Intermediate mass black hole (IMBH), composite of optical and Chandra X-ray telescope images. The IMBH is the large red dot at centre, in one of the spiral arms of the galaxy M74. It is an ultraluminous X-ray source (ULX). ULXs are unusual as they radiate 10 to 1000 times more power than stellar mass black holes. This ULX is thought to be a black hole with a mass of around 10,000 Suns. This is between stellar black holes at around ten solar masses, and black holes at the centres of galaxies, with millions of solar masses. IMBHs could form from the coalescence of several stellar black holes, or be the central black hole in a small galaxy captured by this larger one. This is a cropped version of R670/196.