Wednesday, March 25, 2015

Are the stars singing?

Image from Hubble Space Telescope 
Credit: NASA, ESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration

A chance discovery by a team of researchers has provided experimental evidence that stars may generate sound.

The study of fluids in motion – now known as hydrodynamics – goes back to the Egyptians, so it is not often that new discoveries are made. However when examining the interaction between an ultra-intense laser and a plasma target, the team, which included scientists from the Science and Technology Facilities Council’s (STFC) Central Laser Facility in Oxfordshire, the York Plasma Institute at the University of York, and the Tata Institute of Fundamental Research in Mumbai, India, noticed something unusual.

They realised 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.

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. He 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 sound generated was at such a high frequency that it would have left even bats and dolphins struggling. With 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 John Pasley from the York Plasma Institute said: “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.”

The technique used to observe the sound waves in the lab works very much like a police speed camera. It allows the scientists to very 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.

The research was funded by the Engineering and Physical Sciences Research Council and the Tata Institute of Fundamental Research. It is published in Physical Review Letters.


Marion O’Sullivan
STFC Press Office
Tel: 01235 445627
Mob: 07824 888990

Notes to Editors:  
  • The paper ‘Terahertz acoustics in hot dense laser-plasmas’ by Amitava Adak, A. P. L. Robinson, Prashant Kumar Singh, et al is published in Physical Review Letters.
  • The University of York was founded in 1963 with 230 students. It now has around16,000 students and more than 30 academic departments and research centres. It places equal emphasis on research and teaching. Students in every department -¬ both undergraduate and postgraduate - are taught and advised by leaders in their field. The University’s £750m campus investment represents one of the largest capital developments in UK Higher Education and provides new student accommodation, world-class research and teaching facilities, and embedded and stand-alone facilities for businesses. The University has a collegiate system in which most staff and all students are members of one of nine colleges.
  • For more information about York Plasma Institute
  • STFC’s Central Laser Facility is one of the world’s leading laser facilities, providing scientists from the UK and Europe with an unparalleled range of state-of-the-art laser technology. Its wide ranging applications include experiments in physics, chemistry and biology, accelerating subatomic particles to high energies, probing chemical reactions on the shortest timescales and studying biochemical and biophysical process critical to life itself.
  • The Engineering and Physical Sciences Research Council (EPSRC) is the UK’s main agency for funding research in engineering and the physical sciences. EPSRC invests around £800 million a year in research and postgraduate training, to help the nation handle the next generation of technological change. The areas covered range from information technology to structural engineering, and mathematics to materials science. This research forms the basis for future economic development in the UK and improvements for everyone’s health, lifestyle and culture. EPSRC works alongside other Research Councils with responsibility for other areas of research. The Research Councils work collectively on issues of common concern via Research Councils UK.