Recently, Associate Researcher HONG Junchao and collaborators from the Yunnan Observatories of the Chinese Academy of Sciences reported the first direct observational evidence of oscillatory magnetic reconnection in a solar coronal bright point (CBP). This finding provides a key clue to understanding the mechanisms of energy release in small-scale solar structures and the long-standing puzzle of coronal heating. The results were published in The Astrophysical Journal.
Coronal bright points are small-scale, localized regions of enhanced emission distributed throughout the solar corona. With typical diameters below 30 arcseconds, they consist of miniature coronal loops and generally last for several hours. Despite their diminutive size, CBPs are closely tied to magnetic energy release and are regarded as ‘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 prevalent in astrophysical plasmas, involving the rapid conversion of magnetic energy as the magnetic field topology is suddenly rearranged. Oscillatory magnetic reconnection is a special mode of this process, characterized by periodic switching of inflow and outflow regions during reconnection. The global magnetic configuration remains largely unchanged, while magnetic energy is released rhythmically in a “sawtooth” or “tug-of-war” fashion. Until now, this phenomenon had been primarily confined to theoretical models and numerical simulations, lacking direct observational support.
Using extreme-ultraviolet (EUV) imaging data from the Solar Orbiter spacecraft on 10 April 2023 at a heliocentric distance of 0.293 astronomical units (AU; ~43.8 million kilometres), the research team identified two phases of current sheet evolution in a coronal bright point (CBP) within a quiet-Sun region. Phase 1 showed a current sheet (C1) extending to ~2.4 Mm over 10 minutes before collapsing into a magnetic null point; Phase 2 began ~3 minutes later, with a second current sheet (C2) forming perpendicular to C1 and growing to ~4 Mm before fading.
Both phases were accompanied by noticeable plasma flows and heating. Remarkably, the CBP’s brightness correlated closely with the length changes of C1 and C2, exhibiting a ~20-minute decaying oscillation pattern—strongly evidence of rhythmic conversion of magnetic energy into thermal and kinetic energy, a hallmark of oscillatory reconnection.
This discovery significantly advances the understanding of energy release in small-scale solar structures. The research team notes that oscillatory reconnection may act as a ‘magnetic internal engine’, delivering steady, rhythmic energy input without disturbing the global magnetic topology, and could represent a fundamental heating mechanism not only for CBPs but also for other stable small-scale coronal features. Future studies will focus on identifying additional cases and statistically evaluating the prevalence of this process across the Sun.
This work was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences, the National Natural Science Foundation of China, the Yunnan Province “Xingdian Talent” Program, the CAS “Western Light” Talent Program, and the Yunnan Revitalization Talent Support Program.
Figure 1, 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 HONG.
Figure 2. Temporal evolution of coronal bright point brightness in multiple passbands (green: AIA 193 Å; black: EUI 174 Å; blue: AIA 171 Å), and the corresponding current sheet length (pink dots). Image by HONG.
Contact:
HONG Junchao
Yunnan Observatories, CAS
E-mail: hjcsolar@ynao.ac.cn
