The remarkable black hole radiation predicted 40 years ago by Stephen Hawking has never been observed. But an analogous phenomenon has been seen by Jeff Steinhauer (Technion–Israel Institute of Technology) in a Bose–Einstein condensate (BEC) of rubidium-87 atoms. In the analogue fluid system, sound plays the role that light does for a black hole, and a region in which the fluid flow exceeds the speed of sound substitutes for the light-trapping interior of the black hole (see also Physics Today, August 2005, page 19). To generate an analogue black hole horizon separating supersonic and subsonic flow, Steinhauer accelerated a portion of the BEC by illuminating it with a half-moon-shaped laser spot. Moreover, the potential Steinhauer used to confine his BEC created a second, inner horizon downstream of the black hole horizon, where the flow again became subsonic. The two horizons are indicated on the figure, which shows...

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