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Using the world's largest solar telescope, a team of scientists has captured one of the most detailed views ever of a microflare—a small yet powerful solar explosion. The images are helping scientists understand the complexity of magnetic fields powering the sun's smallest outbursts.

The new research, led by Dr. João da Silva Santos, a postdoctoral researcher at the U.S. National Science Foundation (NSF) National Solar Observatory (NSO), uses unparalleled data from the NSF Daniel K. Inouye Solar Telescope, built and operated by the NSO on Maui, to reveal how magnetic fields deep in the sun's lower atmosphere can suddenly reconnect and unleash bursts of energy, heat, and plasma—an explosive process known as magnetic reconnection.

The research was last month in the The Astrophysical Journal by a team of scientists at two organizations: the NSF National Solar Observatory and the NSF National Center for Atmospheric Research (NSF NCAR).

"This study investigates a small yet powerful event on the sun where magnetic fields reconnected in the solar atmosphere," says da Silva Santos. "We captured a microflare in extraordinary detail, observing sudden heating, fast-moving plasma, and turbulent motions in a region just over 700 kilometers wide, yet showing substructures 10 times smaller than that."

Although the event was tiny when compared to massive solar flares—i.e., "average" flares are about 100–1,000 times stronger—its energy release was far from insignificant, and estimated to be on the order of 10 billion lightning bolts.

This event, which initially displays characteristics typical of Ellerman bombs before evolving into a more complex microflare, was observed in high resolution using two of the Inouye's instruments: the Visible Broadband Imager (VBI) and the Visible Spectro-Polarimeter (ViSP). The impressive telescope capabilities revealed remarkable details such as sudden bursts of light, fast plasma flows, and fine-scale magnetic field interactions unfolding just hundreds of kilometers above the solar surface.

The data show the brightening occurred in a tightly packed zone where opposite magnetic fields met and canceled out, releasing energy in the process. Spectropolarimetric analysis using complex modeling allowed the team to extract precise temperature, velocity, and turbulence profiles, and reconstruct the 3D magnetic topology of the region.

"We found that the reconnection occurred along a dome-shaped magnetic structure known as a fan-spine configuration, complete with a magnetic null point and enhanced squashing factors," said Robert Jarolim, NSF NCAR scientist and co-author of the study. "This had been predicted in simulations and hinted at in coarser observations, but now we could see it clearly."

The structure acted like a trap and trigger, guiding the release of energy through the cancellation of magnetic fields and the sudden acceleration of plasma—akin to snapping rubber bands in a "magnetic" net.

Eric Dunnington, an undergraduate student from the Rensselaer Polytechnic Institute, played a key role in the study and is also a co-author. In the summer of 2024, he participated in the NSF Research Experiences for Undergraduates program run by the Boulder Solar Alliance, and had Dr. da Silva Santos as a mentor.

"João offered me the invaluable opportunity to significantly contribute to the data calibration and early analysis, and even to present a poster with preliminary results at the American Geophysical Union 2024 annual meeting in Washington, D.C.," Dunnington says. "It's a fantastic example of how undergraduate research can directly advance cutting-edge science."

The findings address longstanding questions about how small-scale reconnection works in the upper photosphere and low chromosphere, regions of the solar atmosphere that are notoriously difficult to observe. While larger solar flares have been widely studied, these microflares are more elusive—yet potentially just as important for understanding how the sun's energy ultimately affects the space environment around Earth.

"This research provides some of the clearest observational evidence to date that magnetic reconnection can occur in compact, low-lying magnetic structures," says da Silva Santos. "And without the Inouye's resolution, the key small-scale features would have remained invisible."

This study not only opens a new window into the sun's hidden activity, but also strengthens the case that even small-scale solar events could play a role in understanding stronger ones driving space weather. And thanks to the NSF Inouye Solar Telescope, the smallest sparks on the sun are no longer out of reach.