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EUI detects high-frequency sideways waves

High-frequency sideways waves were detected for the first time using Europe's new solar observatory Solar Orbiter. These sideways waves are much more energetic than previously observed waves, and could play a role in heating the solar corona. Solar Orbiter is a space mission flying close to the Sun, allowing for a high spatial resolution and high frame rate, that could not be previously achieved. The rapid waves were discovered by a team of scientists from KU Leuven and the Solar-Terrestrial Centre of Excellence.

Video file
EUI observes high-frequency sideways waves

These rapid waves address one of the important questions in solar physics that puzzles scientists which is called the coronal heating problem. It was discovered first in the 1940s when scientists found that the temperature of the Sun suddenly changes when going away from its surface into the corona, and dramatically rises from several thousand to a million degrees. It is quite unexpected, since the further you go from the heating source, the cooler it should get. For example, near a fire, the air around it becomes cooler and cooler the further you go away. In our case, the fire is the core of the Sun. However, suddenly, the air around the fire becomes hot again. Our first instinct is to check whether there is an additional source of the heating present - maybe another fire closeby. The same idea is followed by solar physicists who are looking for an additional heat source for the heating of the solar corona. One of the suggested mechanisms is waves that are present everywhere on the Sun, but up to now they were found not to be energetic enough. These newly discovered high-frequency waves are the first to carry a steady supply of energy sufficient to heat the corona.  

One of the difficulties for solving the coronal heating problem is the imaging capabilities of the current telescopes. Previous telescopes lack spatial resolution. Since the Sun is very far, it is quite hard to get good-quality pictures of it, and the small scales are blurred. However, the new European space telescope Solar Orbiter, launched in 2020, flies as close to the Sun as it can, and thus obtains high resolution images. Older telescopes also have slow frame rates for taking images, and this is a problem for observing fast solar phenomena. For example, if you take photos of a person, who blinks every two seconds but you take images every 30 seconds for 1 minute long, you might not even catch the blinks. Then you can incorrectly conclude that the person doesn’t blink at all. Thus, we could not see high-frequency waves, even if they are potentially important for heating the corona. It is only because of the new telescope Solar Orbiter, which is much closer to the Sun and has a high frame rate, that we see these new high-frequency waves.

The corona is made of coronal loops which are essentially tubes filled with hot gas that are following the magnetic field of the Sun, as shown in the mosaic observations made by EUI. 

EUI Mosaic Observations
Mosaic of 25 individual EUI-images taken on 7 March 

These tubes experience such rapid waves, which can dissipate and turn into heating. If these rapid energetic waves are then everywhere in the corona, they could heat a large part of it. The particular kind of rapid waves the researchers have discovered are called kink oscillations. Its naming is because of its typical sideways kinking of the coronal loops, as shown in the video below. 

Coronal loop motion - TRACE

The study “High-frequency Decayless Waves with Significant Energy in Solar Orbiter/EUI Observations” by Elena Petrova, Norbert Magyar, Tom Van Doorsselaere, and David Berghmans was published in The Astrophysical Journal (doi: 10.3847/1538-4357/acb26a).