Hawking Radiation
Hawking Radiation theory predicts that black holes may radiate energy. This effect has never been detected and Hawking Radiation has yet to be confirmed nor disproved.
Virtual particle pairs are constantly created in the vacuum of space (particle/anti-particle pairs that exist for an instant, borrowing energy from the vacuum of space, then mutually annihilate, returning the borrowed energy and leaving no net energy change).
However, if a particle/anti-particle pair is created at the event horizon of a black hole, with one particle just outside the event horizon and one particle just inside the event horizon, then the particle and anti-particle virtual pair might be separated, pulled apart to become real, with one falling into the black hole and one escaping. In order for a particle to escape from just outside the event horizon of a black hole, the particle (or anti-particle) may need to be a photon of light (or other particle that only travels at the speed of light) with speed c in the direction exactly opposite the pull of the black hole, and the particles must fail to annihilate, and fail to return the borrowed energy that created them. (Unknown if the direction of escape is important for virtual particles escaping micro black holes, as the size of virtual pairs may dwarf micro black hole distances).
Hawking Radiation theory predicts that if one virtual particle is captured by a black hole and one virtual particle escapes the black hole, then the universe would gain energy (one new virtual particle) so the black hole must somehow lose energy to balance the equation. Hawking theory assumes that the vacuum of space contains no energy, so the only possible source of the new energy is the the black hole. (However, assuming the vacuum of space is void of energy is counter to estimations that vacuum energy may contain at least 10-9 or up to 10113 Joules per cubic meter.[3][4]).
It may also be possible that black holes might capture both virtual particles without mutual annihilation (or infinitely delayed annihilation as time approaches a stop as the particles approach the center of mass of the black hole as General Relativity theory implies) or that all virtual particles mutually annihilate at the event horizon of black holes as they do in empty space, with perhaps no net energy change to the black hole.
Conclusion: Unknown if black holes actually radiate, and unknown if the energy source of this radiation would be the vacuum of space or the black hole itself, and unknown if this would cause black holes to shrink or to grow (virtual particle activity near black holes may be a mechanism of transferring energy from the vacuum of space to add to the mass of black holes).
[1] http://en.wikipedia.org/wiki/Vacuum_energy
the vacuum energy in a cubic meter of free space has been estimated to be 10−9 Joules.[2]
[2] Sean Carroll, Sr Research Associate - Physics, California Institute of Technology, June 22, 2006C-SPAN broadcast of Cosmology at Yearly Kos Science Panel, Part 1
[3] Peter W. Milonni - "The Quantum Vacuum"
Jump up[4] de la Pena and Cetto "The Quantum Dice: An Introduction to Stochastic Electrodynamics"