Modeling YSO Jets in 3D I: Highly Variable Asymmetric Magnetic Pressure-Driven Jets in the Polar Cavity from Toroidal Fields Generated by Inner Disk Accretion

TL;DR

This paper uses 3D MHD simulations to reveal a new magnetic pressure-driven jet mechanism in YSOs, showing variability and asymmetry, and challenging traditional magneto-centrifugal models.

Contribution

It introduces a novel magnetic pressure-driven jet mechanism powered by toroidal fields, differing from classical models, and highlights jet variability and asymmetry in YSO simulations.

Findings

Jet driven by toroidal magnetic pressure in polar funnel

Magnetic tension does not contribute to jet acceleration

Jet exhibits strong spatial and temporal variability

Abstract

Jets and outflows are commonly observed in young stellar objects (YSOs), yet their origins remain debated. Using 3D non-ideal magnetohydrodynamic (MHD) simulations of a circumstellar disk threaded by a large-scale open poloidal magnetic field, we identify three components in the disk-driven outflow: (1) a fast, collimated jet, (2) a less collimated, slower laminar disk wind, and (3) a magneto-rotational instability (MRI)-active turbulent disk wind that separates the former two. At high altitudes, the MRI-active wind merges with the laminar disk wind, leaving only the jet and disk wind as distinct components. The jet is powered by a novel mechanism in the star formation context: a lightly mass-loaded outflow driven by toroidal magnetic pressure in the low-density polar funnel near the system's rotation axis. A geometric analysis of the magnetic field structure confirms that magnetic tension does not contribute to the outflow acceleration, with magnetic pressure acting as the dominant driver. While the outflow in our model shares similarities with the magneto-centrifugal model-such as angular momentum extraction from the accreting disk-centrifugal forces play a negligible role in jet acceleration. In particular, the flow near the jet base does not satisfy the conditions for magneto-centrifugal wind launching. Additionally, the jet in our simulation exhibits strong spatial and temporal variability. These differences challenge the applicability of rotation-outflow velocity relations derived from steady-state, axisymmetric magneto-centrifugal jet models for estimating the jet's launching radius. For the slower disk wind, vertical motion is driven by toroidal magnetic pressure, while centrifugal forces widen the wind's opening angle.