Ever wondered what kind of sound a star makes? Do stars even make sounds in the first place? Researchers clue you in as a chance discovery offers experimental evidence supporting sound generated by stars.
Hydrodynamics studies fluids in motion. It is not common for the field to have discoveries but researchers examining how an ultra-intense laser interacts with a target made of plasma were able to observe something unexpected, realizing that in the trillionth of a second after laser hits plasma, it flows rapidly from high-density areas to lower-density stagnant regions.
The way the plasma moved created something akin to heavy traffic in a busy intersection, with plasma piling up at points where regions of varying densities meet. The pile up creates pressure pulses and when plotted in a series, the pulses make up sound waves.
Unfortunately, generated sound featured such high frequencies that it cannot be heard. At almost a trillion hertz, the generated sound was not only surprising to researchers but was the highest frequency possible for plasma. A trillion hertz is higher by about six million fold compared to what mammals can hear! Even bats will have a hard time picking it up!
John Pasley from the York Plasma Institute said that one location that will make it possible for sound to be produced this way would be a star's surface.
He explained that when stars accumulate new material, sound could be generated in a manner very similar to what was observed by the researchers. But because sound cannot be propagated through vacuum, they cannot be heard.
The method researchers used for observing sound waves in the lab works similarly to speed cameras policemen use, accurately measuring the rate at which fluid will move after it is hit by a laser beam.
It was initially difficult to capture where acoustic signals were originating from. However, thanks to the numerical model developed by Alex Robinson of the Central Laser Facility's Plasma Physics Group, the researchers were able to gather enough information that could be compared with wavelength shifts. Robinson's work led the team to the chance discovery that sound may be generated through fluid flows and the method is highly similar to how plasma flows around stars.
The study received funding support from the Tata Institute of Fundamental Research and the Engineering and Physical Sciences Research Council. Its results were detailed in the journal Physical Review Letters.
Photo: Tom Hall | Flickr
