## Black Holes are extremely cold

A black hole behaves as though its horizon has a temperature, and that temperature is inversely proportional to the hole's mass: T = (6 x 10^{-8})MHere M is expressed in units of solar masses (2 x 10

^{33}grams). The temperature is in degrees Kelvin, that is, degrees centigrade above absolute zero.This means that a hole recently formed by the gravitational collapse of a star (which has to have a mass larger than about 2 suns) has a temperature less than 3 x 10

^{-8}degrees centigrade above absolute zero.That's pretty damn cold.

A mass with a finite temperature radiates energy. Anything that radiates energy is also losing mass. Looking at the equation you can see that as the black hole loses mass, the emission of energy from the black hole increases and its temperature increases, and thus the rate of mass loss increases. As the mass of the black hole gets small, we have an unstable "runaway" effect.

The black hole gets hotter and hotter...

Which causes M to decrease rapidly...

Thus making the black hole even hotter.

When the hole is reduced to a fraction of the size of an atomic nucleus it will be trillions of degrees. The hole will burn up and eventually disappear!

The lifetime of a black hole is greater than the age of the universe.

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