Evidence for a black hole in galaxy M87. False- colour optical image made by the Hubble Space Telescope of a spiral disc of hot gas in the core of galaxy M87, providing evidence for a black hole. In the right-hand image, a large optical jet is seen running toward top right. This is caused by emissions of high-speed electrons thought to come from a black hole. Spectroscopic measurements of the rotational velocity of the gas disc indicate a massive gravitational field in the core, far larger than may be explained by the density of stars in the centre. The black hole has a mass about 3 billion times that of the Sun.