Near the summit of Maui’s Haleakalā, the NSF Daniel K. Inouye Solar Telescope – and its set of cutting-edge solar instruments, such as the Visible Tunable Filter – is set to pave the way for a deeper understanding of our home star. (Credit: NSF, NSO, AURA)
Astronomers using the Daniel K. Inouye Solar Telescope on Maui have captured some of the most detailed images ever taken of a solar flare, revealing razor-thin magnetic loops that could transform how scientists understand and predict solar storms.
The observations, recorded Aug. 8, 2024, during the decay of an X1.3-class flare, showed dark coronal loop strands with unprecedented clarity. The loops averaged 48.2 kilometers in width. Some were as thin as 21 kilometers—about one-fifth the length of Maui and the smallest coronal loops ever imaged.
“Before Inouye, we could only imagine what this scale looked like,” said Cole Tamburri, a University of Colorado Boulder Ph.D. and lead author of the study. “Now we can see it directly. These are the smallest coronal loops ever imaged on the Sun.”
A high-resolution image of the flare from the Inouye Solar Telescope, taken Aug. 8, 2024, at 20:12 UT. The image is about four Earth-diameters on each side. (Courtesy: National Solar Observatory)
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Coronal loops are arcs of superheated plasma that trace the Sun’s magnetic field lines. When those magnetic fields twist and snap, they release massive bursts of energy in the form of solar flares and storms — events that can disrupt satellites, communications and power grids on Earth.
By tuning the telescope’s Visible Broadband Imager to the H-alpha wavelength (656.28 nm), astronomers were able to isolate light emitted by hydrogen atoms in the lower solar atmosphere. The images resolve features as small as 24 kilometers — a level of detail more than twice that of the next-best solar telescope, according to researchers.
“It’s like going from seeing a forest to suddenly seeing every single tree,” Tamburri said. The scientists also credited the level of clarity to perfect observing conditions.
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It was also the first time the Inouye Solar Telescope has ever observed an X-class flare.
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Originally, the team set out to study chromospheric spectral line dynamics using the telescope’s Visible Spectropolarimeter. But the Visible Broadband Imager delivered the unexpected treasure: ultra-fine coronal structures that could directly inform advanced flare models.
“We went in looking for one thing and stumbled across something even more intriguing,” said NSO scientist and study co-author Maria Kazachenko.
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The findings confirm long-standing theories that coronal loops could be as narrow as 10 to 100 kilometers, and researchers believe they may have imaged the Sun’s fundamental magnetic building blocks for the first time.
“We’re finally peering into the spatial scales we’ve been speculating about for years,” Tamburri said. “This opens the door to studying not just their size, but their shapes, their evolution and even the scales where magnetic reconnection—the engine behind flares—occurs.”
The research team included scientists from the National Solar Observatory, the Laboratory for Atmospheric and Space Physics and the Cooperative Institute for Research in Environmental Sciences.
Their study, “Unveiling Unprecedented Fine Structure in Coronal Flare Loops with the DKIST,” was published Monday in The Astrophysical Journal Letters.
The Daniel K. Inouye Solar Telescope — the world’s largest solar telescope — is operated on Haleakalā by the National Solar Observatory under the National Science Foundation.