Animation of a journey into a black hole. Black holes are regions of space that are so dense that their gravitational field is strong enough to prevent light from escaping. Stellar mass black holes are thought to form from the death of enormous stars, and black holes with millions of times that mass are thought to reside at the centre of most galaxies. Infalling matter is heated as it spirals into the hole in the form of an accretion disc, causing it to emit radiation. This is hotter and bluer the nearer the centre it is.