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| (DrPixel/Moment/Getty Images) |
Scientists have been trying to figure out how the Sun's corona, or outer atmosphere, becomes so scorching hot while its surface remains comparatively cool for decades. A recent study has provided a significant clue.
The first convincing evidence of small-scale torsional Alfvén waves across the corona has been reported by an international team of scientists. These waves travel through magnetic fields, twisting along the way and carrying plasma upward.
Up until recently, scientists have only seen isolated, larger Alfvén waves that coincided with solar flares. Although not directly detected, the existence of smaller Alfvén waves in the corona had been proposed.
These waves aid in the explanation of how extremely hot
plasma moves from the Sun's surface, where temperatures are about 5,500 °C
(10,000 °F), to the corona, where temperatures reach millions of degrees
Celsius before releasing its energy.
"This discovery ends a protracted search for these waves that has its
origins in the 1940s," Northumbria University physicist Richard Morton
explains.
"We've finally been able to directly observe these torsional motions
twisting the magnetic field lines back and forth in the corona."
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| Illustration showing small-scale torsional Alfvén waves twisting magnetic field lines in the Sun's corona. (NSF/NSO/AURA/J. Williams) |
The US National Science Foundation Daniel K. Inouye Solar Telescope in Hawaii, the most potent solar telescope in the world, provided high-resolution imagery that enabled the finding.
The telescope's instruments allow it to precisely
detect the motion of solar plasma, or charged particles. The movement of
superheated iron, which emits bluer light signatures as it approaches Earth and
redder light signatures as it goes away, was used to follow the plasma.
The data showed the movement of plasma and the twisting motion that the
researchers were searching for once they were able to eliminate the
interference of other plasma wave motions swaying back and forth.
"The movement of plasma in the Sun's corona is dominated by swaying
motions," Morton states. "These mask the torsional motions, so I had
to develop a way of removing the swaying to find the twisting."
These discoveries improve our understanding of how the
Sun's enormous furnace functions and contribute to our understanding of the
solar winds that emerge from the Sun and travel all the way to Earth, possibly
disrupting power systems and satellite networks.
It's possible that small-scale torsional Alfvén waves are enabling the corona
attain its absurdly high temperatures and providing the forces required to
drive these winds past the Sun's gravitational pull.
Space weather forecasts can be enhanced by seeing the processes in motion and
precisely modeling them, which may provide us with better warning of
geomagnetic storms that could affect Earth.
Future research can examine the processes and dispersion of these tiny Alfvén waves in greater detail and over larger coronal regions now that we have identified them. More thorough testing and research can be done on other theories regarding how the Sun functions.
"This research provides essential validation for the range of theoretical models that describe how Alfvén wave turbulence powers the solar atmosphere," Morton states.
"Having
direct observations finally allows us to test these models against
reality."
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