Hawking radiation

Hawking radiation is how black holes decay, named for Stephen Hawking.

Space - that's all space, the void between galaxies and equally the space within and between the atoms of your body - is not empty. There is a constant creation/extinction of virtual particles (particle here can include energy as well). These particles come in particle-antiparticle pairs, which subsequently annihilate each other to respect energy conservation. This phenomenon is known as vacuum fluctuation, and it's all to do with quantum physics.

If such a fluctuation occurs at the event horizon of a black hole, it is possible during the very brief time that the pair exists that one might be pulled into the black hole while the other escapes. This second particle becomes real, while the former remains virtual and has to assume negative mass/energy due to the already mentioned energy conservation.


 * 1) There is thus a negative effect on the overall mass of the black hole.
 * 2) The smaller the black hole is, the faster it radiates.
 * 3) The temperature of the radiation emitted by this effect is, for small objects up to some hundred stellar masses, extremely low (< 1 x 10-9 Kelvin). More massive holes like those existing in the centers of galaxies will have even lower temperatures. Of course, that means a really low power output, thus naturally a very difficult time detecting said radiation.
 * 4) Tiny black holes will evaporate quickly. The less massive they are, the more energetic their radiation will be.
 * 5) All of the above means black holes will not begin to radiate until the temperature of the surrounding space (read: the cosmic microwave background, without matter infalling into them) are lower than the holes' one, something which will take quite a long time

For those who either are curious or are really bored and want to play with a calculator, the radiation temperature of a black hole is:


 * $$T_\mathrm{H} = \frac{\hbar c^3}{8 \pi G M k_\mathrm{B}} $$

This theory is not universally accepted because, as noted above, detection of Hawking radiation is way beyond our technologies but is a possible route whereby the universe will end as a low-temperature sea of photons.

Evaporation time
The time that it would take Hawking radiation to evaporate a black hole depends entirely on its mass:
 * $$t_{\operatorname{ev}} = \frac{5120 \pi G^2 M_0^{3}}{\hbar c^4} \approx 2.1\times10^{67}\,\text{years} \ \left(\frac{M}{M_\odot}\right)^3$$

Thus, a black hole with one Solar mass (2 x 1030 kg) would last for roughly 2 x 1067 years, while a black hole with a mass of 1 gram would last for 8 x 10-26 seconds.