Editing Galaxy cluster (section)

==Composition==
Galaxy clusters have three main components. Galaxies themselves only make up a small fraction of clusters, although they are the only component we can detect in the [[visible spectrum]]. The heated gas of the intracluster medium (ICM) has a peak temperature between 30 and 100 million degrees Celsius.<ref name=":0" /> Dark matter makes up the majority of the mass of galaxy clusters, but cannot be detected optically.<ref name="Kravtsov2012" /> 
{| class="wikitable"
|-
! Component
! Mass fraction
! Description
|-
| Galaxies
| 1%
| In optical observations, only galaxies are visible
|-
| Intergalactic gas in [[intracluster medium]]
| 9%
| Plasma between the galaxies at high temperature and emit x-ray radiation by thermal [[bremsstrahlung]]
|-
| Dark matter
| 90%
| Most massive component but cannot be detected optically and is inferred through gravitational interactions
|}