MAUI, HI – August 25, 2025 — Astronomers using the U.S. National Science Foundation’s (NSF) Daniel K. Inouye Solar Telescope have captured the highest-resolution images of a solar flare ever recorded at the H-alpha wavelength (656.28 nm). The observations, taken during the decay phase of an X1.3-class flare on August 8, 2024, reveal razor-thin coronal loops averaging just 48.2 km in width—and possibly as narrow as 21 km. These are the smallest coronal loops ever imaged, offering a breakthrough in understanding the Sun’s magnetic structures and advancing flare modeling.

Coronal Loops: Windows into the Sun’s Magnetic Field

Coronal loops are plasma arches that trace the Sun’s magnetic field lines. They often signal the build-up to solar flares—violent releases of magnetic energy that drive solar storms capable of disrupting satellites, power grids, and communications on Earth.

The Inouye team studied these loops in the H-alpha wavelength, which provides unique detail on solar structures. “This is the first time the Inouye Solar Telescope has ever observed an X-class flare,” said Cole Tamburri, lead author of the study and Ph.D. student at the University of Colorado Boulder (CU). “These flares are among the most energetic events our star produces, and we were fortunate to catch this one under perfect observing conditions.”

Unprecedented Resolution at Solar Scales

The loops imaged were astonishingly fine—averaging 48 km across, with some at the telescope’s resolution limit of ~24 km. For comparison, this is more than two and a half times sharper than any previous solar telescope could achieve.

“Before Inouye, we could only imagine what this scale looked like,” Tamburri explained. “Now we can see it directly. These are the smallest coronal loops ever imaged on the Sun.”

Maria Kazachenko, co-author and NSO scientist, added: “Knowing a telescope can theoretically do something is one thing. Actually watching it perform at that limit is exhilarating.”

From Chromosphere to Coronal Breakthroughs

The observations were made using the Inouye’s Visible Broadband Imager (VBI), initially intended for chromospheric studies. Instead, it revealed intricate coronal loop structures that directly inform flare models.

“We went in looking for one thing and stumbled across something even more intriguing,” said Kazachenko.

The discovery supports long-standing theories that coronal loops range from 10 to 100 km in width—a range that, until now, could not be confirmed. “We’re finally peering into the spatial scales we’ve been speculating about for years,” Tamburri noted. “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.”

Fundamental Building Blocks of Solar Flares

The findings suggest that these loops may represent elementary magnetic structures—the basic building blocks of flare architecture.

“If that’s the case, we’re not just resolving bundles of loops; we’re resolving individual loops for the first time,” Tamburri said. “It’s like going from seeing a forest to suddenly seeing every single tree.”

The images show dark, threadlike loops arcing above brilliant flare ribbons, with features so sharply defined that even non-specialists would recognize the complexity. Tamburri reflected: “It’s a landmark moment in solar science. We’re finally seeing the Sun at the scales it works on.”

About the NSF National Solar Observatory

The NSF National Solar Observatory (NSO) advances knowledge of the Sun as both an astronomical body and Earth’s dominant external influence. NSO operates the world’s most advanced network of ground-based solar telescopes, including the NSF Global Oscillation Network Group (GONG) and the NSF Daniel K. Inouye Solar Telescope, the world’s largest solar observatory.

These facilities enable breakthroughs in heliophysics, space weather forecasting, and stellar astrophysics by probing every layer of the Sun, from its interior to the outer corona. NSO also develops cutting-edge instrumentation, fosters research collaborations, and engages in education and public outreach. NSO is managed by the Association of Universities for Research in Astronomy, Inc. (AURA) under a cooperative agreement with NSF. More information is available at nso.edu.

Key Highlights

• Record-breaking resolution: Coronal loops as narrow as 21 km imaged for the first time.
• First X-class flare observed by the NSF Inouye Solar Telescope.
• Revealed fundamental solar structures that could be the building blocks of flare activity.
• Discovery enables improved flare modeling and potential advancements in space weather forecasting.
• Study published in The Astrophysical Journal Letters.

Original Publication
Authors: Cole A. Tamburri, Maria D. Kazachenko, Gianna Cauzzi, Adam F. Kowalski, Ryan French, Rahul Yadav, Caroline L. Evans, Yuta Notsu, Marcel F. Corchado-Albelo, Kevin P. Reardon and Alexandra Tritschler.
Journal: The Astrophysical Journal Letters
DOI: 10.3847/2041-8213/adf95e
Article Title: Unveiling Unprecedented Fine Structure in Coronal Flare Loops with the DKIST
Article Publication Date: 25-Aug-2025

Original Source: https://iopscience.iop.org/article/10.3847/2041-8213/adf95e