text: Acoustic black holes were first theorized to be useful by William Unruh in 1981. However, the first black hole analogue was not created in a laboratory until 2009. It was created in a rubidium Bose–Einstein condensate using a technique called density inversion. This technique creates a flow by repelling the condensate with a potential minimum. The surface gravity and temperature of the sonic black hole were measured, but no attempt was made to detect Hawking radiation. However, the scientists who created it predicted that the experiment was suitable for detection and suggested a method by which it might be done by lasing the phonons. In 2014, stimulated Hawking radiation was reported in an analogue black-hole laser by the same researchers. Quantum, spontaneous Hawking radiation was observed later.
  A rotating sonic black hole was used in 2010 to give the first laboratory testing of superradiance, a process whereby energy is extracted from a black hole.