Experiments reveal stars may generate sound waves

A chance discovery by a team of researchers, including a University of York scientist, has provided experimental evidence that stars might generate sound.

Scientists, including Dr John Pasley, of the York Plasma Institute in the Department of Physics at York, realised that in the trillionth of a second after the laser strikes, plasma flowed rapidly from areas of high density to more stagnant regions of low density, in such a way that it created something like a traffic jam. Plasma piled up at the interface between the high and low density regions, generating a series of pressure pulses: a sound wave.

However, the sound generated was at such a high frequency that it would have left even bats and dolphins struggling. With a frequency of nearly a trillion hertz, the sound generated was not only unexpected, but was also at close to the highest frequency possible in such a material; six million times higher than that which can be heard by any mammal!

Dr Pasley, who worked with scientists from the Tata Institute of Fundamental Research in Mumbai, India, and the Science and Technology Facilities Council's Central Laser Facility in Oxfordshire, said that one of the few locations in nature where they believe this effect would occur is the surface of stars.

The technique used to observe the sound waves in the laboratory works very much like a police speed camera. It allowed the scientists to accurately measure how fluid was moving at the point that was struck by the laser on timescales of less than a trillionth of a second. The study is published in Physical Review Letters.