Streams of dwarf galaxies (some are nearly dark) flow towards the centre around which galaxy groups are formed. The meetings of several dwarfs cause the formation of larger structures through merging of the smaller ones. This merging process heat the gases and generate x-rays. Therefore the  dynamics of the merging process can be best studied in x-rays.The merging  process around the centre may cause much turbulence and cause ejections of streams out from the central area. These hotter streams again return towards the centre after being cooled during their outward journey. These returned streams in turn participate in the creation of the larger galaxies in the group. Here is an example of this process of inflow and outflow in a galaxy group called Hcg 62 in Virgo.

Hallow of hot gases around the centre of Hcg 62

Coolig flow from south towards the centre of Hcg 62

Ejections from the centre of Hcg 62 towards north which return as cooling flow towards the centre again. The meetings of the hot and the cold flows create turbulence which add to the process of structure formation.