The unusual plasma tornadoes discovered on the surface of the Sun five years ago turned out to be unlike Earth's vortices, their first three-dimensional photographs showed that they were standing still, not rotating. This was stated by scientists during a speech at the European Week of Astronomy and Science in British Liverpool.
“We found out that the appearance of these tornadoes is deceiving. In fact, the magnetic field in them is not elongated vertically, as we assumed, but horizontally, and the plasma moves mainly in the same direction. These structures have turned into 'tornadoes' in SDO images due to distortion associated with the angle from which we look at them,”said Nicholas Labross from the University of Glasgow, Scotland.
The high temperature of the corona, the uppermost layer of the solar atmosphere, is still a mystery to astrophysicists. The underlying layers of the Sun - the chromosphere and photosphere - are heated to a temperature of ten thousand degrees Kelvin. In the boundary layer between the corona and the photosphere several kilometers thick, this temperature increases hundreds of thousands of times and reaches millions of degrees Kelvin.
A complete explanation of this phenomenon, which is not in doubt among most scientists, does not yet exist. Many astronomers believe that the Sun's atmosphere is heated by powerful plasma ejections and flares that periodically occur on its surface at those points where prominences and their younger "sisters" - spicules appear, but unequivocal evidence of this has not been found.
The first hints of a corona heating mechanism, Labrosse says, were found, as scientists then believed, in March 2012 by SDO probe cameras that have been studying the corona of the sun since February 2010.
By examining the foundations of the vicinity of the prominences, British astronomers were able to find several giant magnetic structures similar in shape to a tornado. These fiery whirlwinds, in which matter moved at a speed of 300 thousand kilometers per hour, did not stand still, but "walked" along the surface of the luminary, lifting matter from its depths into the coronosphere along a spiral trajectory.
This movement, reminiscent of how the air moves inside terrestrial hurricanes, scientists later considered one of the main mechanisms of heating and acceleration of matter in the sun's corona, with which, however, many other astrophysicists did not agree. Labrosse and his colleagues found the first evidence that this is really not the case by creating the first 3D map of these plasma tornadoes.
To do this, scientists took advantage of the fact that any rapidly moving matter emitting light will look slightly different when moving in our direction and away from us. In accordance with this principle, which physicists call the "Doppler effect", in the first case it will seem to us more "blue", and in the second - more "red".
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SDO cameras cannot be used to measure the solar spectrum with high accuracy, and so Labross and his team had to combine images from the NASA probe with data that were obtained at the same time using the Japanese Hinode orbiting telescope, which has ultrasensitive spectrometers.
By measuring the strength of the Doppler effect in different parts of the solar "tornado", scientists unexpectedly discovered that they did not look at all the way they imagined them from the SDO images. It turned out that the incandescent plasma moves in them not upward in a spiral, but in a circle, in fact, remaining at the same height relative to the surface of the star.
This manner of plasma movement, as astrophysicists explain, suggests that these structures are similar in their real form not to tornadoes, but to thick threads or "hair", which are no different in structure from ordinary prominences. In other words, there are no tornadoes on the Sun, and they cannot participate in the heating of the corona, which brings scientists back to this mystery, Labrosse concludes.
