A supergiant elliptical galaxy found at the centre of some rich clusters of galaxies. They are an extreme type of D galaxy. Their surface brightness falls off much more slowly with radius than for most elliptical galaxies, and they show an extensive faint halo of stars. They are among the most luminous of all galaxies, with luminosities up to about 2 × 1012 Suns, and they may have double or multiple nuclei. The evolution of cD galaxies may involve accretion of gas from the cluster and galaxy cannibalism.
Subjects: Astronomy and Astrophysics.