For the first time astronomers have observed waves of magnetic energy, known as Alfvén waves, in the photosphere of the sun. This discovery may help explain why the solar corona is so much hotter than the surface.
The sun is made of plasma, and like any plasma it should support Alfvén waves. These are waves in a plasma where the ions move in response to tension from a magnetic field. First predicted over 50 years ago, astronomers had until now had been unable to see them in the sun. But recent observations of the sun’s photosphere – the lowest layer of its atmosphere and the region that releases the light that we can see – have finally found them.
Magnetic fields in the sun can bundle together, forming long structures called flux tubes. These flux tubes can drive the formation of Alfvén waves. A team of researchers, led by Dr. Marco Stangalini at Italian Space Agency (ASI,Italy) with scientists from seven other research institutes and universities, including Queen Mary’s Dr. David Tsiklauri and Ph.D. student Callum Boocock, used the European Space Agency’s IBIS to carefully monitor the sun’s photosphere.
Despite previous claims, Alfvén waves had never conclusively been found on the sun before.
The researchers validated their observations with the aid of magnetohydrodynamic (MHD) simulations, which are computer simulations of the complex plasma physics operating at the sun’s surface.
Callum Boocock, a Ph.D. student at Queen Mary’s School of Physics and Astronomy, said: “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 finding provides a crucial step to understanding why the outer solar atmosphere, the corona, has a temperature a million degrees hotter than the surface. Something much be transporting energy from the photosphere to the corona, and these Alfvén waves may be the culprit.