For 83 years, solar physicists have been hunting ghosts. They knew torsional Alfven waves had to exist somewhere in the Sun’s blazing atmosphere, twisting through magnetic field lines like invisible corkscrews. They just could not see them. Until now.
A team led by Professor Richard Morton at Northumbria University has finally captured direct evidence of these elusive waves in the Sun’s corona, using the world’s most powerful solar telescope perched on a Hawaiian mountaintop. The discovery, published today in Nature Astronomy, might finally crack one of the Sun’s most perplexing riddles: why its outer atmosphere burns at millions of degrees while the surface below stays a comparatively cool 5,500 degrees Celsius.
The answer, it turns out, may lie in waves we could not see.
The Difference Between Swaying and Twisting
Alfven waves are magnetic disturbances that ripple through plasma, the fourth state of matter that makes up the Sun. Scientists have spotted the larger, isolated cousins of these waves before, usually linked to dramatic solar flares. But the small, persistent torsional type that could be steadily pumping energy into the corona? Those remained theoretical, predicted in 1942 by Nobel laureate Hannes Alfven but never directly observed.
The problem was not just seeing them. It was separating them from all the other motion happening in the corona. Morton describes the challenge in simple terms: the plasma’s movement is dominated by swaying motions that completely mask the twisting. To find the twist, he had to develop entirely new analytical techniques to strip away the sway.
What made the breakthrough possible was the Daniel K. Inouye Solar Telescope’s Cryogenic Near Infrared Spectropolarimeter, a instrument so sensitive it can track iron heated to 1.6 million degrees Celsius and detect the tiniest shifts in how plasma moves. With a mirror four meters wide, four times larger than previous solar telescopes, the facility represents two decades of international planning.
“This discovery ends a protracted search for these waves that has its origins in the 1940s. We have finally been able to directly observe these torsional motions twisting the magnetic field lines back and forth in the corona.”
The waves reveal themselves through spectroscopic analysis, creating characteristic red and blue shifts on opposite sides of magnetic structures as plasma moves toward and away from Earth. Unlike the familiar kink waves that cause entire magnetic structures to sway visibly in solar films, torsional Alfven waves operate at a scale that requires this kind of precision measurement.
Why This Matters Beyond the Sun
The corona, visible as a ghostly halo during solar eclipses, reaches temperatures exceeding one million degrees Celsius. That heat accelerates plasma away from the Sun as the solar wind, which fills our entire solar system and carries magnetic disturbances that can wreak havoc on Earth. Satellite communications fail. GPS systems glitch. Power grids overload.
Understanding how energy moves through the corona has practical stakes. Alfven waves may also generate magnetic switchbacks, significant energy carriers in the solar wind that NASA’s Parker Solar Probe has observed up close.
“This research provides essential validation for the range of theoretical models that describe how Alfven wave turbulence powers the solar atmosphere. Having direct observations finally allows us to test these models against reality.”
Morton won observation time on the telescope while it was still being tested, a calculated gamble that paid off. Northumbria University has been involved in the telescope’s development for years, as part of a UK consortium that designed cameras for the Visible Broadband Imager.
The discovery represents a major international effort, with collaborators from Peking University, KU Leuven, Queen Mary University of London, the Chinese Academy of Sciences, and the NSF National Solar Observatory. It is also Morton’s third paper this year on Alfven waves, following publications in The Astrophysical Journal in April and June.
The team expects their work will spark new investigations into how these waves propagate and release energy in the corona. After 83 years of searching, the hunt is over. Now the real work of understanding what these waves do can begin.