What is a galaxy cluster

Galaxy clusters

Galaxy clusters, Pile of fog, Collection of a few tens to several thousand galaxies. F. Zwicky was the first to notice in the 1930s that almost all galaxies are grouped in such clusters. It is therefore almost impossible that this is a matter of random, temporary inhomogeneities in the galaxy distribution. Galaxy clusters are held together by gravity and are, after the galaxy superclusters, the largest “structural components” in the universe. They reach diameters from one to over ten Mpc.

A distinction is made between regular and irregular clusters. Regular galaxy clusters are almost spherical with a strong concentration of galaxy density towards the center, where a huge elliptical galaxy often resides.

The Local Group, which contains the Milky Way and the Andromeda Nebula, is one of the small galaxy clusters.

The closest galaxy cluster is the Virgo Cluster (2500 galaxies, diameter: 3 Mpc) at a distance of 20 Mpc. The closest regular cluster of galaxies is the one 130 Mpc away Coma pile.

The masses of galaxy clusters can be calculated by observing the radial velocities of their members based on the virial theorem. It is also possible to estimate the mass of the luminous matter (mainly stars) from the number and luminosity of the galaxies. In most cases it exceeds Virial mass that of luminous matter by far (dark matter). In the seventies, the ~ 10th8 K discovered hot intergalactic matter, which can make up 10-40% of the virial mass in a galaxy cluster.