|I have read about how black holes can emit X-rays and radiation. If they absorb light, why do they emit these other things? — BA, Fairbury, IL
A black hole is surrounded by an imaginary surface called the event horizon. Nothing at all can escape from within this surface-not light, not X-rays...nothing! However, as matter falls into the black hole, and before it reaches the event horizon, the matter can emit any type of radiation it likes. The X-rays and radiation emitted "from a black hole" are actually coming from the area surrounding the event horizon, not from within that surface. As matter pours into a black hole, it often heats up so hot that it emits incredible amounts of radiation of all types so that black holes appear as very bright objects.