On August 8, 2024, the NSF Daniel K. Inouye Solar Telescope in Hawaii achieved a historic milestone by capturing the sharpest images ever taken of a solar flare. The unprecedented observations revealed coronal loops in stunning detail. The arches of superheated plasma following the Sun’s magnetic field lines were captured at such resolution that it’s possible to see individual structures as narrow as 21 kilometres across.
To put this achievement into perspective, these plasma loops are roughly twice the width of Los Angeles, yet they arch through space in formations that span distances equivalent to several Earth diameters. The Inouye telescope’s space piercing resolution is more than 2.5 times sharper than any previous solar telescope, finally allowing astronomers to peer into the fundamental building blocks of solar flares.
The NSF Daniel K. Inouye Solar Telescope has a 4.24-meter primary mirror in an off-axis configuration to minimise scattered sunlight. It requires over 11 kilometre of coolant piping for its active cooling systems to handle the extreme heat of direct solar observation, while adaptive and active optics systems use sensors and actuators to continuously correct for atmospheric disturbances and maintain precise mirror alignment. Ten mirrors guide sunlight throughout the observatory to four instruments designed for solar imaging and magnetic field measurements.
The Hawaiian Observatory, home to the NSF Daniel K. Inouye Solar Telescope, on the summit of Haleakalā volcano (Credit : Ekrem Canli)
The discovery came almost by accident. Cole Tamburri, a PhD student at the University of Colorado Boulder and the study’s lead author, was conducting routine observations when the X1.3-class flare erupted.
“This is the first time the Inouye Solar Telescope has ever observed an X-class flare. These flares are among the most energetic events our star produces, and we were fortunate to catch this one under perfect observing conditions,” – Cole Tamburri from University of Colorado Boulder
The telescope’s Visible Broadband Imager, tuned to capture light at a specific wavelength emitted by hydrogen atoms, revealed dark threadlike loops arching through the Sun’s corona with breathtaking clarity. The team measured loop widths averaging 48.2 kilometres, with some potentially half as narrow. These measurements represent the smallest coronal loops ever imaged.
According to Tamburri, the experience resembles going from seeing a forest to suddenly seeing every single tree. The imagery reveals dark, threadlike loops arching in glowing arcades, with bright flare ribbons etched in almost impossibly sharp relief, including a compact triangular formation near the centre and a sweeping arc across the top.
A high resolution image of the flare from the Inouye Solar Telescope, taken on August 8, 2024, at 20:12 UT. The image is about 4 Earth diameters on each side. (Credit : NSF/NSO/AURA)
For decades, theories suggested coronal loops could range from 10 to 100 kilometres in width, but confirming this observationally had been impossible until now. It finally opens the door to studying not just the sheer size of the loops but their shapes, evolution, and even the scales where magnetic reconnection, the engine behind flares, occurs.
Solar flares are among the most dangerous space weather events, capable of disrupting satellites, power grids, and communications on Earth. By understanding the structure and processes that are behind these phenomena it may just be possible to improve the models that predict when and how solar storms will impact our technology dependent world.
Perhaps most tantalising is the possibility that these newly resolved structures are elementary building blocks, the fundamental components of flare architecture. If confirmed, this discovery would mark a paradigm shift in solar physics, allowing scientists to study individual magnetic loops rather than just bundles of them.
Source : The NSF Inouye Solar Telescope Observes Its First X-Class Solar Flare and Reveals the Smallest Coronal Loops Ever Imaged