A groundbreaking discovery in solar physics has been made by an international team of researchers who have directly observed Alfvén torsional waves in the Sun”s corona for the first time. This finding, published in Nature Astronomy, addresses an 80-year-old mystery regarding how the Sun”s outer atmosphere reaches temperatures of millions of degrees Celsius, while its surface temperature hovers around 5,500 °C.
Alfvén waves, predicted by Nobel laureate Hannes Alfvén in 1942, are magnetic disturbances capable of transferring energy through plasma. Previously, scientists had only detected larger, isolated versions of these waves, usually associated with solar flares. The recent observations were made possible through the unparalleled capabilities of the world”s most powerful solar telescope, the Daniel K. Inouye Solar Telescope (DKIST) located in Hawaii, which allowed for the detection of smaller, persistent waves that may be driving the Sun”s energy.
Professor Richard Morton from Northumbria University, who led the study, stated, “This research concludes a prolonged search that began in the 1940s. We have finally been able to directly observe these torsional movements that twist the magnetic field lines in the corona.”
The breakthrough was achieved using the Cryogenic Near Infrared Spectropolarimeter (Cryo-NIRSP) on the DKIST, an instrument designed to capture extremely fine details and respond sensitively to plasma movements. With its four-meter mirror—four times larger than previous solar telescopes—the DKIST represents two decades of international planning and development.
Morton accessed the telescope during its testing phase, utilizing Cryo-NIRSP to track heated iron moving at 1.6 million degrees Celsius within the solar corona. The discovery hinged on developing new analytical techniques capable of distinguishing various types of plasma movement. “The plasma motion in the solar corona is dominated by swaying oscillations, which mask the torsional movements,” the researcher explained. “I had to devise a method to filter out that swaying to reveal the torsion.”
Unlike known “kink” waves, which cause entire magnetic structures to sway, Alfvén torsional waves create twisting movements detectable only through spectroscopic analysis. This involves measuring how plasma moves towards or away from Earth, resulting in characteristic red and blue shifts at the ends of magnetic structures.
This discovery has profound implications for understanding the Sun. The corona, visible during solar eclipses, reaches temperatures exceeding one million degrees Celsius, driving plasma into space as solar wind, which permeates the entire solar system. Grasping how this energy is generated and propagated is crucial for improving predictions of space weather, which can disrupt communication systems, GPS, and power grids on Earth. “This research provides critical validation for theoretical models describing how Alfvén wave turbulence fuels the solar atmosphere,” Morton added. “Having direct observations finally allows us to compare these models with reality.”
The study involved experts from multiple institutions, including Northumbria University, Peking University, KU Leuven in Belgium, Queen Mary University of London, the Chinese Academy of Sciences, and the NSF National Solar Observatory in Hawaii and Colorado. Supported by scientific programs from the UK, China, and the European Union, this research marks a new era in solar physics. The team anticipates that the DKIST will enable further exploration of how these waves transport and dissipate energy in the corona, bringing science closer to understanding the energetic heart of our nearest star.
