It took astronomers a little over a year to analyze the sharpest-ever images of a solar flare. But they’re finally done, and the results are illuminating—literally and figuratively.

Last year, NSF’s Daniel K. Inouye Solar Telescope captured a high-resolution image of a solar flare crossed with dark strands of coronal loops. Further analysis revealed that the solar flare was an X-class flare—the most powerful class—in a decay phase. The coronal loop strands averaged around 30 miles (48 kilometers) in width, with a minimum thickness of 13 miles (21 km), which would make them the smallest coronal loops ever seen. A detailed account of the imaging and analysis was published in The Astrophysical Journal Letters on August 25, 2025.

“These flares are among the most energetic events our star produces, and we were fortunate to catch this one under perfect observing conditions,” said Cole Tamburri, study lead author and a postdoctoral student at the University of Colorado Boulder, in a release.

The solar incentive

For astronomers, every crackle, cough, and combustive explosion from the Sun registers as a warning signal for an incoming solar storm—a burst of energy with the power to jumble up Earth’s weather and network systems. That, along with the obvious academic motivations, drives researchers to zoom in on our star’s fiery surface.

Coronal loops are thin plasma arches tracing across the Sun’s magnetic field lines. These plasma ribbons often precede solar flares, so paying attention to their motion could help Earthbound observers better understand the dynamics of solar weather.

Solving a solar mystery

The finding also represents the first observational confirmation of how wide coronal loops can grow—a metric that has long remained in the realm of theory. The unprecedentedly sharp details of Inouye’s image allowed astronomers to analyze each loop.

“It’s like going from seeing a forest to suddenly seeing every single tree,” Tamburri added. “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 researchers are also wondering if coronal loops could represent “fundamental building blocks of flare architecture,” they said. If so, that knowledge alone could revolutionize how researchers perceive data from the Sun—and therefore its effect on Earth.

“It’s a landmark moment in solar science,” Tamburri said. “We’re finally seeing the Sun at the scales it works on.”