Researchers have captured the first direct evidence of small-scale torsional Alfvén waves in the Sun's corona, potentially explaining its extreme heat. Using the Daniel K. Inouye Solar Telescope in Hawaii, the team observed these magnetic waves twisting through the solar atmosphere. The discovery, published on October 24 in Nature Astronomy, validates theories dating back to the 1940s.
The Sun's corona, its outer atmosphere, reaches millions of degrees Celsius—far hotter than the surface at around 5,500°C—yet the mechanism behind this has puzzled scientists for decades. Now, a breakthrough study led by Professor Richard Morton of Northumbria University has identified torsional Alfvén waves as a likely contributor to this heating.
Alfvén waves, magnetic vibrations in plasma first predicted in 1942 by Nobel laureate Hannes Alfvén, have been theorized to transfer energy from the Sun's interior to its corona. While larger versions of these waves have been observed in association with solar flares, the smaller, twisting torsional type had evaded direct detection until now. Morton's team used the U.S. National Science Foundation's Daniel K. Inouye Solar Telescope on Maui, Hawaii, equipped with the advanced Cryogenic Near Infrared Spectropolarimeter (Cryo-NIRSP). This instrument allowed them to track superheated iron atoms in the corona, reaching 1.6 million degrees Celsius, and detect subtle twisting motions masked by more prominent swaying.
"This discovery ends a protracted search for these waves that has its origins in the 1940s," Morton said. "We've finally been able to directly observe these torsional motions twisting the magnetic field lines back and forth in the corona." The telescope's four-meter mirror, the largest for solar observations, enabled unprecedented resolution of these fine structures.
The research, a collaboration involving institutions from the UK, China, Belgium, and the U.S., including Peking University, KU Leuven, Queen Mary University of London, the Chinese Academy of Sciences, and the NSF National Solar Observatory, was published in Nature Astronomy (DOI: 10.1038/s41550-025-02690-9). It builds on Morton's earlier 2025 papers in The Astrophysical Journal and its Letters.
Beyond solving a solar mystery, the findings could improve space weather predictions. These waves may drive the solar wind, which affects satellites, GPS, and power grids on Earth, and explain magnetic switchbacks detected by NASA's Parker Solar Probe. "This research provides essential validation for the range of theoretical models that describe how Alfvén wave turbulence powers the solar atmosphere," Morton added. Future observations with the Inouye telescope promise deeper insights into solar energy dynamics.