Modeling YSO Jets in 3D II: Accretion-Fed, Star-Anchored Poynting Jets in the Low-Density Polar Cavity Powered by Disk-Magnetosphere Interaction

TL;DR

This paper presents a 3D MHD simulation demonstrating how star-disk magnetic interactions generate fast, bipolar jets in young stellar objects through a cyclic load-fire-reload magnetic process, emphasizing the role of the stellar magnetosphere.

Contribution

It introduces a novel cyclic magnetic reconnection model for jet launching in YSOs, highlighting the influence of the stellar magnetosphere on bipolar outflow formation.

Findings

The magnetosphere-driven jet is faster and less dense than disk winds.

Magnetic reconnection cycles sustain continuous outflows.

Stellar magnetosphere shapes symmetric bipolar jets.

Abstract

The origin of jets in young stellar objects (YSOs) remains a subject of active investigation. We present a 3D magnetohydrodynamic simulation of jet launching in YSOs, focusing on the interaction between the stellar magnetosphere and the accretion disk. In our model, a fast, low-density bipolar jet is powered by disk-magnetosphere interaction and launched through the polar cavity that is mass-loaded from the disk rather than the star. Specifically, outflows are driven by toroidal magnetic pressure generated along "two-legged" field lines, anchored at a magnetically dominated stellar footpoint and a mass-dominated point on the (magnetically elevated) disk surface via a cyclic "load-fire-reload" process: in the "load" stage, differential rotation between stellar and disk footpoints generates toroidal magnetic pressure; in the "fire" stage, vertical gradients in the toroidal field accelerate plasma and transport Poynting flux into the polar cavity; in the "reload" stage, magnetic reconnection allows the cycle to repeat, reforming "two-legged" field lines. These field lines are not required to be fully reset to a dipolar loop configuration; it is only required that the disk-end be shallowly embedded in the (elevated) disk surface. This rapid, asynchronous process produces a continuous, large-scale outflow. The resulting magnetically dominated (Poynting) jet, accelerated by magnetic pressure within the low-density polar cavity, is distinct from the denser, slower disk wind launched through the classic magnetic-tower mechanism. Comparison with a disk-only model shows that the rotating stellar magnetosphere promotes bipolar jet launching by shaping a magnetic geometry favorable to symmetric outflows.