In the shimmering halo that crowns the Sun, scientists have finally caught the twist: tiny, magnetic corkscrews rippling through superheated gas. The newly detected waves could help explain why the Sun’s outer atmosphere burns millions of degrees hotter than its surface.
The century-old solar riddle
For decades, the Sun’s corona has posed a paradox. The visible surface, or photosphere, idles around 5,500°C, yet the diffuse atmosphere above it soars beyond a million degrees. Something is ferrying energy upward and unleashing it aloft, but identifying the culprit has been one of solar physics’ longest-running pursuits.
Researchers have long suspected Alfvén waves—magnetic disturbances that travel through plasma—as stealthy couriers of that heat. First proposed in 1942 by Nobel laureate Hannes Alfvén, these waves can carry energy along the Sun’s tangled magnetic field lines like vibrations on a taut guitar string. Theoreticians pointed to a specific form, small-scale torsional Alfvén waves—twisting motions that rotate the magnetic field around its axis—as an especially efficient way to move energy into the corona. Until now, they were theorized but not directly seen.
Catching a twist in the light
That changed with the U.S. National Science Foundation’s Daniel K. Inouye Solar Telescope in Hawaii, the most powerful solar instrument ever built. With a four-meter primary mirror and a coronal spectropolarimeter known as Cryo-NIRSP, the telescope can track the subtlest motions in the corona by measuring shifts in light from ionized elements, including iron heated to roughly 1.6 million degrees Celsius.
Led by Professor Richard Morton of Northumbria University, a team used those capabilities to isolate the telltale, back-and-forth twist of torsional Alfvén waves. The trick was to separate them from the corona’s more familiar “swaying” motions—so-called kink waves that rock entire magnetic structures. Spectroscopy provided the key: torsional waves reveal themselves as simultaneous red and blue shifts on opposite sides of a magnetic strand, a signature of twisting rather than swaying.
“The movement of plasma in the sun’s corona is dominated by swaying motions,” Morton said. “These mask the torsional motions, so I had to develop a way of removing the swaying to find the twisting.”
Morton calls the result “the first direct evidence” of these elusive small-scale waves in the corona—signals researchers have chased since the 1940s. The observations, published in Nature Astronomy, relied on new analytical techniques honed specifically for the Inouye telescope’s data. Those methods, paired with the instrument’s unprecedented sensitivity, finally brought the twisting to light.
Why tiny waves pack enormous power
Alfvén waves have been seen before, but typically as larger, isolated events linked to solar flares. The newly observed torsional waves appear to be ever-present, a background hum woven into the corona’s daily life. Because they tend to avoid dissipating too quickly, they can carry energy across large distances before converting it into heat.
In the emerging picture, the Sun’s surface motions jostle magnetic field lines, launching countless small twists that propagate upward. As they interact and cascade to smaller scales, they feed turbulence—a process long predicted to heat plasma and potentially drive the solar wind. That wind, a continuous outflow of charged particles, pervades the solar system and sculpts space weather throughout Earth’s neighborhood.
The discovery strengthens those theories. “This research provides essential validation for the range of theoretical models that describe how Alfvén wave turbulence powers the solar atmosphere,” Morton said. “Having direct observations finally allows us to test these models against reality.” It may also clarify the origin of “magnetic switchbacks,” sudden reversals in the solar wind’s magnetic field, observed by NASA’s Parker Solar Probe and thought to carry significant energy.
A global effort, and a new era of data
The Inouye Solar Telescope represents two decades of international planning and development, culminating in an observatory capable of mapping the Sun’s magnetic environment with exquisite resolution. Cryo-NIRSP, its cutting-edge coronal spectrometer, is tuned to the faintest whispers of the outer atmosphere and is highly sensitive to plasma motion. That sensitivity made it possible to separate twisting from swaying in a forest of competing signals.
Morton and colleagues—from institutions including Peking University, KU Leuven, Queen Mary University of London, the Chinese Academy of Sciences, and the NSF’s National Solar Observatory—used the instrument while the telescope was still in commissioning. Their analysis focused on iron emission lines that reveal both the direction and speed of plasma flows. By filtering out the dominant kink motions and highlighting opposite-sided red-blue patterns, they traced torsional Alfvén waves climbing along magnetic structures in real time.
The study, Evidence for small-scale torsional Alfvén waves in the solar corona, appears in Nature Astronomy (DOI: 10.1038/s41550-025-02690-9). It builds on a string of recent papers by Morton and collaborators that tracked high-frequency Alfvénic waves and probed their origins, steadily tightening the connection between wave energy and coronal heat. With direct evidence now in hand, the next step is to measure how these twists evolve and dissipate.
From the Sun to our power grids
Understanding how the corona stays hot is more than a physics triumph; it is a practical need in a technology-dependent world. Energy borne by waves in the solar atmosphere shapes the solar wind, which in turn carries magnetic disturbances that can buffet Earth’s space environment. Strong bursts can disrupt satellites, degrade GPS accuracy, interfere with radio communications, and even induce currents that threaten power grids.
By pinpointing a persistent, energy-rich wave process, the new observations offer a pathway to better models of space weather. They also set the stage for coordinated studies that connect the Sun’s surface motions to the wind sampled in situ by spacecraft. As the Inouye telescope continues to open its aperture to the corona, researchers will be able to watch the generation, propagation, and eventual dissipation of torsional waves across a range of solar conditions.
That link—between what telescopes see at the Sun and what spacecraft feel in the solar wind—could help forecasters anticipate hazardous conditions days in advance. It may also reveal how the Sun’s activity cycle modulates the supply of wave energy, offering clues to why some years are stormier than others.
- Key insight: small-scale, ever-present torsional Alfvén waves now have direct observational proof in the corona.
- Why it matters: these twists can transport and deposit energy efficiently, offering a viable mechanism for coronal heating and influencing the solar wind.
- What’s next: track how the waves evolve and dissipate, refine turbulence models, and tie remote sensing to in situ measurements for improved space-weather prediction.