A sunspot, a dark island on the scorching surface, breathes. Every three minutes, a wave spreads from it, runs along an invisible magnetic arch, and makes the plasma above a neighboring spot flare with a radio signal. Radio telescopes caught seven such flares in a row on February 14, 2024.
The chain of bursts repeated with a period of about 160 seconds. The arches connected two groups of sunspots, and the spots themselves oscillated with a period of roughly 170 seconds. The bursts were strongly polarized and hot, and new magnetic field was emerging nearby. All this fits into a picture: slow magnetic waves from the spots set the rhythm for the radio emission.
The frequencies of the bursts changed smoothly, reflecting how the plasma density decreases along the arch. This confirms that the radio emission is born in the plasma itself, not elsewhere. The Sun turned out to be not just a boiling cauldron but a precise metronome, beating time with magnetic waves.
Sunspots are darker than the surrounding surface because the strong magnetic field prevents hot plasma from rising — the spot is cooler by a couple of thousand degrees.
In Arthur C. Clarke's story "The Solar Wind," giant solar flares threaten spacecraft, a reminder that the Sun's rhythms can be deadly.