Physicists create 'black hole for sound' - space - 17 June 2009 - New Scientist:
"An artificial black hole that traps sound instead of light has been created in an attempt to detect theoretical Hawking radiation. The radiation, proposed by physicist Stephen Hawking more than 30 years ago, causes black holes to evaporate over time.
Astrophysical black holes are created when matter becomes so dense that it collapses to a point called a singularity. The black hole's gravity is so great that nothing – not even light – can escape from a boundary around it called an event horizon.
But physicists have also been developing 'black holes' for sound. They do this by coaxing a material to move faster than the speed of sound in that medium, so that sound waves travelling within it cannot keep up, like fish swimming in a fast-moving stream. The sound is effectively trapped in the stream-like event horizon."
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