The Sun sometimes produces flares — bright explosions that hurl streams of charged particles into space. On April 22, 2021, one such flare occurred in an active region where a dark sunspot was crossed by a bright "bridge" of hotter gas. Astronomers aimed two telescopes, one ground-based and one in space, at this spot and observed the flare with unprecedented clarity.
Inside the bright flare ribbon stretching from the light bridge, tiny clumps were hiding—"burrs," as the scientists called them. Each one measures between 233 and 895 kilometers across: that's like the distance from Moscow to Nizhny Novgorod. The clumps didn't stay put: they slid along the ribbon at speeds from 40 to 21 kilometers per second, gradually slowing down. And every six minutes, they all brightened in unison, like the heartbeat of the flare.
Where does this rhythm come from? The scientists suspect it's all about the Sun's own oscillations: its surface constantly "breathes" with a period of about five minutes. These oscillations may be nudging the process of magnetic reconnection — the very mechanism that gives birth to a flare. Magnetic ropes, twisted like cords, snap and rearrange, releasing energy in bursts. Each burst is a "burr."
If these tiny structures are indeed the elementary building blocks of flares, then by watching them, we could learn to predict space weather. After all, solar flares affect satellites, communications, and even power grids on Earth.
A light bridge in a sunspot is like a crack in ice: through it, hot gas rises from the Sun's depths, and the dark spot seems to split in two.