Hawking radiation

Hawking radiation is black body radiation which is emitted by black holes, due to quantum effects near the event horizon. It is named after the physicist Stephen Hawking, who provided a theoretical argument for its existence in 1974.

As a result of quantum fluctuations, particle-antiparticle pairs can appear from the vacuum of space near the event horizon of a black hole in which the net energy of the particles is zero due to the matter and antimatter nature of the particles. In normal conditions, particle-antiparticle pairs that appear due to the quantum fluctuations annihilate each other. But if one member of the pair falls beyond the event horizon of the black hole, the other particle will not have a sister with which to annihilate. The member that does not fall into the black hole is then emitted from the black hole as hawking radiation. The particle that falls into the black hole effectively has negative energy, meaning that it will subtract from the overall mass-energy content of the black hole. Thus, after enough time has passed, the black hole will evaporate from these negative particles, while seeming to emit positive ones. Hawking radiation reduces the mass and the energy of the black hole and is therefore also known as black hole evaporation. Because of this, black holes that lose more mass than they gain through other means are expected to shrink and ultimately vanish.

Hawking radiation is such a small effect that it has never been measured. Micro black holes (MBHs) are predicted to be larger net emitters of radiation than larger black holes (and should thus shrink and dissipate faster), but MBHs have yet to be observed.

Hawking Radiation Media

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  Picture of space infalling into a Schwarzschild black hole at the Newtonian escape speed. Outside/inside the horizon (red), the infalling speed is less/greater than the speed of light. At the event horizon, the infalling speed equals the speed of light. Credit: Andrew Hamilton, JILA