Unique torsional magnetic plasma waves have been discovered and observed on the Sun’s surface by an international team of researchers.
The team of researchers, led by Professor Róbert Erdélyi, head of the Solar Physics and Space Plasma Research Centre at the University of Sheffield, have confirmed the existence of highly elusive antisymmetric torsional waves, also known as torsional Alfvén waves after Hannes Alfvén who predicted Alfvén waves theoretically in 1947.
The waves have been recognised for their importance in many research areas, including neutrino physics, the physics of interstellar medium, their role in mechanisms of particle acceleration around supermassive black holes, nuclear fusion research and in a wide range of industrial applications
The energy carrying capability of Alfvén waves is of fundamental interest in solar and plasma-astrophysics, where the extreme heating of the solar and stellar atmospheres, up to a few million degrees, remains unexplained.
Professor Erdélyi, from the University of Sheffield, said: “This was truly fascinating and thrilling research. To successfully hunt the mysterious signatures of these most peculiar magnetic waves that are present in the 4th state of matter in our Universe is a rare opportunity.
“The international race is on to find torsional Alfvén waves in nature. This is a strategic research area for many funding agencies because of the capability of these magnetic waves to heat up plasma up to 30 million degrees. If we would fully understand how this heating takes place, we could copy it from nature and harvest free, green energy to save our planet. If we do not act now, it may soon be too late for all of us, given the level of energy needs in order to maintain the running of our high-tech society and our entire technosphere.
“We have worked as a team, and I enjoyed learning a lot from our early career scientists, Drs Marianna B. Korsós, Chris Nelson and Callum Boocock who all made very important contributions.”
The solar atmosphere is penetrated with magnetic fields that are observed in bunches, called solar magnetic flux tubes. In a uniform magnetic flux tube, Alfvén waves manifest as either axisymmetric or anti-symmetric torsional perturbations.
However, their incompressible nature makes them the most elusive type of wave in the Sun, and detecting their direct signature remained a challenge. It’s impossible to “see” these waves, only measure the perturbations in some special components of the magnetic and velocity fields.
Thanks to high spatial and temporal resolution spectropolarimetric observations of the solar atmosphere made by the IBIS instrument, it was not only possible to confirm the existence of the waves in solar magnetic flux tubes but also identify them as a mechanism to extract vast amounts of energy from the solar atmosphere.
In addition, state-of-the-art supporting numerical simulations were carried out to provide new insights into the excitation mechanisms of these peculiar magnetic waves.
Dr Chris Nelson, from the University of Sheffield, said: “The detection of torsional oscillations in the visible imprints of the magnetic field itself is a wonderful result. This work opens up a range of future researches that can really test our understanding of how frequent and important Alfvén waves are in the solar atmosphere. I look forward to making further progress over the next few years with the next generation of solar telescopes.”
The researchers have published their findings in the journal Nature Astronomy.
The team was led by Dr Róbert Erdélyi, Head of the Solar Physics and Space Plasma Research Centre (SP2RC) from the University of Sheffield’s School of Mathematic and Statistics and President-Curator of the Hungarian Solar Physics Foundation, and Dr Marco Stangalini of the Italian Space Agency.
The full UK team included Dr Chris Nelson from the University of Sheffield and Queen’s University Belfast, Dr Marianna Korsós from the University of Sheffield and Aberystwyth University and Drs Callum Boocock and David Tsiklauri from Queen Mary University London.
Dr Marco Stangalini: “In our study we do not only detect this elusive wave mode, but also find that it is very efficient in extracting a large amount of energy from the photosphere. This amount of energy is even larger than what needed to heat the solar corona so the question is now where does this energy go. This is a fundamental question that will be better addressed thanks to the availability of new data from exciting projects like Solar Orbiter and DKIST, which will provide a tomographic view of the solar atmosphere with unprecedented resolution.”
Dr Marianna Korsós: “The research was about to find direct evidence for the presence of purely magnetic waves that earned the most prestigious prize to Alfvén about 50 years ago for its prediction. This is a fantastic area of astronomy that develops rapidly thanks to the better and better detectors. I am very proud to be part of this collaboration as a young female researcher and have learnt a lot about this thrilling area of science.”