Brightest cluster galaxy

A D- galaxy is a special type of giant elliptical galaxy. D- galaxies differ from normal elliptical galaxies by their huge diffuse halo, which gives them their name (" D" for " diffuse ").

The main D- galaxies can be found in the center of rich clusters of galaxies, where they often occur singly or in pairs and reach enormous sizes with radii up to 1 million light years. Such D- galaxies are called cD galaxies ("c" denotes the luminosity class ). The best known example of a galaxy cluster with a central pair of cD galaxies is relatively close to the Coma cluster with the two giant galaxies NGC 4874 and NGC 4884th They are orbiting at distances of up to about 20 Mpc of over 1000 individual star systems normal size, which however, enormous time needs. It is assumed that cD galaxies form by merging elliptical galaxies Giant with other galaxies in rich populated central region of the cluster ( " galactic cannibalism "). This is suggested by the facts out that many galaxies of this type have multiple cores, and that almost all of them are strong radio sources.

• Galaxy