Why is the atmosphere of the sun hotter than its surface?
Life experience tells us that the closer you put your hand to a flame, the hotter your hand will be. However, in space, many things do not work as everyday experience suggests: for example, the temperature of the visible surface of the Sun is “only” 5800 K (5526.85 ° C), but at a distance, in the outer layers of the star’s atmosphere, it rises to millions of degrees.
Try to solve this small private problem, known as the Problems of heating the solar corona, one of the unresolved problems of modern physics! When the phenomenon was discovered, it seemed to scientists that the solar corona violates the second law of thermodynamics - after all, energy from the inside of a star cannot be transferred to the corona region, bypassing the surface.
Until 2007, there were two main theories explaining the heating of the solar corona. One said that magnetic fields accelerate the corona plasma to incredible energies, so that it acquires a temperature above the surface temperature. The authors of the second theory were inclined to believe that energy breaks into the atmosphere from inside the star.
The research of Bart De Pontieu and his colleagues proved that the shock waves emanating from the bowels of the star have enough energy to constantly energize the corona.
In 2013, NASA launched the IRIS probe, which continuously records the boundary between the surface of the Sun and the corona in different ranges. His goal was to answer the same question: does the solar corona have one constant source of heat, or does energy enter the atmosphere of the sun as a result of many explosions? The difference between these two explanations is very large, but it is very difficult to understand which one is true due to the huge thermal conductivity of the corona. As soon as energy is released at a single point on the Sun, the temperature rises almost instantly in the vast territory around this point - and it seems that the temperature of the corona is more or less constant.
But the IRIS apparatus recorded changes in the temperature of the corona with such a small interval that scientists were able to see many "nanoflares" (nanoflares) where magnetic lines intersected or overlapped. The question of whether there is a source of thermal radiation that uniformly and constantly heats the corona remains open, but it is now clear that at least part of the energy enters the atmosphere of the Sun from the interior of the star as a result of such explosions.
Later observations by IRIS were confirmed by the EUNIS apparatus. Now scientists are almost sure that the solar corona is heating up precisely because of many small explosions, releasing hot plasma into the atmosphere of the star, whose temperature is much higher than the temperature of the surface of the Sun.