Scientists may have discovered the "sound" of stars by observing fluid in motion.
A team of researchers observed the reaction of an ultra-intense laser with a plasma target, the University of York reported. They noticed that a trillionth of a second after the laser strikes, plasma flowed from regions of high density to those of lower density. This event caused plasma to build up at the interface between high and low density areas, generating a sound wave.
The sound was of a frequency of more than a trillion hertz, which is six million times higher than what can be heard by any mammal.
"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," said John Pasley, of the York Plasma Institute in the Department of Physics at York.
The technique used to observe this sound wave works similarly to a police speeding camera, allowing the researchers to analyze how the fluid moved when struck by the laser on a timescale of less than a trillionth of a second.
"It was initially hard to determine the origin of the acoustic signals, but our model produced results that compared [favorably] 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," said Alex Robinson from the Plasma Physics Group at STFC's Central Laser Facility.
The findings were published in a recent edition of the journal Physical Review Letters.
