Galaxy group
A galaxy group
The Milky Way galaxy is part of a group of galaxies called the Local Group.[6]
Characteristics
Groups of galaxies are the smallest aggregates of galaxies. They typically contain no more than 50 galaxies in a diameter of 1 to 2
Groups are the most common structures of galaxies in the universe, accounting for at least 50% of the galaxies in the local universe. Groups have a mass range between those of the very large
Types
There are several subtypes of groups.
Compact groups
A compact group consists of a small number of galaxies, typically around five, in close proximity and relatively isolated from other galaxies and formations.[10] The first compact group to be discovered was Stephan's Quintet, found in 1877.[11] Stephan's Quintet is named for a compact group of four galaxies plus an unassociated foreground galaxy.[10] Astronomer Paul Hickson created a catalogue of such groups in 1982, the Hickson Compact Groups.[12]
Compact groups of galaxies readily show the effect of
Fossil groups
Fossil galaxy groups, fossil groups, or fossil clusters are believed to be the end-result of galaxy merging within a normal galaxy group, leaving behind the X-ray halo of the progenitor group. Galaxies within a group interact and merge. The physical process behind this galaxy-galaxy merger is
The closest fossil group to the Milky Way is NGC 6482, an elliptical galaxy at a distance of approximately 180 million light-years located in the constellation of Hercules.[14]
Proto-groups
Proto-groups are groups that are in the process of formation. They are the smaller form of protoclusters.[15] These contain galaxies and protogalaxies embedded in dark matter haloes that are in the process of fusing into group-formations of singular dark matter halos.[16]
List
Group | Notes | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Local Group | The group where the Milky Way, including the Earth, is located | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Stephan's Quintet | One of the most photogenic groups | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Robert's Quartet | Another very notable group | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Bullet Group | The merging group exhibits separation of dark matter from normal matter | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
This lists some of the most notable groups; for more groups, see the list article. |
See also
Notes
- 1022 mfor distance comparisons
References
- ^ "Hubble views a bizarre cosmic quartet". Retrieved 19 June 2015.
- ^ Bärbel Koribalski (2004). "The NGC 6221/15 Galaxy Group".
- ^ Hartmut Frommert & Christine Kronberg. "Groups and Clusters of Galaxies with Messier objects". SEDS.
- ^ "Object classification in SIMBAD". SIMBAD. November 2013.
- ISBN 9780521671866.
- ^ Mike Irwin. "The Local Group". Retrieved 2009-11-07.
- ^ UTK Physics Dept. "Groups of Galaxies". University of Tennessee, Knoxville. Retrieved September 27, 2012.
- S2CID 17865754. A80.
- ^ S2CID 1427929.
- ^ S2CID 18870169.
- .
- doi:10.1086/159838.
- ^ Dependency of halo concentration on mass, redshift and fossilness in Magneticum hydrodynamic simulations
- ^ An old galaxy group: Chandra X-ray observations of the nearby fossil group NGC 6482
- )
- S2CID 17700696. 109.)
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