A black hole is a dense, compact object whose gravitational pull is so strong that – within a certain distance of it – nothing can escape, not even light.
Black holes are thought to result from the collapse of very massive stars at the ends of their evolution. The gravity is so strong because matter (the mass) has been squeezed into a tiny space.
This artist's impression depicts a rapidly spinning supermassive black hole surrounded by an accretion disc. The black hole is labeled, showing the anatomy of this fascinating object. ESO