Magnetospheric Accretion and Ejection

Magnetospheric accretion is a universal process occurring in magnetized astronomical objects, ranging from neutron stars and white dwarfs to young stars (YSOs) and planets. In the context of neutron stars, this process is linked with phenomena such as X-ray pulsars and ultra-luminous X-ray sources (ULXs). For YSOs, it results in ultraviolet (UV) excess and atomic emission lines. Despite the wide variance in the observation energy range, the underlying physical accretion process exhibits many similarities, primarily due to the governing role of magnetic fields. Understanding these dynamical processes is essential for interpreting observational data and sheds light on the impact of accretion on star/planet evolution. We have carried out first-principle three-dimensional magnetohydrodynamic (MHD) simulations to study magnetospheric accretion. I will discuss physical insights gained from these simulations, which include filamentary accretion due to the interchange instability, magnetic bubbles similar to MAD disks, star-disk torque, field inflation, field reconnection, and episodic outflows. Finally, implications on exoplanets demographics will be discussed.