Scientists Say: Event horizon

Event horizon (noun, “Ee-VENT hur-AYE-zon”)

An event horizon is a boundary surrounding a black hole. Beyond this boundary, nothing — not matter, energy or any kind of information — can escape.

A black hole is an ultradense object with extremely strong gravity, which draws in matter and energy around it. The speed that something needs to escape an object’s gravity is called the escape velocity. (Something has to blast off Earth at about 11 kilometers per second or 7 miles per second, for instance, to escape into space.) But at a certain point around a black hole, matter or energy would have to travel faster than the speed of light to escape. A...