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.
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.