Q&A: Black Holes

Q:
The temperature of a black hole is only a fraction of a degree above absolute zero. How is this possible when the black hole ingests everything within its grasp ? What happens to the matter and energy captured by the black hole ?

A:
The temperature of an object in thermal equilibrium is related to the rate at which object radiates energy divided by its area. As shown by Stephen Hawking and others, this relation can be applied to black holes if the area is taken to be the surface area described by the event horizon. The energy radiated by a black hole is for all practical purposes zero, so the temperature is very close to zero. An extremely small amount of energy is radiated by the Hawking process, but this is negligible for a stellar mass black hole or larger. The matter and energy captured by a black hole is trapped there forever, and the mass of the black hole increases.