Astronomers first observed “nanoflares” on the Sun

(ORDO NEWS) — The higher from Earth, the colder the atmosphere becomes. However, on the Sun, everything happens the other way around: the deep layers of its atmosphere are heated “only” to 5000-6000 ° C, while the temperature of the outer corona reaches millions of degrees. This paradox remains unresolved to this day, although back in the 1970s the famous heliophysicist Eugene Parker suggested that “nanoflares” bring additional heat to the corona.

Such explosive bursts of energy should be much more numerous than ordinary solar flares, but also billions of times weaker. Therefore, it has not yet been possible to detect them in an extremely stormy light. Only in recent years some indirect evidence of their existence began to appear. So, in the corona of the star, areas were found that were heated exactly as predicted by the theory of nanoflares, and high-energy photons were caught near the Earth, which could be ejected by just such a process.

Only in our time have astronomers’ instruments become sensitive enough to see nanoflares. And the first direct images were recently obtained thanks to the spectrograph of the American IRIS probe. Shah Bahauddin and his colleagues report this in an article published in the journal Nature Astronomy.

“From theory, we know what to look for,” the scientist said in an interview with the NASA press service, “we know what kind of imprint a nanoflash should leave.” He named two key features of this process. First, like an ordinary flash, it should arise in the process of an explosive reconnection of the magnetic field lines, which is reflected by an extremely sharp and powerful heating of the plasma, uncharacteristic for other processes. Second, this heating must reach the corona and not remain in the lower layers of the solar atmosphere.

Scientists drew attention to small (about hundreds of kilometers), but extremely bright loops, which the device registered directly at the border of the solar corona. Their temperature was indeed extremely high, reaching millions of degrees. Moreover, the plasma of these loops was heated in a very strange way. The sun is made up of hydrogen and helium, with few other elements. In this case, in bright loops, relatively light elements (such as oxygen) were heated more weakly than heavier ones (for example, silicon).

“If you push a light ball, it will roll on the floor faster than a heavy one,” explains Bahauddin. – But in this case, heavier elements are thrown out at a speed of about 60 miles per second (350 thousand kilometers per hour. – Editor’s note), and lighter ones – almost at zero. It’s totally counterintuitive.” However, this paradox has become an important piece of evidence that scientists have clung to.

They modeled various processes that can cause heating of solar plasma, showing that only switching the magnetic field lines is able to transfer more energy to heavy nuclei than to light ones. With such a switch, an electric current arises for a short time, entraining the plasma ions in motion. The longer the ion continues to move in this direction, the more it accelerates; therefore, the heavier ions with their high inertia have time to receive more energy. The lungs “go astray” earlier and accelerate less.

Thus, both signs of nanoflares mentioned by Bahauddin were identified. Moreover, modeling predicted that they should only occur in plasma with certain proportions of oxygen and silicon. Scientists have checked the observational data – and indeed found that bright loops are characterized by the desired content of these elements.

Finally, the conclusions were confirmed by the SDO space observatory, which monitors the solar corona. They showed that the appearance of bright loops shallow under it after a short period of time leads to the heating of the corresponding section of the crown. In total, it turned out to trace 10 such events. “With just a 20 second delay,” adds Bahauddin. “We saw an increase in brightness, and then we saw the corona suddenly become overheated to many millions of degrees.”


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