
(321 million light years). Its ten brightest spiral galaxies have apparent magnitude
s of 12–14 that are observable with amateur telescopes larger than 20 cm. The central region is dominated by two giant elliptical galaxies
: NGC 4874
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, as well as giant ellipticals, are found in abundance in the Coma 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.
.
However, the distribution of dark matter throughout the cluster is poorly constrained.
flight launched by the X-ray astronomy group at the Naval Research Laboratory 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 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) 12h56m ± 2m Dec
28°6' ± 12' has a luminosity Lx = 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°.
Galaxy cluster
A galaxy cluster is a compact cluster of galaxies. Basic difference between a galaxy group and a galaxy cluster is that there are many more galaxies in a cluster than in a group. Also, galaxies in a cluster are more compact and have higher velocity dispersion. One of the key features of cluster is...
that contains over 1,000 identified galaxies. Along with the Leo Cluster
Leo Cluster
The Leo Cluster is a galaxy cluster about 330 million light-years distant in the constellation Leo. Along with the Coma Cluster, it is one of the two major clusters comprising the Coma Supercluster-External links:...
(Abell 1367), it is one of the two major clusters comprising the Coma Supercluster
Coma Supercluster
The Coma Supercluster is a nearby supercluster of galaxies comprising the Coma Cluster and the Leo Cluster . Located 300 million light-years from Earth, it is in the center of the Great Wall. The Coma Supercluster is the nearest massive cluster of galaxies to our own Virgo Supercluster...
. It is located in and takes its name from the constellation Coma Berenices
Coma Berenices
Coma Berenices is a traditional asterism that has since been defined as one of the 88 modern constellations. It is located near Leo, to which it formerly belonged, and accommodates the North Galactic Pole...
.
The cluster's mean distance from Earth is 99 Mpc
Parsec
The parsec is a unit of length used in astronomy. It is about 3.26 light-years, or just under 31 trillion kilometres ....
(321 million light years). Its ten brightest spiral galaxies have apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
s of 12–14 that are observable with amateur telescopes larger than 20 cm. The central region is dominated by two giant elliptical galaxies
Elliptical galaxy
An elliptical galaxy is a galaxy having an approximately ellipsoidal shape and a smooth, nearly featureless brightness profile. They range in shape from nearly spherical to highly flat and in size from hundreds of millions to over one trillion stars...
: NGC 4874
NGC 4874
NGC 4874 is giant elliptical galaxy, about ten times larger than the Milky Way, at the centre of the Coma Galaxy Cluster. With its strong gravitational pull, it is able to hold onto more than 30.000 globular clusters of stars and even has a few dwarf galaxies in its grasp....
and NGC 4889
NGC 4889
NGC 4889, also known as Caldwell 35, is a supergiant class-4 elliptical galaxy, the brightest within the Coma cluster and a Caldwell object in the constellation Coma Berenices. It shines at magnitude +11.4. Its celestial coordinates are RA 13h00.1m, DEC +27°59'...
. 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, as well as 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, although many of the individual galaxies in the cluster had been identified previously.
Dark matter
About 90% of the mass of the Coma cluster is believed to be in the form of dark matterDark matter
In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...
.
However, the distribution of dark matter throughout the cluster 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 rocketSounding rocket
A sounding rocket, sometimes called a research rocket, is an instrument-carrying rocket designed to take measurements and perform scientific experiments during its sub-orbital flight. The origin of the term comes from nautical vocabulary, where to sound is to throw a weighted line from a ship into...
flight launched by the X-ray astronomy group at the Naval Research Laboratory on November 25, 1964. A strong X-ray source was observed by the X-ray observatory satellite Uhuru
Uhuru (satellite)
Uhuru was the first satellite launched specifically for the purpose of X-ray astronomy. It was also known as the X-ray Explorer Satellite, SAS-A , SAS 1, or Explorer 42.The observatory was launched on 12 December 1970 into an initial orbit of about 560 km apogee, 520 km...
close to the center of the Coma cluster and this source was suggested 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
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
(1950) 12h56m ± 2m Dec
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
28°6' ± 12' has a luminosity Lx = 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°.
See also
- Fornax ClusterFornax ClusterAt a distance of approximately 62.0 Mly , the Fornax Cluster is the second richest cluster of galaxies within 100 million light-years, although it is much smaller than the Virgo Cluster. It lies primarily in the constellation Fornax, and may be associated with the nearby Eridanus Group...
- another nearby cluster of galaxies - Virgo ClusterVirgo ClusterThe Virgo Cluster is a cluster of galaxies whose center is 53.8 ± 0.3 Mly away in the constellation Virgo. Comprising approximately 1300 member galaxies, the cluster forms the heart of the larger Local Supercluster, of which the Local Group is an outlying member...
- another nearby cluster of galaxies - X-1 X-ray source
External links
- The Coma Cluster of Galaxies - Astronomy Picture of the DayAstronomy Picture of the DayAstronomy Picture of the Day is a website provided by NASA and Michigan Technological University . According to the website, "Each day a different image or photograph of our universe is featured, along with a brief explanation written by a professional astronomer."The photograph is not necessarily...
, NASA, 2000 August 6 - The dynamical state of the Coma cluster with XMM-Newton
- Very Small Array observations of the Sunyaev-Zel'dovich effect in nearby galaxy clusters
- Hubble Space Telescope Treasury Survey of the Coma Cluster