Black hole, computer artwork. The black hole is shown as a gravitational well or depression in a grid representing spacetime. A black hole is formed when the core of a star collapses under its own weight, increasing its gravitational field to the point where nothing can escape, not even light. A star only forms a black hole if its mass is sufficiently large. The concepts of space-time and gravity as a distortion in spacetime caused by mass, come from Einstein's theories of Special and General Relativity.