A singularity that is not hidden by an event horizon. A singularity is a point of infinite density that theories predict should exist at the centre of a black hole. If the black hole is rotating (a Kerr black hole), then the area of the surrounding event horizon can be reduced to zero, leaving the singularity exposed to view. Some theorists have invoked the concept of cosmic censorship, which requires that all singularities be hidden behind event horizons at all times. If this is true, some unknown process must be operating in very rapidly rotating black holes to retain the event horizon.