Curvature of space by a black hole. A black hole is the collapsed remnant of a supermassive star. Its gravitation is so intense that its escape velocity is greater than the speed of light - so nothing may escape from it. This is often represented by a 'gravitational well' such as that seen here. Spacetime is represented on a two- dimensional grid, with gravitational potential represented by a third dimension. This illustrates the 'curvature' of spacetime by gravity - a concept introduced by Einstein in his celebrated 1915 paper on General Relativity.