Intracluster medium

The overlaid blue cloud illustrates the intracluster medium around the Spiderweb Galaxy, as seen when the universe was 3 billion years old

In astronomy, the intracluster medium (ICM) is the superheated plasma that permeates a galaxy cluster. The gas consists mainly of ionized hydrogen and helium and accounts for most of the baryonic material in galaxy clusters. The ICM is heated to temperatures on the order of 10 to 100 megakelvins, emitting strong X-ray radiation.