The Swedish 1-m Solar Telescope (SST) has recently been upgraded with a new instrument called CHROMIS. It provides an unprecendented view of the atmosphere of the Sun, specifically a layer in the atmosphere called chromosphere. With CHROMIS, the SST can observe details as small as 60 km, and provides the sharpest images of the Sun ever observed.
One of the big open questions is why the chromosphere is so hot. Neither radiation from the bright solar surface below, nor sound waves excited by the motion of the hot bubbles of solar gas below the surface can provide enough energy. This is especially the case in areas where a large amount of magnetic field is erupting through the solar surface into the chromosphere, which are calles emerging active regions. One of the theories is that electric currents induced by the magnetic field of the Sun can provide the required energy in such emerging active regions.
Researchers from the Institute for Solar Physics at Stockholm University performed a study using CHROMIS investigating this theory by observing an emerging active region. The light observed with CHROMIS is a direct measure of the temperature in the chromosphere. The polarization of the light observed simultaneously with another instrument on the SST called CRISP was analysed to measure the magnetic field. The study found that there is a strong correlation between the temperature in the chromosphere and the strength of the magnetic field. It so provides a firm confirmation of the role of the magnetic field in heating the chromosphere.
Understanding exactly how the magnetic field creates the electric currents requires instruments that are even more sensitive than CHROMIS and CRISP and telescopes that can resolve even smaller details on the Sun than SST. The European Solar Telescope, planned to become operational in 2026, will do so. The study was published as a highlight in the international journal Astronomy & Astrophysics. More information about the highlight can be found here