A mind-bending mystery of our Sun has finally been solved

Scientists have finally spotted something they have been searching for since the 1940s: small-scale torsional Alfvén waves in the Sun’s corona. Torsional Alfvén waves are rotating magnetic waves that travel through plasma along magnetic field lines, twisting them back and forth like a coiled spring. First predicted in 1942 by Swedish physicist Hannes Alfvén, these waves are believed to transport large amounts of energy through the Sun’s atmosphere. They were detected using the Daniel K. Inouye Solar Telescope in Hawaii, the most powerful solar telescope in the world. The discovery, published in Nature Astronomy, could help explain why the Sun’s outer atmosphere is so much hotter than its surface.

The corona, the Sun’s outermost atmospheric layer, extends millions of kilometers into space and is made of extremely hot ionized plasma. Plasma is often described as the fourth state of matter, where atoms become so energized that electrons separate from atomic nuclei, creating electrically charged particles strongly influenced by magnetic fields. Although the Sun’s visible surface is far cooler at 5,500 degrees Celsius, the corona shockingly reaches temperatures above one million degrees Celsius, creating the long-standing “coronal heating problem.” Its plasma flows outward as the solar wind, a supersonic stream of charged particles that fills our solar system. The solar wind shapes the heliosphere and can disturb satellites, GPS systems, and electrical grids on Earth. How the corona receives enough energy to sustain such temperatures has been debated for decades.

Alfvén waves have long been considered one of the leading explanations. In a plasma made up of many flux tubes — narrow magnetic structures that channel plasma and energy through the Sun’s atmosphere — the only pure Alfvén mode is torsional, meaning it twists magnetic field lines around their central axis rather than swaying them side to side. These magnetic structures guide the movement of charged particles because plasma naturally follows magnetic field lines.

Professor Richard Morton of Northumbria University, who led the study, said: “This discovery ends a protracted search for these waves that has its origins in the 1940s. We've finally been able to directly observe these torsional motions twisting the magnetic field lines back and forth in the corona.”

The breakthrough was made possible by the telescope’s Cryogenic Near Infrared Spectropolarimeter (Cryo-NIRSP), an instrument designed to observe extremely fine magnetic and plasma structures in the corona. Morton tracked iron heated to 1.6 million degrees Celsius and developed new techniques to separate torsional motions from the more common swaying motions. “The movement of plasma in the sun's corona is dominated by swaying motions. These mask the torsional motions, so I had to develop a way of removing the swaying to find the twisting,” he explained.

Unlike kink waves, which make entire magnetic structures sway, torsional Alfvén waves produce twisting motions that can only be detected through spectroscopy, the scientific study of how matter interacts with light. In solar physics, spectroscopy measures tiny wavelength shifts caused by moving plasma through the Doppler effect. Plasma moving toward Earth produces a slight “blue shift,” while plasma moving away produces a “red shift.” By examining these opposite red and blue signatures on either side of magnetic structures, scientists can detect hidden twisting motions within the corona. The data showed that the quiet corona supports these torsional waves continuously.

Their measured amplitudes are small, but scientists believe they are underestimated because of the way the data is collected. Even so, the waves may carry a large fraction of the energy needed to power the corona and drive the solar wind.

“This research provides essential validation for the range of theoretical models that describe how Alfvén wave turbulence powers the solar atmosphere,” Morton added. “Having direct observations finally allows us to test these models against reality.”

The discovery matters not only for understanding the Sun but also for predicting space weather. The solar wind carries magnetic disturbances that can disrupt satellites, GPS systems, radio communication, and power grids on Earth. Alfvén waves may also explain “magnetic switchbacks” observed by NASA’s Parker Solar Probe, which are thought to transport significant energy through the solar wind.

The study involved researchers from China, Belgium, the UK, and the U.S., showing the scale of international collaboration in solar science. With the Inouye Solar Telescope now delivering extremely high-resolution views of the corona, scientists expect more insights into how these magnetic waves move, interact, and release energy throughout the Sun’s atmosphere.

Source: Northumbria University, Nature

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