Ultrafast Measurements of Whistler Waves in Electron-only Magnetic Reconnection

Magnetic reconnection, a fundamental energy conversion process, underpins a multitude of eruptive phenomena across the universe. Compared to the traditional standard magnetic reconnection with ion coupling, the recently discovered electron-only magnetic reconnection operates at strikingly diminutive spatial scales, imposing formidable observational constraints on resolving its intrinsic physical processes, most critically within its core region—near the X-line. Consequently, the intrinsic mechanism governing electron-only magnetic reconnection remains largely enigmatic. Leveraging high-resolution data from NASA’s MMS mission, we present unprecedented observations of two types of whistler waves in electron-only magnetic reconnection: right-handed whistler waves near the X-line, excited by perpendicular anisotropy electron distributions via second order cyclotron resonance, contrasted by left-handed whistler waves in the outflow jet. The outflow-associated whistler waves reside within a magnetic hole coupled to the Hall magnetic field. Beyond these distinct features diverging from standard magnetic reconnection, hallmark phenomena analogous to standard magnetic reconnection—specifically flux pileup region in the outflow—is also identified for the first time in this electron-only regime. Our observations may provide novel insights into the magnetic reconnection and the microscale dynamics in space and astrophysical plasmas.