Stars generate sounds on their surface in an unexpected way, according to new experimental evidence. Of course, as space is a vacuum it is impossible to hear sound in space, but the discovery reveals a new way that fluids can interact to produce a sound - one with an extremely high frequency. The discovery was made by a team of scientists including Dr John Pasley of the York Plasma Institute in the Department of Physics. A team of scientists that included York University made the discovery. They fired an ultra-intense laser on fluids in a laboratory. When they did this, the plasma in the fluid produced a sound wave. This process is thought to also be taking place in stars (sun pictured) They found that, when material - dust or gas from nearby - falls onto a star, it can produce an extremely high pitched sound in the plasma. Dr Pasley told MailOnline that the phenomenon is 'more common in younger stars' that are still accumulating material from their surroundings. It would be less common in more mature stars, like our sun. To make the finding, the team studied fluids in motion in a laboratory and found that, when plasma is hit with an ultra-intense laser, it produces some strange effects. Using a method not too dissimilar to how a speed camera works, they were able to observe how the fluid moves at the point it is struck. Often called the fourth state of matter, plasma is a state of matter where heat or another energy has been added to a gas. This makes many of its atoms release some, or all, of their electrons. The resultant electrically charged gas is said to be ‘ionised’, and when enough atoms are ionised, the gas is said to be a plasma. Interestingly, plasma is thought to make up more than 99 per cent of all matter in the universe. A trillionth of a second after the laser hits, plasma was found to flow quickly from areas of high density to low density. In so doing, the plasma between the regions of different density produces pressure pulses, or a sound wave. However, with a frequency of nearly a trillion hertz, the sound wave produced is six million times higher in frequency than anything that can be heard by a mammal. It is also almost the highest frequency possible in such a material. According to the scientists, a prime location for this rare event occurring is on the surface of stars. The process is thought to be taking place on stars like the sun, pictured, where plasma is in abundance. In fact, plasma is thought to make up 99 per cent of matter in the universe . ‘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 Dr Pasley. However, he noted that it would be difficult to directly observe this effect in stars, as the sound waves do not propagate into the space around the star. ‘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,’ added Dr Alex Robinson, from the Plasma Physics Group at the Science and Technology Facilities Council’s Central Laser Facility in Oxfordshire. ‘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, published in Physical Review Letters, was funded by the Engineering and Physical Sciences Research Council and the Tata Institute of Fundamental Research.
A team of scientists that included York University made the discovery . They fired an ultra-intense laser on fluids in a laboratory . When they did this, the plasma in the fluid produced a sound wave . This process is thought to also be taking place in stars . However, as space is a vacuum, you wouldn't hear anything if nearby .