Black holes form after supermassive stars (> 10 solar masses) explode as Type II supernovae. The remaining cores of these stars range from 2- 103 solar masses. Nothing is strong enough to hold the remaining mass against the force of gravity and the dying supermassive stars collapse into black holes. Nothing escapes from black holes, not even light; thus, the escape velocity of black holes is the speed of light. Since nothing can travel faster than the speed of light, nothing can escape. Matter that disappears from black holes loses contact with the rest of the Universe. Black holes are a consequence of Einstein’s theory of gravity, or General Relativity.