Observational Evidence of the Role of Collisionless Magnetic Reconnection in Self- Organization of Solar and Stellar Coronae

Magnetic reconnection is widely accepted to be the driver of eruptive activity in the solar corona. However, questions about how a large amount of magnetic energy can accumulate before an eruption without triggering fast reconnection, why fast magnetic reconnection begins abruptly, and under what coronal conditions an eruption occurs remain unanswered. Observations of solar and stellar flares have revealed similar phenomenologies and power law statistics, suggesting that eruptions in solar and stellar coronae are driven by the same physical process. The existence of power law statistics has prompted the suggestion that solar and stellar coronae are self-organized, but the physical foundation of this theory has been lacking. We present observational evidence from 107 flare events in 37 sun-like stars that solar and stellar coronae self-organize into a state in which the coronal plasma is marginally collisional. This corroborates a recent model in which coronal eruptions are initiated by a catastrophic onset of collisionless magnetic reconnection [1]. These results demonstrate that the dynamics of magnetic reconnection play an active role in constraining the conditions of solar and stellar coronae. [1] P. A. Cassak, M. A. Shay, and J. F. Drake, Phys. Rev. Lett., 95, 235002 (2005).