A team of researchers from University of York and Mumbai-based TIFR found evidence that stars may generate sound, in a chance discovery.
The study of fluids in motion or hydrodynamics dates back to the Egyptians but while examining the interaction of an ultra-intense laser with a plasma target, the team observed something unexpected.
Scientist 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 low density, as if it is due to a traffic jam.
Plasma piled up at the interface between the high and low density regions, generating a series of pressure pulses, which is a sound wave, said researchers.
Interestingly, the sound generated was at such a high frequency that even bats and dolphins would struggle to hear 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 jointly 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 it could occur at the surface of stars.
“One of the few locations in nature where we believe this effect would occur is at the surface of stars. When they are accumulating new material stars could generate sound in a very similar manner to that which we observed in the laboratory – so the stars might be singing – but, since sound cannot propagate through the vacuum of space, no-one can hear them,” he said.
The technique he used is similar to a police speed camera that allows the scientists to accurately measure how fluid is moving at the point that is struck by the laser on timescales of less than a trillionth of a second.
Dr Alex Robinson from the Plasma Physics Group at STFC’s Central Laser Facility developed a numerical model to generate acoustic waves for the experiment.
Robinson said, “It was initially hard to determine the origin of the acoustic signals, but our model produced results that compared favourably with the wavelength shifts observed in the experiment. This showed that we had discovered a new way of generating sound from fluid flows. Similar situations could occur in plasma flowing around stars.”
The research was published in Physical Review Letters.