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EI2GYB > ASTRO 29.10.25 23:08z 51 Lines 6491 Bytes #128 (0) @ WW
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Subj: The Sun's Atmosphere Pulses With Hidden Twisting Waves
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The Sun's Atmosphere Pulses With Hidden Twisting Waves
October 24, 2025
By NSO
SCIENTISTS SPOT LONG-HYPOTHESIZED TWISTING MAGNETIC WAVES IN THE SUN'S CORONA WITH NSF INOUYE SOLAR TELESCOPE, HINTING AT A HIDDEN ENGINE DRIVING KEY SOLAR PHENOMENA
For more than half a century, scientists have been puzzled by one of the Sun's unsolved mysteries: why is its outer atmosphere, the corona, millions of degrees hotter than the solar surface below? This superheated crown not only glows brilliantly during total solar eclipses but also spews out the solar wind-a fluctuating stream of charged particles that bathes Earth and the rest of the solar system. The source of the corona's extreme heat and the driving force behind this wind remain among astrophysics' most persistent unanswered questions. The U.S. National Science Foundation (NSF) Daniel K. Inouye Solar Telescope was built to shed light on this and other outstanding questions.
Researchers know that the churning, boiling motions inside the Sun contain enormous amounts of energy. Yet exactly how that energy travels upward and dissipates into the corona is a puzzle, and the topic of a new study using Inouye data. "It remains a mystery how the Sun's atmosphere is heated to millions of degrees and blows out a fluctuating stream of plasma," says solar physicist Thomas Schad of the NSF National Solar Observatory (NSO), and a co-author of this study. "It's likely that the outer portion of the Sun's interior provides the mechanical energy for this heat and wind, but it remains difficult to pin down how that energy gets transported upward, and how it can dump its energy into the Sun's tenuous corona."
One promising candidate for carrying this energy into the corona is waves. Just as earthquakes ripple through Earth's crust with different kinds of vibrations-some fast and jolting, others slow yet destructive-the Sun's magnetic field can host a rich spectrum of wave motions. Among them are so-called magnetic plasma waves, which can twist and pulse in different ways along the Sun's tangled magnetic field lines.
In the study, led by Richard Morton of Northumbria University, and published in Nature Astronomy, scientists report the first observational evidence of one elusive variety: torsional Alfv‚n waves. These waves are akin to back and forth twisting motions of a stretched rubber band, spiraling energy along magnetic field lines. For decades, they were predicted but never conclusively observed in the Sun's corona. Initial measurements suggest they may carry as much energy as another well-studied class of waves, known as kink waves. If confirmed, torsional Alfv‚n waves could play a starring role in explaining how the corona is heated, and why the solar wind blows.
The breakthrough has been possible thanks to the Inouye Solar Telescope, built and operated by NSO near the summit of Maui's Haleakal?, in Hawai'i. The Inouye boasts the most advanced coronal instrument of its kind: the Cryogenic Near-Infrared Spectropolarimeter, or CryoNIRSP. This cutting-edge spectrometer can measure the corona's delicate light signatures with unprecedented clarity. Morton's team used it to track the Doppler shifts-tiny wavelength changes caused by motion-of a highly ionized iron line (Fe XIII) emitted at a scorching 1.6 million degrees Celsius. With a spatial resolution of about 500 kilometers and sensitivity to motions slower than 0.1 kilometers per second, CryoNIRSP was able to reveal the twisting dance of plasma that marks these long-sought waves.
The discovery is a milestone in a decades-long hunt. Astronomers have known since the early 2000s that magnetic waves are widespread in the solar atmosphere, but only now can they probe the smallest scales where key physical processes unfold. Torsional Alfv‚n waves, in particular, were expected to form in the finely structured loops of plasma that lace the corona, but remained hidden until the Inouyes's new window on the Sun opened.
Schad likens the situation to seismology. "Just as the S-waves turned out to be the most important to understand an earthquake's destructive power, the identification and continued study of these discovered waves may unlock an understanding of why the Sun's corona is hot and how the solar wind is created and accelerated," he says.
The heating of the Sun's corona powers the solar wind resulting in the phenomenon known as space weather-the dynamic conditions of space, originating from the Sun, that are able to disrupt satellites, power grids, and astronauts' safety. Unlocking the mystery of coronal heating is thus not only a triumph for fundamental physics but also essential for protecting our technological society. With the advent of the Inouye Solar Telescope and new discoveries like torsional Alfv‚n waves, scientists are closer than ever to unraveling how our star sustains its mysterious crown.
A press release out of Northumbria University is now available. The paper describing this study, titled "Evidence for small-scale torsional Alfv‚n waves in the solar corona" is available in Nature Astronomy.
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