Acoustic Black Holes

Acoustic black holes have been created artificially by physicists in an attempt to prove the existence of Hawking radiation.  The sound-trapping black holes are made "...by coaxing a material to move faster than the speed of sound in that medium, so that sound waves traveling within it cannot keep up, like fish swimming in a fast-moving stream. The sound is effectively trapped in the stream-like event horizon."

Creative Commons Image : 'Black Hole' by Eggybird on Flickr