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The Sun has been hiding a maddening secret in plain sight. Its surface sits at about 5,500 degrees Celsius, yet the corona, that ghostly outer atmosphere stretching millions of kilometers into space, blazes past 1 million degrees. For decades, solar physicists have wrestled with the same question: how does the outer layer end up vastly hotter than the star below it?
Now, researchers say they have finally caught one of the key suspects in the act. Using the Daniel K. Inouye Solar Telescope in Hawaii, the most powerful solar telescope on Earth, scientists have directly detected elusive twisting magnetic motions known as torsional Alfvén waves in the Sun’s corona. The finding, published in Nature Astronomy, gives fresh weight to one of the most compelling explanations for the long-running coronal heating problem.
These waves were first predicted back in 1942 by Swedish physicist Hannes Alfvén. In simple terms, they are rotating disturbances that travel through plasma along magnetic field lines, twisting those invisible structures back and forth like a wound spring. Scientists have long suspected they could carry huge amounts of energy upward through the Sun’s atmosphere. The problem was proving they were really there.
That was not easy. The corona is made of superheated plasma, a state of matter in which atoms are so energized that electrons break free from their nuclei, leaving a sea of charged particles that respond strongly to magnetism. Inside this environment, plasma threads through narrow magnetic channels often called flux tubes. In those structures, the pure Alfvén signature is not a sideways wobble but a twist.
What the telescope finally saw
The breakthrough came through the telescope’s Cryogenic Near Infrared Spectropolarimeter, or Cryo-NIRSP, an instrument built to study the corona’s fine magnetic and plasma structure in extraordinary detail. Led by Professor Richard Morton of Northumbria University, the team tracked iron heated to roughly 1.6 million degrees Celsius and devised a way to isolate twisting motions from the far more obvious swaying motions that usually dominate the scene.
Morton said the search had been dragging on since the 1940s, and the team has now been able to directly observe magnetic field lines in the corona twisting back and forth. That matters because swaying waves and twisting waves are not the same thing. Kink waves move whole magnetic structures side to side. Torsional Alfvén waves spin them around their axis.
To spot that hidden spin, the researchers relied on spectroscopy, which measures how matter interacts with light. In solar observations, moving plasma slightly shifts wavelengths through the Doppler effect. Material moving toward Earth shows a blue shift. Material moving away shows a red shift. When those opposite signals appear on either side of the same magnetic structure, they reveal a twisting motion that would otherwise stay invisible.
And that is exactly what the data showed. Even in the quiet corona, away from the most violent solar outbursts, these torsional waves appear to be present continuously.
The measured amplitudes are relatively small, but the researchers caution that the true strength of the waves is likely being underestimated by the way observations are gathered. Even with that limitation, the waves may be carrying a substantial share of the energy needed to heat the corona and help launch the solar wind.
That has consequences far beyond solar theory. The solar wind is a supersonic stream of charged particles flowing outward from the Sun, shaping the heliosphere and influencing conditions across the solar system. When magnetic disturbances ride along with it, they can interfere with satellites, GPS, radio communications, and even power grids on Earth.
This is why the discovery lands as more than a neat piece of astrophysics. It strengthens the physical models scientists use to explain how energy moves through the solar atmosphere and how turbulence powered by Alfvén waves may feed both coronal heating and the solar wind itself. It may also help explain the mysterious magnetic switchbacks detected by NASA’s Parker Solar Probe, sudden reversals in the solar wind’s magnetic field that appear to carry significant energy.
The study brought together researchers from China, Belgium, the United Kingdom, and the United States, a reminder that solving the Sun’s deepest riddles rarely happens in isolation. With the Inouye Solar Telescope now delivering unprecedented high resolution views of the corona, scientists are expecting a new wave of answers about how magnetic energy travels, tangles, and erupts above the solar surface.
After more than 80 years of theory, suspicion, and technical frustration, one of solar physics’ most stubborn mysteries has finally started to give way. Not with a bang, but with a twist.
Source: nature
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