The recent capture of the highest-resolution images of a solar flare at the H-alpha wavelength (656.28 nm) marks a significant advancement in our understanding of the sun's magnetic architecture. This breakthrough has the potential to enhance space weather forecasting and reshape our insights into solar phenomena. Utilizing the advanced capabilities of the Daniel K. Inouye Solar Telescope (DKIST), operated by the National Solar Observatory (NSO), astronomers successfully captured unprecedented details of dark coronal loop strands during the decay phase of an X1.3-class flare on August 8, 2024.
The coronal loops observed during this event averaged 48.2 km in width, with some possibly as thin as 21 km—the smallest coronal loops ever imaged. This remarkable achievement opens new avenues for resolving the fundamental scale of solar coronal loops and pushing the limits of flare modeling into an entirely new realm. The findings are detailed in a paper titled Unveiling Unprecedented Fine Structure in Coronal Flare Loops with the DKIST, published in The Astrophysical Journal Letters.
Coronal loops are arches of plasma that follow the sun's magnetic field lines and often precede solar flares. These flares trigger sudden releases of energy when magnetic field lines twist and snap, fueling solar storms that can have significant impacts on Earth's critical infrastructure. The team at the Inouye Solar Telescope observes sunlight at the H-alpha wavelength to unveil specific features of the sun, revealing intricate details that are not visible through other solar observation methods.
This observation marks the first time that the Inouye Solar Telescope has captured an X-class flare. Cole Tamburri, the study's lead author and a Ph.D. candidate at the University of Colorado Boulder, noted, "These flares are among the most energetic events our star produces, and we were fortunate to catch this one under perfect observing conditions." The research team, which includes scientists from NSO, the Laboratory for Atmospheric and Space Physics (LASP), and the Cooperative Institute for Research in Environmental Sciences (CIRES), focused on the razor-thin magnetic field loops observed above the flare ribbons.
On average, the coronal loops measured about 48 km across, with some reaching the telescope's resolution limit. Before these observations, researchers could only speculate about the scale of these structures. "Now we can see it directly," Tamburri explained. The Inouye's Visible Broadband Imager (VBI) instrument, specially tuned to the H-alpha filter, can resolve features down to approximately 24 km, which is over two and a half times sharper than any other solar telescope.
While the original research plan focused on studying chromospheric spectral line dynamics using the Inouye’s Visible Spectropolarimeter (ViSP) instrument, the VBI data revealed unexpectedly fine coronal structures. These structures can directly inform flare models built with complex radiative-hydrodynamic codes. Maria Kazachenko, a co-author of the study and an NSO scientist, expressed excitement about making this discovery: "We went in looking for one thing and stumbled across something even more intriguing."
Theories have long suggested that coronal loops could measure anywhere from 10 to 100 km in width, yet confirming this range observationally has proven challenging—until now. "We're finally peering into the spatial scales we've been speculating about for years," Tamburri stated. This discovery not only allows for the study of the size of these loops but also their shapes, evolution, and the scales at which magnetic reconnection occurs—the engine behind solar flares.
The imagery produced from this observation is nothing short of breathtaking. Dark, thread-like loops arch elegantly in a glowing arcade, accompanied by bright flare ribbons etched in sharp relief. Even casual viewers would recognize the complexity and beauty of these structures. "It's a landmark moment in solar science," Tamburri concluded. "We're finally seeing the sun at the scales it works on."