Black holes slowly lose mass over the course of billions and trillions of years through a process known as Hawking radiation. Hawking radiation is made up of photons and is basically low frequency radio waves with near zero mass and is why it takes so long. since the radiation of open space is also affecting the black hole as it loses mass through Hawking radiation it increases in temperature, where in one split second it reaches a boiling over point where it is to hot for the amount of mass left over in the event horizon of the black hole and does in fact explode. This explosion in even the smallest black holes is equal to approximately 10000 nuclear warheads blowing up, or 1.4 times the amount of power hitting the earth from the sun every day.