The Cosmic Bell: How Pulsations from the Sun to Stars Fade Away ✛
The Sun is constantly struck by blows — magnetic reconnection in the plasma releases energy, making the corona flare up. After each such blow, magnetohydrodynamic waves linger in the plasma loops, like the fading ring of a bell. It is this cosmic chime, quasi-periodic pulsations, that a team of researchers captured by analyzing two and a half thousand events on the Sun.
Among them were tiny EUV brightenings, brief bursts of extreme ultraviolet spanning about a hundred kilometers, and full-fledged flares of classes C, M, and X. Using photometry and empirical mode decomposition, they extracted damped sinusoids from the light curves. Then Bayesian regression and Fourier analysis confirmed: significant pulsations were found in 185 micro-brightenings and 89 flares. Their periods and damping times fell on a single line in a log-log plot. The law turned out to be universal: τ ∝ P^α, with α ≈ 0.87–0.92.
The universal power law points to a common damping mechanism. Most likely, magnetohydrodynamic waves, either kink modes or slow magnetoacoustic waves, are responsible. For physics, this is a gift: pulsations become a “ruler” and a “thermometer.” From the oscillation period, one can infer the temperature or length of the plasma loop — parameters that are nearly impossible to measure directly. This is especially valuable for micro-events and distant stars: on red dwarfs, loops are indistinguishable with telescopes, but their pulsations can now reveal details about magnetic fields and coronal heating. Such an approach promises new insights into stellar evolution — from quiescent phases to violent flare cycles.
Looking ahead, multiwavelength observations (for example, ultraviolet together with X-rays) will allow distinguishing wave types, and new-generation spectrographs will refine the physics of damping. Thus, statistics from thousands of flares will turn into an automatic diagnostic of plasma structures. Then the cosmic bell will ring not as a metaphor but as a precise instrument: by its chime, astrophysicists will be able to determine what lies hidden in the fiery heart of a star.
EUV brightenings last from a few seconds to minutes and are only about 100 km across, yet they exhibit the same pulsations as giant flares spanning tens of thousands of kilometers.