The morphology density relation – an observationally determined relationship between galaxy types and the environments in which they are located – suggests that star formation is suppressed when galaxies enter high density environments such as galaxy clusters. Although this suppression of star formation is not well understood, galaxy harassment and ram pressure stripping have been proposed as two processes through which it could occur.
Galaxy strangulation provides yet another process through which galaxies in clusters may lose their gas. As the galaxies fall into the cluster environment for the first time, the gravitational potential of the cluster (and its dark matter halo) create tidal effects that enable the gas contained within the galaxies to escape. As the gas is lost to the intra-cluster medium, the amount available to produce stars inside the galaxy gradually falls, and eventually, star formation within the galaxy will cease. In other words, star formation in the galaxy has died for want of gas – the galaxy has been strangled.