I remember reading about Hawking Radiation in a Brief History of Time. If I understood properly, owing to Quantum Mechanics, pairs of matter and anti-matter sub-particles would spontaneously appear outside the event horizon of a black hole. Sometimes the anti-matter sub-particle would enter the black hole and annihilate a little bit of it. Other times the anti-matter sub-particle would escape the event horizon but annihilate the first bit of matter it came across, releasing a lot of energy. Eventually the black hole would evaporate into space.
It's mind-boggling to think how long that would take, considering the size of the black holes at the centres of galaxies. It reminds me of those scare stories Roman Catholic priests used to tell about how if there was a mountain the size of the sun, and if every thousand years a bird would brush it with its wing, the mountain would be worn away before sinners stopped roasting in hell.