Black hole, computer artwork. Black holes are regions of space in which the gravitational field is so strong that not even light can escape. Infalling matter is accelerated and heated as it falls into the hole, emitting high-energy X-rays. Black holes form from the collapsed core of a massive star at the end of its life. When all a massive star's fuel has been used up it can no longer support its own weight against gravity, and it collapses catastrophically. The collapse compresses the matter to extremely high density, increasing its gravitational field to the extent that nothing can escape.