For decades, scientists have wondered how the Sun\u2019s outer atmosphere \u2014 the corona \u2014 burns millions of degrees hotter than its surface. A new study led by Northumbria University physicist Richard Morton offers a major clue: the Sun\u2019s heat may come from tiny magnetic waves that twist and ripple through its outer layers like an invisible dance.<\/p>\n
Cracking the Corona\u2019s Heat Mystery<\/p>\n
The Sun\u2019s visible surface, called the photosphere, sits at about 5,500 degrees Celsius. Yet the corona above it reaches temperatures exceeding a million degrees. For that to happen, something must transport and amplify energy upward \u2014 and fast. The heated plasma escaping from the corona forms the solar wind, a constant stream of charged particles that shapes space weather and interacts with planetary magnetic fields, including Earth\u2019s.<\/p>\n
Scientists have long suspected that waves moving along the Sun\u2019s magnetic field lines \u2014 known as Alfv\u00e9n waves, after Nobel laureate Hannes Alfv\u00e9n \u2014 might carry that energy. But while large, violent versions of these waves had been observed during solar flares, the small, constant ones believed to power the Sun itself remained elusive. Until now.<\/p>\n
An artist’s representation of twisting magnetic waves (inset) revealed for the first time by the NSF Inouye Solar Telescope. These upward-traveling torsional waves coexist with other wave types and may be an essential ingredient in solving the mystery of why the sun’s atmosphere is so hot. (2025). (CREDIT: NSF\/NSO\/AURA\/J. Williams) A Powerful New Look at the Sun<\/p>\n
Morton and his international team captured the first direct evidence of these small-scale \u201ctorsional Alfv\u00e9n waves,\u201d using the world\u2019s most advanced solar telescope \u2014 the Daniel K. Inouye Solar Telescope (DKIST) in Hawaii. Equipped with its Cryogenic Near Infrared Spectropolarimeter (Cryo-NIRSP), DKIST can detect fine details in the corona that were previously impossible to see.<\/p>\n
With a four-meter mirror \u2014 the largest ever built for solar observation \u2014 and a specialized infrared spectrometer<\/a>, the telescope observed iron in the corona heated to about 1.6 million degrees Celsius. The data, collected on October 30, 2023, revealed subtle shifts in light that showed plasma twisting back and forth along magnetic flux tubes about 0.1 solar radii above the Sun\u2019s visible edge.<\/p>\n Morton explained that the challenge wasn\u2019t just spotting motion, but separating one type of wave from another. \u201cThe movement of plasma in the sun\u2019s corona is dominated by swaying motions,\u201d he said. \u201cThese mask the torsional motions, so I had to develop a way of removing the swaying to find the twisting.\u201d<\/p>\n Watching the Sun\u2019s Magnetic Dance<\/p>\n By filtering and analyzing the Doppler shifts<\/a> \u2014 changes in wavelength caused by plasma moving toward or away from Earth \u2014 the researchers found the telltale red and blue pattern of twisting motion: one side of a magnetic tube moving toward us while the other moves away. This is the fingerprint of torsional Alfv\u00e9n waves.<\/p>\n Image of the solar corona taken with the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory in the extreme ultraviolet (193\u2009\u00c5 channel) to provide context for the Cryo-NIRSP data. (CREDIT: Nature Astronomy) <\/p>\n The team measured twisting speeds averaging around 19.5 kilometers per second after correcting for viewing angle and other effects. That\u2019s about the speed of a high-altitude jet aircraft and strong enough to move significant amounts of energy through the solar atmosphere. These waves were found in quiet regions of the corona, not just in stormy flare zones, suggesting they occur constantly across the Sun.<\/p>\n Simulations run by the researchers supported the observations, showing that torsional motions dominate near the edges of magnetic structures while \u201ckink\u201d waves \u2014 the side-to-side swaying \u2014 dominate their centers. Together, these motions generate a steady flux of magnetic energy<\/a>.<\/p>\n Enough Energy to Power the Sun\u2019s Outer Layers<\/p>\n The study estimated that the energy carried by these Alfv\u00e9n waves ranges from about 100 to 400 watts per square meter. That\u2019s more than enough to heat the quiet corona and help accelerate the fast solar wind that streams through the solar system.<\/p>\n The data also hint that these estimates may be conservative. Because multiple magnetic tubes overlap along the line of sight and telescope resolution has limits, some of the wave energy may go undetected. Correcting for these effects could push the energy levels even higher.<\/p>\n Cryo-NIRSP (right), the Inouye’s advanced coronal spectropolarimeter, used to track twisting plasma motions in the sun’s corona. (CREDIT: NSF\/NSO\/AURA) <\/p>\n Morton\u2019s findings align with long-standing theories that Alfv\u00e9n waves convert magnetic energy into heat through turbulent interactions in the plasma. \u201cThis discovery ends a protracted search for these waves that has its origins in the 1940s,\u201d he said. \u201cWe\u2019ve finally been able to directly observe these torsional motions twisting the magnetic field lines back and forth in the corona.\u201d<\/p>\n The Global Effort Behind a Breakthrough<\/p>\n The research, published in Nature Astronomy, was a collaboration among scientists from Northumbria University<\/a>, the National Solar Observatory in Hawaii and Colorado, Peking University, KU Leuven, Queen Mary University of London, and the Chinese Academy of Sciences.<\/p>\n Northumbria University\u2019s contribution extended beyond analysis \u2014 it helped design cameras for one of DKIST\u2019s major imaging instruments. Morton secured telescope time even before full operations began, taking advantage of a rare testing window to capture the groundbreaking data.<\/p>\n Illuminating Space Weather and the Solar Wind<\/p>\n Understanding how energy moves through the Sun\u2019s atmosphere isn\u2019t just about curiosity. The solar wind \u2014 the stream of charged particles flowing from the corona<\/a> \u2014 influences the entire solar system. When it intensifies, it can disrupt satellites, interfere with GPS, and even overload power grids on Earth.<\/p>\n Results of 3D MHD simulations of wave propagation along an overdense open coronal waveguide. (CREDIT: Nature Astronomy) <\/p>\n Alfv\u00e9n waves may also explain \u201cmagnetic switchbacks,\u201d sudden reversals in solar wind direction that have been recorded by NASA\u2019s Parker Solar Probe. If these twisting motions help drive such phenomena, they could become key to forecasting space weather events more accurately.<\/p>\n This work represents the first step toward decoding how energy flows and dissipates in the corona. The team plans to follow the waves farther out from the Sun to see how they evolve and where they release their energy as heat. Future studies combining DKIST\u2019s data with images from spacecraft like the Parker Solar Probe<\/a> could reveal the full life cycle of these magnetic waves.<\/p>\n As Morton puts it, having direct observations \u201cfinally allows us to test these models against reality.\u201d For the first time, solar physicists can match their equations and computer models to what\u2019s really happening on the Sun\u2019s surface.<\/p>\n Practical Implications of the Research<\/p>\n The discovery of small-scale torsional Alfv\u00e9n waves reshapes how scientists understand the Sun\u2019s energy system. It provides a credible explanation for why the corona burns millions of degrees hotter than the surface and how the solar wind is accelerated. <\/p>\n