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 (since we don't see it), collision-less (or it would have been slowed, like the gas) 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 (ClG 0024+16, ZwCl 0024+1652) 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.SIMBAD, "ClG 0024+17"

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 ("the fat one") is the biggest cluster found in the distant universe (at its distance and beyond), 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.NASA, "El Gordo Galaxy Cluster", 10 January 2012 (accessed 7 July 2012) 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.ESO, "A Galactic Crash Investigation", 22 June 2011 (accessed 7 July 2012)

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 (author of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing") 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.Saratoga Skies, "NGC 7331 (Deer Lick Group and Stephan's Quintet)", Jim Solomon (accessed 7 May 2009) 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 (Stephan's Quartet) 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 (1923–2008), 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 Group5 Apart from the Milky Way, only 4 galaxies are visible to the naked eye.Centaurus A/M83 Group2The 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 Group1 Only Bode's Galaxy (M81, NGC 3031) is visible to the naked eye.SEDS, Messier 81

No galaxy cluster is visible to the unaided eye.

Firsts

First discovered Name Date Notes Galaxy cluster Virgo Cluster1784 Discovered by Charles Messier. Galaxy group Compact group The four brightest members of Stephan's Quintet1877 Discovered by Edouard Stephan. Proto-cluster Double galaxy Magellanic Cloudsantiquity

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 distance: z= 0.451 LX-ray = 6.0 ± 0.1 × 1045 erg/s temperature: kT = 10.0 ± 0.3 keV

Closest groups

+ Galaxy groups closer than the Virgo Cluster Galaxy group Distance Redshift (z) Recession velocity (km/s) Notes Local Group - - - Our Galaxy, the Milky Way, belongs to the Local Group. LGG 104 (IC 342/Maffei Group, IC 342 / Maffei 1 Group, IC 342 Maffei 1-2 Group) 0.000868 The IC 342/Maffei Group contains two subgroups, the IC 342 subgroup (IC 342 Group) and the Maffei 1 subgroup (Maffei subgroup, Maffei 1 Group, Maffei Group). M81 Group (NGC 3031 Group) 0.001115 Hayden Planetarium, Galaxy Clusters and Superclusters Centaurus A/M83 Group (Centaurus A Group, M83 Group) 0.000999 The Centaurus A/M83 Group contains two subgroups, the Centaurus A subgroup (Centaurus A Group, NGC 5128 Group, LGG 344) and the M83 subgroup (M83 Group, NGC 5236 Group, LGG 355). Sculptor Group (South Polar Group) Canes Venatici Group (Canes Venatici I Group, Canes I Group, M94 Group, NGC 4736 Group, LGG 291) 0.001612 NGC 1023 Group (LGG 70) 0.002926 M101 Group (NGC 5457 Group, LGG 371) 0.001288 NGC 2997 Group (LGG 180) 0.002615 Canes Venatici II Group (Canes II Group) M51 Group (NGC 5194 Group, LGG 347) 0.001850 Leo Triplet (M66 Group, NGC 3627 Group, LGG 231) 0.002207 Leo Group (Leo I Group, M96 Group, NGC 3379 Group, LGG 217) 0.002267 Draco Group LGG 396 (NGC 5866 Group, NGC 5907 Group) 0.003020 Ursa Major Group (Ursa Major I Group, M109 Group, NGC 3992 Group, NGC 3726 Group, LGG 258) 0.003388 Mly represents millions of light-years, a measure of distance. Mpc represents millions of parsecs, a measure of distance (1 Mpc = 3.26 Mly). z represents redshift, a measure of recessional velocity and inferred distance due to cosmological expansion. In this very nearby context, however, the observed redshift and recessional velocity are due to the Doppler shifting of the light. Distances are measured from Earth, with Earth being at zero.

Closest clusters

+ Closest clusters Galaxy cluster Distance Redshift (z) Recession velocity (km/s) Notes Virgo Cluster 0.0038 The Virgo Cluster is at the core of the Virgo Supercluster. The Local Group is a member of the supercluster, but not the cluster.Hayden Planetarium, The 2MASS Galaxies Fornax Cluster (Abell S 373, AM 0336-353, MCL 52) 0.0046 Antlia Cluster (Abell S 636) 0.0087 Also called the Antlia Group. Centaurus Cluster (Abell 3526, Cl 1247-4102) 52.4 Mpc 0.0110 Hydra Cluster (Hydra I Cluster, Abell 1060, Cl 1034-2716) 58.3 Mpc 0.0114 Mly represents millions of light-years, a measure of distance. Mpc represents millions of parsecs, a measure of distance. z represents redshift, a measure of recessional velocity and inferred distance due to cosmological expansion. Distances are measured from Earth, with Earth being at zero.

Farthest clusters

+ Farthest clusters Galaxy cluster Distance Notes No entries yet Mly represents millions of light-years, a measure of distance. Mpc represents millions of parsecs, a measure of distance. z represents redshift, a measure of recessional velocity and inferred distance due to cosmological expansion. Distances are measured from Earth, with Earth being at zero.