Researchers have confirmed the presence of magnetic plasma waves in the Sun's photosphere, catching them in action. Known as Alfven Waves, these fascinating waves were first predicted in 1947.
The Alfven Waves, named after Nobel Prize-winning scientist Hannes Alfvenfirst, had not been seen by astronomers in action when it was first predicted 50 years ago, until now.
Astronomers have finally detected the waves using observations of the Sun's photosphere, the lowest layer of its atmosphere, and the region that emits the light humans can see.
Alfven waves form when charged particles or ions oscillate in response to interactions between electrical currents and magnetic fields. Magnetic fields in the sun can bundle together, forming flux tubes that can drive the formation of Alven waves.
The waves are believed to manifest in one of two forms in solar magnetic flux tubes, either axisymmetric torsional perturbations-- where symmetric oscillations occur around the flux tube, or anti-symmetric-- where oscillations occur as two swirls rotating in opposite directions in the flux tube.
Despite previous theories, torsional Alfven waves have never been directly identified in the solar photosphere.
A team of researchers led by Dr. Marco Stangalini at the Italian Space Agency (ASI), with other scientists including Queen Mary’s Dr. David Tsiklauri and Ph.D. student Callum Boocock, used ESA's Imager on Board the Integral Satellite (IBIS) to monitor the Sun's photosphere.
The researchers also performed numerical simulations to explore the excitation mechanisms using a magnetohydrodynamic simulation designed by scientists from Queen Mary.
"What was amazing is that our idea that linearly polarized Alfven Wave driving at the bottom of a magnetic flux tube will result in the generation of torsional oscillations in the entire flux tube held true for a wide range of physical parameters. Both observations and simulations were signaling the discovery of Alfven waves," said Dr. David Tsiklauri, Visiting Senior Lecturer at Queen Mary’s School of Physics and Astronomy.
Callum Boocock, a Ph.D. student at Queen Mary’s School of Physics and Astronomy, explained, "The observations of torsional Alfven waves made by Marco and his team were remarkably similar to the behavior seen in our MHD simulations, demonstrating the importance of these simulations for discovering and explaining wave generation mechanisms."
The researchers hope to be able to use new opportunities by recently commissioned facilities, such as the Solar Orbiter satellite and the ground-based Daniel K. Inouye Solar Telescope (DKIST), to continue to study the relevance of Alfven Waves and potentially reveal the secrets of the Sun.
"Torsional oscillations within a magnetic pore in the solar photosphere" - Stangalini, M., et al. - Nature Astronomy - DOI: 10.1038/s41550-021-01354-8
Alfvén waves have proven to be important in a range of physical systems due to their ability to transport non-thermal energy over long distances in a magnetized plasma. This property is of specific interest in solar physics, where the extreme heating of the atmosphere of the Sun remains unexplained. In an inhomogeneous plasma such as a flux tube in the solar atmosphere, they manifest as incompressible torsional perturbations. However, despite evidence in the upper atmosphere, they have not been directly observed in the photosphere. Here, we report the detection of antiphase incompressible torsional oscillations observed in a magnetic pore in the photosphere by the Interferometric Bidimensional Spectropolarimeter. State-of-the-art numerical simulations suggest that a kink mode is a possible excitation mechanism of these waves. The excitation of torsional waves in photospheric magnetic structures can substantially contribute to the energy transport in the solar atmosphere and the acceleration of the solar wind, especially if such signatures will be ubiquitously detected in even smaller structures with the forthcoming next generation of solar telescopes.
Featured image credit: Alan Friedman
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