Galaxy cluster

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Composite image of five galaxies clustered together just 600 million years after the Universe's birth BoRG-58.jpg
Composite image of five galaxies clustered together just 600 million years after the Universe's birth

A galaxy cluster, or cluster of galaxies, is a structure that consists of anywhere from hundreds to thousands of galaxies that are bound together by gravity [1] with typical masses ranging from 1014–1015 solar masses. They are the largest known gravitationally bound structures in the universe and were believed to be the largest known structures in the universe until the 1980s, when superclusters were discovered. [2] One of the key features of clusters is the intracluster medium (ICM). The ICM consists of heated gas between the galaxies and has a peak temperature between 2–15 keV that is dependent on the total mass of the cluster. Galaxy clusters should not be confused with star clusters, such as galactic clusters—also known as open clusters—which are structures of stars within galaxies, or with globular clusters, which typically orbit galaxies. Small aggregates of galaxies are referred to as galaxy groups rather than clusters of galaxies. The galaxy groups and clusters can themselves cluster together to form superclusters.


Notable galaxy clusters in the relatively nearby Universe include the Virgo Cluster, Fornax Cluster, Hercules Cluster, and the Coma Cluster. A very large aggregation of galaxies known as the Great Attractor, dominated by the Norma Cluster, is massive enough to affect the local expansion of the Universe. Notable galaxy clusters in the distant, high-redshift Universe include SPT-CL J0546-5345 and SPT-CL J2106-5844, the most massive galaxy clusters found in the early Universe. In the last few decades, they are also found to be relevant sites of particle acceleration, a feature that has been discovered by observing non-thermal diffuse radio emissions, such as radio halos and radio relics. Using the Chandra X-ray Observatory, structures such as cold fronts and shock waves have also been found in many galaxy clusters.

Basic properties

Galaxy cluster IDCS J1426 is located 10 billion light-years from Earth and has the mass of almost 500 trillion suns. Galaxy cluster IDCS J1426.jpg
Galaxy cluster IDCS J1426 is located 10 billion light-years from Earth and has the mass of almost 500 trillion suns.

Galaxy clusters typically have the following properties:


There are three main components of a galaxy cluster. They are tabulated below: [ citation needed ]

Name of the componentsMass fractionDescription
Galaxies1%In optical observations, only galaxies are visible
Intergalactic gas in intracluster medium 9%Plasma between the galaxies at high temperature and emit x-ray radiation by thermal bremsstrahlung
Dark matter90%Most massive component but cannot be detected optically and is inferred through gravitational interactions


Galaxy clusters are categorized as type I, II, or III based on morphology. [5] [6]


The Laniakea supercluster with many galaxy clusters 07-Laniakea (LofE07240).png
The Laniakea supercluster with many galaxy clusters
Notable clusters
Virgo Cluster The nearest massive galaxy cluster
Norma Cluster The cluster at the heart of the Great Attractor
Bullet Cluster A cluster merger with the first observed separation between dark matter and normal matter
This lists some of the most notable clusters; for more clusters, see the list article.
Abell 2744 galaxy cluster – extremely distant galaxies revealed by gravitational lensing (16 October 2014). [7] [8]



See also

Related Research Articles

Galaxy groups and clusters Largest known gravitationally bound object in universe; aggregation of galaxies

Galaxy groups and clusters are the largest known gravitationally bound objects to have arisen thus far in the process of cosmic structure formation. They form the densest part of the large-scale structure of the Universe. In models for the gravitational formation of structure with cold dark matter, the smallest structures collapse first and eventually build the largest structures, clusters of galaxies. Clusters are then formed relatively recently between 10 billion years ago and now. Groups and clusters may contain ten to thousands of individual galaxies. The clusters themselves are often associated with larger, non-gravitationally bound, groups called superclusters.

Gravitational lens Light bending by mass between source and observer

A gravitational lens is a distribution of matter between a distant light source and an observer, that is capable of bending the light from the source as the light travels towards the observer. This effect is known as gravitational lensing, and the amount of bending is one of the predictions of Albert Einstein's general theory of relativity.

Abell 2218 Galaxy cluster in the constellation Draco

Abell 2218 is a cluster of galaxies about 2 billion light-years away in the constellation Draco.

Norma Cluster Galaxy cluster in the constellation Norma

The Norma Cluster (ACO 3627 or Abell 3627) is a rich cluster of galaxies located near the center of the Great Attractor; it is about 68 Mpc (222 Mly) distant. Although it is both nearby and bright, it is difficult to observe because it is located in the Zone of Avoidance, a region near the plane of the Milky Way. Consequently, the cluster is severely obscured by interstellar dust at optical wavelengths. Its mass is estimated to be on the order of 1015 solar masses.

Einstein Cross

The Einstein Cross is a gravitationally lensed quasar that sits directly behind ZW 2237+030, Huchra's Lens. Four images of the same distant quasar appear around a foreground galaxy due to strong gravitational lensing. This system was discovered by John Huchra and coworkers in 1985.

Coma Cluster Cluster of galaxies in the constellation Coma Berenices

The Coma Cluster is a large cluster of galaxies that contains over 1,000 identified galaxies. Along with the Leo Cluster, 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.

Interacting galaxy Galaxies whose gravitational fields result in the disturbance of one another.

Interacting galaxies are galaxies whose gravitational fields result in a disturbance of one another. An example of a minor interaction is a satellite galaxy disturbing the primary galaxy's spiral arms. An example of a major interaction is a galactic collision, which may lead to a galaxy merger.

Abell 1689 Galaxy cluster in the constellation Virgo

Abell 1689 is a galaxy cluster in the constellation Virgo nearly 2.2 billion light-years away.

A1689-zD1 Galaxy in the constellation Virgo

A1689-zD1 is a galaxy in the Virgo constellation cluster. It was a candidate for the most distant and therefore earliest-observed galaxy discovered as of February 2008, based on a photometric redshift.

Abell 370 Galaxy cluster in the constellation Cetus

Abell 370 is a galaxy cluster located approximately 4 billion light-years away from the Earth, in the constellation Cetus. Its core is made up of several hundred galaxies. It was catalogued by George Abell, and is the most distant of the clusters he catalogued.

Abell 2163

Abell 2163 is one of the richest and most distant of the clusters of galaxies found in the Abell catalogue. Its abell richness class is 2 and position is at a redshift z=0.2. Data from Chandra X-ray Observatory have shown that it is the hottest galaxy cluster in the Abell catalogue. It is also a merging cluster.

Abell 2744 Galaxy cluster in the constellation Sculptor

Abell 2744, nicknamed Pandora's Cluster, is a giant galaxy cluster resulting from the simultaneous pile-up of at least four separate, smaller galaxy clusters that took place over a span of 350 million years. The galaxies in the cluster make up less than five percent of its mass. The gas is so hot that it shines only in X-rays. Dark matter makes up around 75 percent of the cluster's mass.

El Gordo (galaxy cluster)

El Gordo is the largest distant galaxy cluster observed at its distance or beyond, as of 2011. As of 2014, it still holds the record for being the largest distant galaxy cluster to have been discovered with a mass of 3 quadrillion suns. It was found by NASA's Chandra X-ray Observatory, Atacama Cosmology Telescope - funded by National Science Foundation, and European Southern Observatory's Very Large Telescope.

MACS0647-JD The farthest known galaxy from the Earth in the constellation Camelopardalis

MACS0647-JD is a galaxy with a redshift of about z = 10.7, equivalent to a light travel distance of 13.26 billion light-years. If the distance estimate is correct, it formed about 427 million years after the Big Bang.

MACS J0416.1-2403 Galaxy cluster in the constellation Eridanus

MACS J0416.1-2403 is a cluster of galaxies at a redshift of z=0.397 with a mass 160 trillion times the mass of the Sun inside 200 kpc (650 kly). Its mass out to a radius of 950 kpc (3,100 kly) was measured as 1.15 × 1015 solar masses. The system was discovered during the Massive Cluster Survey, MACS. This cluster causes gravitational lensing of distant galaxies producing multiple images. In 2015, the galaxy cluster was announced as gravitationally lensing the most distant galaxy (z = 12). Based on the distribution of the multiple image copies, scientists have been able to deduce and map the distribution of dark matter.

MACS J1149 Lensed Star 1 Blue supergiant and most distant star from earth detected in the constellation Leo

MACS J1149 Lensed Star 1, also known as Icarus, is a blue supergiant star observed through a gravitational lens. It is the most distant individual star to have been detected so far, at approximately 14 billion light-years from Earth. Light from the star was emitted 4.8 billion years after the Big Bang. According to co-discoverer Patrick Kelly, the star is at least a hundred times more distant than the next-farthest non-supernova star observed, SDSS J1229+1122, and is the first magnified individual star seen.

SPT0615-JD Galaxy

SPT0615-JD is a dwarf galaxy situated within the constellation Pictor, and is the farthest galaxy ever imaged by means of gravitational lensing, as of 2018. Brett Salmon of the Space Telescope Science Institute in Baltimore was the lead scientist of the study of the galaxy.

RCS2 J2327 Extremely massive galaxy cluster

RCS2 J2327 is an extremely massive galaxy cluster. It is located approximately 6.4 billion light years away in the constellation of Pisces, thus making it one of the farthest clusters away from Earth. Recent studies have shown that the galaxy cluster has the mass of two quadrillion suns, making it the second most massive galaxy cluster. The galaxies are known to be distorted by gravitational lensing, which can have the ability to deflect distort, and amplify the light from the objects behind it. It can also be observed in strong lens, weak lens, and microlens and has 85% invisible dark matter.


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