The clearest image of a solar flare yet captured will provide scientists with unprecedented insight into these violent events, and may significantly improve forecasts of space weather, a major threat to Earth’s technological infrastructure.
The U.S. National Science Foundation’s Daniel K. Inouye Solar Telescope captured the solar flare at the H-alpha wavelength in high resolution, clearly displaying the coronal loop strands during the decay phase of an X1.3 class flare. The event occurred on August 8, 2024, and featured loops with an average width of 48.2 kilometers, with some sections narrowing down to as narrow as 21 kilometers across the Sun’s surface.
Coronal Loops and Solar Flares
“This is the first time the Inouye Solar Telescope has ever observed an X-class flare,” said lead author Cole Tamburri. “These flares are among the most energetic events our star produces, and we were fortunate to catch this one under perfect observing conditions.”
Before solar flares lead to enormous solar energy ejections, arches of plasma called coronal loops travel along the Sun’s magnetic field lines. As the lines twist and snap, the resulting energy powers solar storms. The new H-alpha wavelength observations reveal new details that scientists have not been able to discern in earlier imagery.
The team behind the new imagery contained scientists from the National Science Foundation, the Laboratory for Atmospheric and Space Physics, the Cooperative Institute for Research in Environmental Sciences, and the University of Colorado Boulder. Their attention was focused on the coronal loops woven above the flare ribbons, some of which were so narrow that they pressed the edge of the telescope’s resolution limits.
Inouye Solar Telescope
After 25 years of planning, designing, and construction, the Inouye Solar Telescope began observations in February 2022. Outfitted with a variety of specialized instruments, Inouye is the most powerful solar telescope in the world, situated 10,000 ft above sea level near the summit of Haleakalā on Maui, Hawai’i.
“Before Inouye, we could only imagine what this scale looked like,” Tamburri explains. “Now we can see it directly. These are the smallest coronal loops ever imaged on the Sun.”
Making the new findings possible was the Visible Broadband Imager instrument on the Inouye telescope. With a resolution able to capture objects down to about 24 kilometers wide on the Sun’s surface, the Visible Broadband Imager exceeds the next best solar telescope’s clarity by two and a half times.
“Knowing a telescope can theoretically do something is one thing,” said co-author Maria Kazachenko. “Actually watching it perform at that limit is exhilarating.”
The Twist and Turns of Research
Ironically, the team’s significant discovery was quite separate from their initial research goal, even using a different instrument than originally intended. That first goal was to use the Visible Spectropolarimeter instrument on the Inouye telescope to observe chromospheric spectral line dynamics. However, when the team analyzed the data from those observations, they were surprised to discover the coronal structures used in flare models.
“We went in looking for one thing and stumbled across something even more intriguing,” Kazachenko admits.
Theoretical models have proposed coronal loop widths ranging from 10 to 100 kilometers, but this is the first time researchers have been able to confirm their typical size in observations.
“We’re finally peering into the spatial scales we’ve been speculating about for years,” says Tamburri. “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.”
Continuing to Explore Solar Flares
While there is much left for scientists to uncover about the coronal loops, one area of particular interest is whether or not they represent the fundamental building blocks of solar flares.
“If that’s the case, we’re not just resolving bundles of loops; we’re resolving individual loops for the first time,” Tamburri adds. “It’s like going from seeing a forest to suddenly seeing every single tree.”
“It’s a landmark moment in solar science,” he concludes. “We’re finally seeing the Sun at the scales it works on.”
The paper, “Unveiling Unprecedented Fine Structure in Coronal Flare Loops with the DKIST,” appeared in The Astrophysical Journal Letters on August 25, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.