> Homepage > Print version > View previous issues OCTOBER 2009 News Business Energy Environment Science Communication Outreach International Sound of Silence Meet the President Another League Forward Vision Knight Star Sound of Silence World-first observation of an acoustic black hole By Georgina Johnson Dr Jeff Steinhauer Dr Jeff Steinhauer recently created an artificial black hole in his lab in the Faculty of Physics, paving the way for proving Stephen Hawkins’ prediction of radiation that is said to be emitted by black holes due to quantum effects. The groundbreaking finding was published on the physics Web site arXiv.org in June 2009. Steinhauer followed a suggestion made in 1981 by William Unruh of the University of British Columbia and created an analogue of a real black hole in the laboratory, using an extremely cold form of matter called a Bose-Einstein condensate. This analogue is dubbed a “dumb hole” because it swallows sound rather than light. The light-swallowing abilities of real black holes make them notoriously difficult to observe directly, though their gravitational effects on their surroundings can be seen. Some, such as those around which galaxies are believed to accrete, formed just after the beginning of the universe. A lot, though, are the result of huge stars collapsing in on themselves at the end of their lives. Whatever their origin, all black holes have an “event horizon,” within which gravity is so intense that nothing can escape. Steinhauer and his colleagues created a condensate out of a gas of rubidium atoms held in a magnetic trap. They then decompressed part of the gas, resulting in high-speed flow. They took photographs and used them to calculate both the speed of flow and the speed of sound within the condensate. Their data showed that the speed of part of the condensate exceeded the speed of sound, and they had therefore made an acoustic event horizon. Sound waves should be trapped in the supersonic region of the flow. “It’s like trying to swim slowly against a fast current,” says Steinhauer. “The sound waves are never able to escape the sonic event horizon and fall behind because the current is moving faster than the waves.” The next step is to look for sound waves emitted by the sonic black hole - the yet unobserved Hawking radiation, predicted by theoretical physicist Stephen Hawking. “This is about understanding the basic laws of physics,” Steinhauer said. “What this research is good for in day-to-day life I’m not sure, but we as humans want to understand how the universe works.” © 2009 Technion-Israel Institute of Technology, Division of Public Affairs and Resource Development All rights reserved. If you wish to use any text or graphics contained herein, please contact focus@tx.technion.ac.il