Previously we have talked about the different galaxy types, and it got us thinking about structures that could be larger than the single galaxy? The answer is galaxy clusters and superclusters.
Galaxy Clusters
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. Until the discovery of galactic superclusters in the 1980s, these galactic clusters were thought to be the largest known gravitationally bound structures in the universe.
Galaxy clusters typically have the properties that include but not limited to:
- Containing anywhere from 100 to 1,000 galaxies, hot X-ray emitting gas and large amounts of dark matter.
- The distribution of the three components is approximately the same in the cluster.
- Total masses of 1014 to 1015 solar masses.
- Typical diameters of 2 to 10 Mpc
- The spread of velocities for the individual galaxies is about 800–1000 km/s.
The typical comports of galactic components is typically the same in roughly every cluster, which is shown in the table below.
| Name of the components | Mass fraction |
|---|---|
| Galaxies | 1% |
| Intergalactic gas in intracluster medium | 9% |
| Dark matter | 90% |
Galaxy Superclusters
First postulated by George Abell in 1958, a galactic supercluster is the largest-known structure of the cosmos. Made up of several smaller galaxy clusters or galaxy groups, the number of superclusters are estimated to be 10 million. Because of their large size and low density of superclusters means that they expand with the Hubble Expansion.
Because superclusters exist, this indicates that the distribution of galaxies in the Universe are not uniformly distributed. This is because most of the galaxies are drawn together in groups and clusters, with groups containing up to some dozens of galaxies and clusters up to several thousand galaxies. Interspersed among superclusters are large voids of space where few galaxies exist.
Although superclusters are supposed to be the largest structures in the universe, according to the Cosmological principle, larger structures have been observed in surveys, including the Sloan Great Wall.
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