Transcript: The event horizon is the imaginary surface of a black hole, the region from within which no object, no particle, no radiation, no wave, nothing can escape. Any star that collapses to this point essentially disappears from the universe, betraying its presence only by the force of gravity. The event horizon is not a physical surface or barrier. It is a mathematical surface and essentially acts as an information membrane. Information can flow into the event horizon but not out. Some theorists have speculated that a law of physics might potentially be violated by this because information is only passing in one direction and so can be lost from the universe. The properties of black holes within the event horizon are mysterious and are not even predicted by the theory of relativity.