Spontaneous Hawking radiation in a sonic black hole

Stephen Hawking predicted that black holes should radiate, but observation of this Hawking radiation from a real astrophysical black hole seems unlikely, since the predicted temperature of the radiation is extremely low. Bill Unruh asserted that Hawking radiation might be observable in a sonic black hole, in which sound plays the role of light.

We make such an observation in a sonic black hole formed from a Bose-Einstein condensate. We confirm that the Hawking radiation is spontaneous, thermal, and stationary. Furthermore, we follow the time evolution of the Hawking radiation, and compare and contrast it with the predictions for real black holes. We observe the ramp up of the Hawking radiation, similar to a real black hole.

The spontaneous Hawking radiation ends, and stimulated Hawking radiation begins, when the sonic black hole forms an inner horizon in addition to the event horizon.