Stars May 'Sing' Songs That We Can't Hear

Do stars "sing?" They just may be able to, according to new research. A chance discovery has revealed that stars may generate sound that we are unable to hear.

The scientists were examining the interaction of an ultra-intense laser with a plasma target. That's when they noticed something unexpected. The researchers realized 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.

Yet this sound wasn't audible by humans. It was generated at such a high frequency that even bats and dolphins wouldn't have been able to hear it. In fact, at nearly a trillion hertz it was close to the highest frequency possible in such a material.

"One of the few locations in nature where we believe this effect would occur is at the surface of stars," said John Pasley, one of the researchers, in a news release. "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."

The researchers detected the sound in the lab by using a technique that works similarly to a police speed camera. It allowed the scientists to accurately measure how fluid is moving at the point it is struck by the laser on timescales 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," said Alex Robinson, one of the researchers. "Similar situations could occur in plasma flowing around stars."

The findings are published in the journal Physical Review Letters.

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