Q&A: Black Holes

Q:
What ultimately happens to black holes? Are they forever, or do they eventually transition into some other state of energy and/or matter?

A:
According to our current knowledge, black holes will eventually evaporate by a process called Hawking radiation (after Stephen Hawking). Eventually in this case means 10 to the 65th power years (1 followed by 65 zeroes) for a 10 solar mass black hole, and 10 to the 80th power years for a million solar mass black holes (the evaporation time goes as the cube of the mass). For comparison, the age of the universe is "only" about 15 billion years.

Hawking radiation occurs because empty space, or the vacuum, is not really empty. It is actually a sea of virtual particles of every type that pop into and out of existence for a very brief time. This is possible because according to the uncertainty principle of quantum mechanics, energy may always be borrowed from the vacuum, but it must be repaid quickly. The greater the amount borrowed, the quicker it must be repaid. For example, the energy to make an electron and its anti-particle, a positron -- virtual particles must be created in pairs must be repaid in one sextillionth of a second or to use the scientific term, one zeptosecond! Hawking showed that if a pair of virtual particles is created near a black hole, there is a chance that one of them will be sucked into the black hole before it is destroyed. In this event, its partner will escape into space, and a virtual particle will have become real. The energy for this came from the black hole, so the black hole slowly loses energy by this process.