Hawking radiation

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This article is only a brief description of the subject and is not intended to give a full explanation.
Check out the "see also" or "references" sections, or Wikipedia's article for more detail.

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Hawking radiation is the means by which black holes decay. It is 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 subatomic particles (particle here can include energy as well). These particles are created in particle-antiparticle pairs, which subsequently annihilate each other. This is known as vacuum fluctuation and it's all to do with quantum physics.[1].

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 of them 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 conservation of energy.

  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).
  4. Tiny black holes will evaporate very fast.

This theory is not universally accepted[2] but is a possible route whereby the universe will end as a low temperature sea of photons.

Evaporation time[edit]

The time that it would take a black hole to completely evaporate via Hawking radiation depends entirely on its mass:

t_{\operatorname{ev}} = \frac{5120 \pi G^2 M_0^{3}}{\hbar c^4} \;

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

See also[edit]


  1. Hawking radiation Classically, black holes are black. Quantum mechanically, black holes radiate, with a radiation known as Hawking radiation, after the British physicist Stephen Hawking who first proposed it. (University standard article)
  2. Do black holes radiate? (Also University standard article)