List of galaxy groups and clusters
This article lists some galaxy groups and galaxy clusters.
Defining the limits of galaxy clusters is imprecise as many clusters are still forming. In particular, clusters close to the Milky Way tend to be classified as galaxy clusters even when they are much smaller than more distant clusters.
Clusters exhibiting strong evidence of dark matter
Some clusters exhibiting strong evidence of dark matter.| Galaxy cluster | Notes |
| Bullet Cluster | In this collision between two clusters of galaxies, the stars pass between each other unhindered, while the hot, diffuse gas experiences friction and is left behind between the clusters. The gas dominates the visible mass budget of the clusters, being several times more massive than all the stars. Yet the regions with the stars show more gravitational lensing than the gas region, indicating that they are more massive than the gas. Some dark, collision-less matter is inferred to be present to account for the extra lensing around otherwise low-mass regions. |
| Abell 520 | This is actually a collision between two galaxy clusters. The galaxies and the dark matter seems to have separated out into separate dark and light cores. |
| Abell 2142 | A collision between two massive, X-ray luminous galaxy clusters. |
| Cl 0024+17 | This is a recently coalesced merger of galaxy clusters, which has resulted in a ring of dark matter around the galaxies, yet to be redistributed. |
Named groups and clusters
This is a list of galaxy groups and clusters that are well known by something other than an entry in a catalog or list, or a set of coordinates, or a systematic designation.Clusters
| Galaxy cluster | Origin of name | Notes |
| Bullet Cluster | The cluster is named for the merger of two clusters colliding like a bullet. | Also has a systematic designation of 1E 0657-56 |
| El Gordo | Named for its size, El Gordo is the biggest cluster found in the distant universe, at the time of discovery in 2011, with a mass of 3 quadrillion suns. The second most massive galaxy cluster next to El Gordo is RCS2 J2327, a galaxy cluster with the mass of 2 quadrillion suns. | Also has a systematic designation of ACT-CL J0102-4915. |
| Musket Ball Cluster | Named in comparison to the Bullet Cluster, as this one is older and slower galaxy cluster merger than the Bullet Cluster. | Also has a systematic designation of DLSCL J0916.2+2951. |
| Pandora's Cluster | Named because the cluster resulted from a collision of clusters, which resulted in many different and strange phenomena. | Also has a catalogue entry of Abell 2744. |
Groups
| Galaxy group | Origin of name | Notes |
| Local Group | The galaxy group that includes the Milky Way. | |
| Bullet Group | Named in comparison with the Bullet Cluster, being of similar formation, except smaller. | Also has a systematic catalogue name SL2S J08544-0121. As of 2014, it was the lowest mass object that showed separation between the concentrations of dark matter and baryonic matter in the object. |
| Burbidge Chain | ||
| Copeland Septet | Discovered by British astronomer Ralph Copeland in 1874. | |
| Deer Lick Group | Coined by Tom Lorenzin to honor Deer Lick Gap in the mountains of North Carolina, from which he had especially fine views of the galaxy group. | Also referred to as the NGC 7331 Group, after the brightest member of the group. |
| Leo Triplet | Named for the fact it contains only three galaxies. | This small group of galaxies lies in the constellation Leo. |
| Markarian's Chain | This stretch of galaxies forms part of the Virgo Cluster. | |
| Robert's Quartet | It was named by Halton Arp and Barry F. Madore, who compiled A Catalogue of Southern Peculiar Galaxies and Associations in 1987. | This compact group of galaxies lies 160 million light-years away in the Phoenix constellation. |
| Seyfert's Sextet | Named after its discoverer, Carl Seyfert. At the time it appeared to contain six external nebulae. It is also called the NGC 6027 Sextet, after its brightest member. | There are actually only five galaxies in the sextet, and only four galaxies in the compact group. One of the galaxies is an ungravitationally bound background object. The other "galaxy" is instead an extension of the interacting system — a tidal stream caused by the merger. The group is, therefore, more properly called HCG 79; the name refers to the visual collection and not the group. HCG 79 lies 190 million light-years away in the Serpens Caput constellation. |
| Stephan's Quintet | Named after its discoverer, Édouard Stephan. | There are actually only four galaxies in the compact group, the other galaxy is a foreground galaxy. The group is therefore more properly called HCG 92, because the name refers to a visual collection and not a group. Thus, the real group is also called Stephan's Quartet. |
| Wild's Triplet | Named after the British-born and Australia-based astronomer Paul Wild, who studied the trio in the early 1950s. | |
| Zwicky's Triplet |
The major nearby groups and clusters are generally named after the constellation they lie in. Many groups are named after the leading galaxy in the group. This represents an ad hoc systematic naming system.
Groups and clusters visible to the unaided eye
The Local Group contains the largest number of visible galaxies with the naked eye. However, its galaxies are not visually grouped together in the sky, except for the two Magellanic Clouds. The IC342/Maffei Group, the nearest galaxy group, would be visible by the naked eye if it were not obscured by the stars and dust clouds in the Milky Way's spiral arms.| Galaxy group | Visible galaxies | Notes |
| Local Group | 5 | Apart from the Milky Way, only 4 galaxies are visible to the naked eye. |
| Centaurus A/M83 Group | 2 | The Centaurus A galaxy has been spotted with the naked eye by Stephen James O'Meara and M83 has also reportedly been seen with the naked eye. |
| M81 Group | 1 | Only Bode's Galaxy is visible to the naked eye. |
- No galaxy cluster is visible to the unaided eye.
Firsts
| First discovered | Name | Date | Notes |
| Galaxy cluster | Virgo Cluster | 1784 | Discovered by Charles Messier. |
| Galaxy group | |||
| Compact group | The four brightest members of Stephan's Quintet | 1877 | Discovered by Edouard Stephan. |
| Proto-cluster | |||
| Double galaxy | Magellanic Clouds | antiquity |
Extremes
| Title | Name | Data | Notes | time |
| Most distant galaxy cluster | CL J1001+0220 | redshift z=2.506 | Announced August 2016. | |
| Nearest galaxy cluster | Virgo Cluster | The Virgo Cluster is at the core of the Virgo Supercluster. The Local Group is a member of the supercluster, but not the cluster. | ||
| Most distant galaxy group | ||||
| Nearest galaxy group | Local Group | 0 distance | This is the galaxy group that our galaxy belongs to. | |
| Nearest neighbouring galaxy group | IC 342/Maffei Group | |||
| Most distant proto-cluster | A2744z7p9OD | z=7.88 | ||
| Nearest proto-cluster | ||||
| Most distant massive proto-cluster | z66OD | z=6.585 | At time of discovery in 2019, the object had 12 members, including Himiko. | |
| Least massive galaxy group | ||||
| Most massive galaxy cluster | RX J1347.5-1145 | mass= 2.0 ± 0.4 × 1015 MSun |
|
Farthest clusters
- In 2003 RDCS 1252-29 at z=1.237, was found to be the most distant rich cluster, which lasted until 2005.
- In 2000, a cluster was announced in the field of quasar QSO 1213-0017 at z=1.31
- In 1999, cluster RDCS J0849+4452 was found at z=1.261
- In 1995 and 2001, the cluster around 3C 294 was announced, at z=1.786
- In 1992, observations of the field of cluster Cl 0939+4713 found what appears to be a background cluster near a quasar, also in the background. The quasar was measured at z=2.055 and it was assumed that the cluster would be as well.
- In 1975, 3C 123 and its galaxy cluster was incorrectly determined to lie at z=0.637
- In 1958, cluster Cl 0024+1654 and Cl 1447+2619 were estimated to have redshifts of z=0.29 and z=0.35 respectively. However, they were not spectroscopically determined.
Farthest protoclusters
- In 2002, a very large, very rich protocluster, or the most distant protosupercluster was found in the field of galaxy cluster MS 1512+36, around the gravitationally lensed galaxy MS 1512-cB58, at z=2.724
False clusters
Sometimes clusters are put forward that are not genuine clusters or superclusters. Through the researching of member positions, distances, peculiar velocities, and binding mass, former clusters are sometimes found to be the product of a chance line-of-sight superposition.| Former cluster | Notes |
| Cancer Cluster | The Cancer Cluster was found to be a random assortment of galaxy groups, and not a true cluster. |
| Coma-Virgo Cloud | The early identification of the Coma-Virgo Cloud of Nebulae was actually a mistaken identification due to the superposition of the Virgo Supercluster and Coma Supercluster, and not a Coma-Virgo Supercluster |