This supercomputer simulation shows one of the most violent events in the universe: a pair of neutron stars colliding, merging and forming a black hole. A neutron star is the compressed core left behind when a star born with between eight and 30 times the sun's mass explodes as a supernova. Neutron stars pack about 1.5 times the mass of the sun (equivalent to about half a million Earths) into a ball just 12 miles (20 km) across. As two such stars spiral toward each other, intense tides begin to deform them, possibly cracking their crusts. Tidal forces overwhelm and shatter the lesser star. Its superdense contents erupt into the system and curl a spiral arm of incredibly hot material. The more massive star accumulates too much mass to support it against gravity and collapses, and a new black hole is born.