Physicists create 'black hole for sound' - space - 17 June 2009 - New Scientist

Description

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.

Quantum state

The materials physicists are focusing on are called Bose-Einstein condensates (BECs), a quantum state of matter where a clump of atoms behaves like a single atom.

Condensates have been made that move supersonically before, so physicists have likely created acoustic black holes in the process of working with BECs, says Eric Cornell of the University of Colorado at Boulder, who shared a 2001 Nobel Prize for the development of Bose-Einstein condensates.

But he says a new study by Jeff Steinhauer of the Technion-Israel Institute of Technology in Haifa and colleagues is the first documented experiment directly aimed at producing Hawking radiation in a BEC.

Supersonic flow

The team cooled 100,000 or so charged rubidium atoms to a few billionths of a degree above absolute zero and trapped them with a magnetic field. Using a laser, the researchers then created a well of electric potential that attracted the atoms and caused them to zip across the well faster than ...

Original URL

http://www.newscientist.com/article/dn17319-physicists-create-black-hole-for-sound.html?DCMP=OTC-rss&nsref=quantum-world

http://www.newscientist.com/article/dn17319-physicists-create-black-hole-for-sound.html?DCMP=OTC-rss&nsref=quantum-world