Sometimes bright loops flash on the Sun — solar flares. They resemble giant electric discharges, but instead of wires, there are magnetic fields. Inside an active region, magnetic lines tangle like threads in a ball, and when they snap and reconnect, energy is released. In this work, scientists found the exact spot where this happens.

They studied a medium-sized flare (class M2.1) in active region NOAA 12268. First, they reconstructed the magnetic field before the flare from observational data. It turned out that above the flare region there is a special structure — a hyperbolic flux tube of curved magnetic field. This is a place where magnetic lines converge and diverge, like water in a funnel. Nearby, at the base, there are two layers where the field changes particularly sharply — quasi-separatrix layers.

Then the scientists ran a computer simulation that mimics the behavior of plasma and the magnetic field. In the simulation, a thin current sheet formed inside the hyperbolic flux tube, where magnetic lines of opposite direction met and reconnected. Simultaneously, at the base, field lines began to slip along those very layers: this is called slipping reconnection. According to the authors, it was this that triggered the main reconnection in the tube.

As a result, the reconnection energy flowed downward to the Sun's surface and ignited bright ribbons — the very flare ribbons seen in telescopes. So the chain is: first slipping reconnection at the base, then main reconnection in the hyperbolic flux tube, and that gives the flare's light.

It's like first giving a slight tug on the threads in a ball, and then the whole ball suddenly rearranges and releases energy. Understanding such details helps better predict solar flares, which affect space weather and our technology.