Protostellar Jet and Outflow in the Collapsing Cloud Core

TL;DR

This study uses resistive MHD simulations to distinguish the driving mechanisms and characteristics of low-velocity outflows and high-velocity jets in star-forming collapsing cloud cores, revealing their origins and magnetic field configurations.

Contribution

It demonstrates that outflows and jets originate from different cores with distinct magnetic field structures and driving forces, providing new insights into star formation processes.

Findings

Low-velocity outflows driven by magnetocentrifugal mechanism from the adiabatic core.

High-velocity jets driven by magnetic pressure gradient from the protostar.

Different magnetic field configurations influence flow collimation and velocity.

Abstract

We investigate the driving mechanism of outflows and jets in star formation process using resistive MHD nested grid simulations. We found two distinct flows in the collapsing cloud core: Low-velocity outflows (sim 5 km/s) with a wide opening angle, driven from the first adiabatic core, and high-velocity jets (sim 50 km/s) with good collimation, driven from the protostar. High-velocity jets are enclosed by low-velocity outflow. The difference in the degree of collimation between the two flows is caused by the strength of the magnetic field and configuration of the magnetic field lines. The magnetic field around an adiabatic core is strong and has an hourglass configuration. Therefore, the low-velocity outflow from the adiabatic core are driven mainly by the magnetocentrifugal mechanism and guided by the hourglass-like field lines. In contrast, the magnetic field around the protostar is weak and has a straight configuration owing to Ohmic dissipation in the high-density gas region. Therefore, high-velocity jet from the protostar are driven mainly by the magnetic pressure gradient force and guided by straight field lines. Differing depth of the gravitational potential between the adiabatic core and the protostar cause the difference of the flow speed. Low-velocity outflows correspond to the observed molecular outflows, while high-velocity jets correspond to the observed optical jets. We suggest that the protostellar outflow and the jet are driven by different cores (the first adiabatic core and protostar), rather than that the outflow being entrained by the jet.