First-ever images of powerful X1.3-class solar flare captured by solar telescope

From 93 million miles away, the Sun just got a lot more personal. Astronomers have now seen some of its finest magnetic threads in sharper detail than ever before, and those tiny features could change how you think about solar storms that shake life on Earth.

On August 8, 2024, a powerful X1.3-class flare exploded from the Sun. These are among the most energetic events our star can produce. As the flare settled down, the U.S. National Science Foundation’s Daniel K. Inouye Solar Telescope locked on at just the right moment.

Using an instrument tuned to the H-alpha wavelength of 656.28 nanometers, the team watched the flare’s decay phase unfold. In that red slice of light, the Sun’s lower atmosphere glows and fine structures stand out. What appeared above the bright flare ribbons stunned the researchers.

They saw hundreds of dark, hair-thin arches of plasma, known as coronal loops, draped over the bright flare region like threads of ink over fire. These loops followed the Sun’s twisted magnetic field lines with a delicacy scientists had only guessed at before.

“This is the first time the Inouye Solar Telescope has ever observed an X-class flare,” said lead author Cole Tamburri, a Ph.D. student at the University of Colorado Boulder supported by the Inouye Solar Telescope Ambassador Program. “These flares are among the most energetic events our star produces, and we were fortunate to catch this one under perfect observing conditions.”

Coronal loops are not new to solar physics. They arch above active regions all the time. What is new here is their size.

By combing through the sharpest images from the telescope’s Visible Broadband Imager, the team measured the loops’ widths. On average, they were about 48.2 kilometers across, with some as thin as 21 kilometers. That is smaller than many large cities on Earth and far below what previous telescopes could resolve.

The Inouye instrument can pick out details down to roughly 24 kilometers. That is more than two and a half times sharper than the next-best solar facility. In this observation, it was working right at that limit. “Knowing a telescope can theoretically do something is one thing,” said co-author and National Solar Observatory scientist Maria Kazachenko. “Actually watching it perform at that limit is exhilarating.”

Before this, theory suggested coronal loops might sit somewhere between 10 and 100 kilometers wide. No one could see them clearly enough to prove it. “We’re finally peering into the spatial scales we’ve been speculating about for years,” Tamburri said. “Now we can see it directly. These are the smallest coronal loops ever imaged on the Sun.”

The team, which includes scientists from the National Solar Observatory, the Laboratory for Atmospheric and Space Physics, the Cooperative Institute for Research in Environmental Sciences and the University of Colorado, focused on the razor-thin loops woven above the flare ribbons.

Coronal loops channel superheated plasma along magnetic field lines. When those fields twist and snap, they help power solar flares and eruptions that can send storms toward Earth. Until now, most models treated those loops as thicker tubes or bundles of many unresolved strands.

Perhaps the most exciting idea from this work is that these newly seen loops may be “elementary” structures. In other words, they could be the basic building blocks of the corona. “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.”

Getting down to this level matters. Magnetic reconnection, the process that powers flares, happens when field lines break and reconnect on very small scales. To understand where energy is stored and how it explodes outward, you need to know what those small scales look like. This observation finally gives modelers a target size to work with instead of a broad guess.

The team did not set out specifically to find ultra-fine loops. The original plan centered on another instrument, the Visible Spectropolarimeter, to study how spectral lines in the Sun’s atmosphere behave during a flare.

But the broadband imager had been running at the same time, quietly collecting its own series of images. When the researchers checked those frames, they realized the telescope had caught a flare under nearly perfect atmospheric conditions. The dark loops showed up as crisp, threadlike arcs above the bright ribbons, far clearer than anyone expected.

“We went in looking for one thing and stumbled across something even more intriguing,” Kazachenko said. The most striking images show a compact triangular flare ribbon near the center of the view and a sweeping arc-shaped ribbon near the top, all etched with delicate, dark strands that trace the magnetic field above. Even to a casual viewer, the scene looks astonishingly complex.

It is also a proof of concept for the Inouye facility itself. The telescope, funded by the National Science Foundation and operated by the National Solar Observatory, was built to push solar imaging to its limits. This is one of the first times it has done so during an X-class flare. “It’s a landmark moment in solar science,” Tamburri said. “We’re finally seeing the Sun at the scales it works on.”

The flare observed on August 8 was not just a showpiece. Flares and the storms that follow can disrupt satellites, radio communication and power grids. For people who rely on GPS, internet connections and stable electricity, space weather is no longer an abstract threat.

By resolving the smallest coronal loops ever seen, this work pushes flare models into a new regime. If scientists know the true width, shape and arrangement of the magnetic strands that carry energy, they can build more realistic simulations and test how flares grow and fade. Those models feed into space weather forecasts that help protect infrastructure on the ground and in orbit.

The study also shows the value of training a new generation of experts. Tamburri is part of the Inouye Solar Telescope Ambassador Program, which supports Ph.D. students as they learn how to process and interpret the telescope’s complex data. Their skills will spread through universities and research centers, making it easier for the broader community to use these powerful observations.

As the Sun heads through an active period in its 11-year cycle, more strong flares will erupt. Each one is a chance to point the telescope at new targets and test whether these ultra-thin loops are a common feature. If they are, solar physicists may need to rethink large parts of their playbook.

This discovery reaches beyond pure curiosity about the Sun. By resolving coronal loops down to tens of kilometers, scientists now have the first direct measurements of the small-scale magnetic structures that fuel flares. That sharper picture can improve models of when and how solar storms release energy, which in turn can lead to better space weather forecasts for satellite operators, power companies and aviation.

If the thin loops seen here are indeed the basic building blocks of the corona, future research can focus on how they twist, reconnect and break. That will help scientists pinpoint the exact scales where magnetic reconnection occurs and where dangerous particles and radiation are launched into space. Over time, this knowledge may help humanity design more resilient technology, plan safer space missions and protect astronauts and spacecraft from high-energy events.

For the research community, the result proves that the Inouye Solar Telescope can reach its theoretical resolution during real flares. That opens the door to a new wave of high fidelity studies that probe the Sun at its working scales, not just its broad outlines. It also highlights the importance of training young scientists to handle these complex data sets so that this new level of detail can be fully used in future work.

Research findings are available online in the journal The Astrophysical Journal Letters.

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