Once a black hole has formed, it can continue to grow by absorbing additional matter. Any black hole will continually absorb gas andinterstellar dust from its direct surroundings and omnipresent cosmic background radiation. This is the primary process through which supermassive black holes seem to have grown.A similar process has been suggested for the formation of intermediate-mass black holes in globular clusters.
Another possibility is for a black hole to merge with other objects such as stars or even other black holes. Although not necessary for growth, this is thought to have been important, especially for the early development of supermassive black holes, which could have formed from the coagulation of many smaller objects. The process has also been proposed as the origin of some intermediate-mass black holes.