Galaxy clusters are large collections of galaxies. They consist of hundreds of galaxies and galaxy groups, bound together by gravity. Galaxy clusters are much larger than galaxy groups, like our Local Group.
Still larger than galaxy clusters are superclusters. 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 (Hubble's law).
Galaxy clusters typically have the following properties.
- They contain 50 to 1,000 galaxies, hot X-ray emitting gas and large amounts of dark matter. Details are described in the "Composition" section.
- The distribution of these three components is approximately the same in the cluster.
- They have total masses of 1014 to 1015 solar masses.
- They typically have a diameter from 2 to 10 megaparsecs.
- The spread of velocities for the individual galaxies is about 800–1000 km/s.
- The intracluster medium or ICM has gas between the galaxies with a temperature of 7-9 keV.
There are three main components of a galaxy cluster. They are:
|Name of the components||Mass fraction||Description|
|Galaxies||1%||In optical observations only galaxies are visible|
|Gas between galaxies, inside the cluster||9%||Plasma between the galaxies at high temperature – emit x-ray radiation|
|Dark matter||90%||Most massive component, cannot be seen, inferred by gravitational interactions|
Scale of thingsEdit
Where ">" means "contains":
- "The most distant mature galaxy cluster". ESO Science Release. ESO. Retrieved 9 March 2011.
- "Hubble pinpoints furthest protocluster of galaxies ever Seen". ESA/Hubble Press Release. Retrieved 13 January 2012.