X-ray sources (red) in the spiral galaxy M74, composite of optical and Chandra X-ray telescope images. The sources are mostly black holes. The largest source, at upper left, is designated an ultraluminous X-ray source (ULX). This unusual source is thought to be a black hole with a mass of around 10,000 Suns. This lies in between the stellar mass black holes, at around ten solar masses, and the black holes at the centres of galaxies, with millions of solar masses. It is thought that such intermediate mass black holes form from the coalescence of stellar black holes, or are the cores of small galaxies. M74 lies some 32 million light years from Earth in the constellation Pisces. Image R670/195 is a crop centred on the ULX.