Galaxy group

[8] In the local universe, about half of the groups exhibit diffuse X-ray emissions from their intracluster media.

The diffuse X-ray emissions come from zones within the inner 10–50% of the groups' virial radius, generally 50–500 kpc.

[12] Compact groups of galaxies readily show the effect of dark matter, as the visible mass is greatly less than that needed to gravitationally hold the galaxies together in a bound group.

Fossil groups are thus an important laboratory for studying the formation and evolution of galaxies and the intragroup medium in an isolated system.

[9][10] This hypothesis is supported by studies of computer simulations of cosmological volumes.

[13] The closest fossil group to the Milky Way is NGC 6482, an elliptical galaxy at a distance of approximately 180 million light-years located in the constellation of Hercules.