A recent study led by Dr. HONG Junchao from the Yunnan Observatories of the Chinese Academy of Sciences (CAS) reported the first direct observational evidence of oscillatory magnetic reconnection in a solar coronal bright point (CBP). This study, published in The Astrophysical Journal, provides insights into the mechanisms of energy release in small-scale solar structures and addresses the long-standing puzzle of coronal heating.

Coronal bright points are small, localized regions in the solar corona that exhibit enhanced emission. Typically, they have diameters of less than 30 arcseconds and consist of miniature coronal loops, lasting for several hours. Despite their small size, CBPs are closely linked to magnetic energy release and are considered "micro active regions" on the solar surface, making them ideal targets for studying solar magnetic activity and localized heating.

Magnetic reconnection is a fundamental physical process in astrophysical plasmas, involving the rapid conversion of magnetic energy as the magnetic field's topology suddenly changes. Oscillatory magnetic reconnection is a specific mode of this phenomenon, characterized by periodic switching between inflow and outflow regions during reconnection. In this case, the overall magnetic configuration remains largely unchanged while magnetic energy is released rhythmically in a "sawtooth" or "tug-of-war" manner. Until now, this phenomenon had primarily existed in theoretical models and numerical simulations, lacking direct observational evidence.

To investigate this process, the researchers used extreme-ultraviolet (EUV) imaging data from the Solar Orbiter spacecraft on April 10, 2023, at a heliocentric distance of 0.293 astronomical units (approximately 43.8 million kilometers) to identify two phases of current sheet evolution in a CBP located in a quiet-Sun region. In Phase 1, a current sheet (C1) extended approximately 2.4 megameters over 10 minutes before collapsing into a magnetic null point. Phase 2 began roughly three minutes later, with a second current sheet (C2) forming perpendicularly to C1 and growing to about four megameters before fading.

Both phases were accompanied by noticeable plasma flows and heating. Significantly, the brightness of the CBP correlated closely with the length changes of C1 and C2, exhibiting a decaying oscillation pattern over approximately 20 minutes. This supports the idea of rhythmic conversion of magnetic energy into thermal and kinetic energy, a defining feature of oscillatory reconnection.

This discovery enhances the understanding of energy release in small-scale solar structures. The research team suggests that oscillatory reconnection may act as a "magnetic internal engine," providing steady, rhythmic energy input without disrupting the global magnetic topology. This mechanism could be fundamental not only for CBPs but also for other stable small-scale features in the solar corona.

This work received support from the Strategic Priority Research Program of CAS and the National Natural Science Foundation of China, among other sources.

EUV 174 Å image from Solar Orbiter, showing a coronal bright point (CBP) and the observed oscillatory magnetic reconnection process. Magnetic reconnection reverses from current sheet C1 to C2, indicating a transition in inflow–outflow directions. (Image by Dr. HONG Junchao)