Two articles published in “The Astrophysical Journal” describe a study of what is known as the coronal heating problem. For decades, scientists have been trying to understand why the temperature on the surface of the Sun is about 6,000 Kelvin while the corona, the region between the surface and the area of ​​the outer atmosphere, can reach temperatures of several million degrees. Now a team of researchers led by Takenori Okamoto of the Solar-Terrestrial Environment Laboratory at Nagoya University and ISAS/JAXA and Patrick Antolin of the National Astronomical Observatory of Japan, Tokyo, offers an explanation, tied to resonant absorption.

American, Japanese and Europeans researchers put together observations made with the Hinode space probe, a JAXA mission NASA collaborated with, and that of NASA’s IRIS  space probe, launched in June 2013 precisely to study these solar phenomena. The data obtained were compared with simulations created with the ATERUI supercomputer at the National Astronomical Observatory of Japan (NAOJ).

The result was that the scientists were able to find the first observation evidence of resonant absorption. It’s a physical process in which two different types of magnetic waves resonate, reinforcing one of them. In particular, Alfvén waves were observed, which can propagate along a solar prominence, a filament-shaped structure that consists of dense and cold gases that move inside the corona.

For the first time scientists were able to directly observe resonant absorption between transverse waves and torsional waves, leading to a turbulent flow that heats the prominence. It’s here that the observations of the two space probes were complemented since Hinode observed the transverse motion and IRIS observed the torsional motion. It’s a perfect example of research that gives results exactly thanks to the combination of different instruments.

This is an important result because resonant absorption is an essential part of the process hypothesized to explain how magnetic waves are transformed into heat. However, it’s not the direct cause of this heating. The simulations showed that the transformed waves motion leads to a turbulence around the filaments edges which heat up the surrounding plasma.

In essence, resonant absorption is an excellent candidate for the role of the energy transport mechanism. The observations were carried out in transition regions rather than in the corona but according to the researchers this mechanism can be common in the corona as well. Now the study will focus on these mechanisms and other research on other mysteries about the Sun will benefit from the combination of data collected by Hinode and IRIS.

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