 The primary galaxy in the cluster, it is one of the most luminous galaxies known in terms of X-ray emissions.NGC 6166 is a supermassive, type cD galaxy, with several smaller galaxies within its envelope.Suspected to have formed through a number of galaxy collisions, NGC 6166 has a large number of globular clusters (estimated as between 6,200 and 22,000 in 1996) orbiting the galaxy.