Although intergalactic space is very close to a total vacuum, surrounding and stretching between galaxies there is a rarefied plasma that is thought to possess a filamentary structure and that is slightly denser than the average density in the Universe. This material is called the intergalactic medium (IGM) and is mostly ionized hydrogen, i.e. a plasma consisting of equal numbers of electrons and protons. The IGM is thought to exist at a density of 10 to 100 times the average density of the Universe (10 to 100 hydrogen atoms per cubic meter). It reaches densities as high as 1000 times the average density of the Universe in rich clusters of galaxies.
Intracluster MediumLast Updated on 2009-03-27 at 14:36
The intracluster medium (ICM) is a hot ionized gas which fills the space between the galaxies in Galaxy Clusters (See Figure 1). The ICM is composed of gas which fell into the... More »
Galaxies: Morphology-Density RelationLast Updated on 2009-03-25 at 19:12
The morphology-density relation describes how different types of galaxies tend to be arranged in clusters.
In general, bulge-dominated early-type galaxies, Ellipticals and S0s,... More »