Thermal Hawking radiation

In 1974, Stephen Hawking showed that quantum effects mean black holes are not completely black but actually emit a type of radiation, now known as Hawking radiation. It is thought that the entropy of black holes and the Hawking radiation should have the same temperature, given by the surface gravity. Astrophysical observations of such effects may not be possible but the physics of Hawking radiation should be measurable in analogous systems. Using ultracold atoms to create an analogue black hole for sound, Jeff Steinhauer and colleagues now experimentally measure the correlations between the Hawking radiation inside and outside of an analogue black hole and show that it has a thermal spectrum, with a temperature given by the surface gravity, as predicted by Hawking’s theory.