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Scientists have long wondered why the hot soup of charged particles in our sun’s atmosphere gets hotter as it moves away from the sun’s surface.
New research may have the answer, which may reveal the super-hot nature of the sun’s outer atmosphere or “corona” due to the interesting behavior of small-scale waves in this nebulous plasma. These waves, called “kinetic Alfvén waves” or “KAWs” by scientists, are wave-like vibrations of magnetic fields, reflected by motion in the sun’s photosphere.
The results could provide an important clue to decoding the physics-like “secret of coronal heating” and why the corona is hundreds of times hotter than the visible solar “surface” or photosphere that radiates all the light which we see from the sun.
The team behind this research, led by Syed Ayaz, a researcher at the University of Alabama in Huntsville, theorizes that KAWs propagate and spread and heat the sun’s corona. As such they act as an important, albeit small-scale, mechanism by which energy is transferred within the solar plasma.
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Ayaz said this phenomenon could explain why the visible surface of the sun is around 10,000 degrees Fahrenheit (5,500 degrees Celsius) and the corona, which represents the upper part of the sun’s atmosphere, is over 2 million degrees Fahrenheit ( 1.1 million degrees Celsius).
“For many years, Alfvén waves have been proven to be the best candidates for transporting energy from one place to another,” Ayaz said recently. statement. “Until now, no solar spacecraft mission has provided predictions for these near-sun phenomena.”
How the mystery of coronal heating overcomes physics
Most of the sun’s energy comes from its core, where nuclear fusion takes place. That means the sun should becoming hotter as one moves deeper within it. Most of the layers on our star obey this principle. However, the corona, despite being millions of miles further away from the Sun’s core than the Sun’s surface, is still much hotter than the photosphere.
Ayaz and his colleagues studied the effect of KAWs in plasma floating up to a height equal to 10 times the radius of the sun. At such distances, when the waves interact with the sun’s charged plasma, which is packed with “ions,” atoms stripped of their electrons, they “dissipate rapidly, transferring all of their energy to plasma particles in heating form,” said Ayaz.
The team’s findings suggest that energy from the waves can reach the corona and heat it, although it remains to be seen how much they contribute to the corona’s temperature.
This new research “provides important insights into the critical problem of how energy in a magnetic field is transformed to heat a plasma containing charged particles such as protons and electrons,” said Gary Zank, director of the Center for Plasma Space And Aeronomic Research at the University. of Alabama was not involved in the work.
The results of the latest study are reinforced by data from the European Space Agencies Solar Orbit and NASA Solar Dynamics Observatory (SDO). The SDO previously received that another type of high-frequency magnetic wave, such as an arc propagating through the corona, can dump large amounts of energy into the sun’s outer atmosphere over time, contributing to the warming of the million-degree-warm layer.
Similar processes that provide heat to the sun’s corona were the focus of NASA’s recent sounding rocket mission. The mission, named MaGIXS-2—the second flight of the Marshall Field X-ray Spectrometer, sent into space for a few minutes in mid-July to collect X-rays from the sun.
In particular, those rays tell how often bursts of energy are fired within our star, which could help scientists reveal more about how the corona is heated.
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Even as scientists continue to piece together the answer to how the sun’s corona gets so hot, other heating mechanisms related to the sun’s magnetic field are being ruled out. For example, scientists suspected that certain S-shaped bends in the sun’s magnetic field packed enough magnetic energy to be released into the surrounding plasma, heating it up and accelerating solar wind storms.
However, an analysis of Parker Solar Probe’s first 14 laps around the sun reported in a separate paper published Monday in The Astrophysical Journal Letters found no evidence of the sought-after feature inside the corona.
Mojtaba Akhavan-Tafti, a research scientist at the University of Michigan who led the study, noted i statement that the Parker Solar Probe’s upcoming trips into the sun, probably as early as December of this year, could reveal more insights into the decades-old mystery.
The team’s study was published last week in The Astrophysical Journal.