Discs and outflows in the early phases of massive star formation: influence of magnetic fields and ambipolar diffusion

TL;DR

This study uses high-resolution 3D simulations to explore how magnetic fields and ambipolar diffusion influence mass accretion, outflows, and disc formation in early massive star formation, revealing magnetic processes as key drivers.

Contribution

It provides new insights into the roles of magnetic fields and ambipolar diffusion in shaping outflows and discs during early massive star formation, using detailed numerical simulations.

Findings

Magnetic fields are the main driver of outflows up to 20 solar masses.

Disc properties vary significantly with physics included, showing opposite characteristics in ideal vs resistive models.

Magnetic processes influence early evolution, similar to low-mass star formation.

Abstract

We study mass accretion and ejection in the vicinity of massive star forming cores using high-resolution (5 au) 3D AMR numerical simulations. We investigate the mechanisms at the origin of outflows and characterise the properties of the disc forming around massive protostars. We include both protostellar radiative feedback via PMS evolutionary tracks and magnetic ambipolar diffusion. We studied 3 different cases: purely hydrodynamical, ideal MHD, and ambipolar diffusion. In the resistive models, we investigate the effects the initial amplitude of both magnetic field and rotation have on the properties of the massive protostellar system. We use simple criteria to identify the outflow and disc material and follow their evolution as the central star accretes mass up to 20 solar mass. The outflow is completely different when magnetic fields are introduced, so that magnetic processes are the main driver of the outflow up to stellar masses of ~20 solar mass. The disc properties depend on the physics included. The disc formed in the ideal and resistive runs show opposite properties in terms of plasma beta and of magnetic fields topology. While the disc in the ideal case is dominated by the magnetic pressure and the toroidal magnetic fields, the one formed in the resistive runs is dominated by the thermal pressure and has essentially vertical magnetic fields in the inner regions (R<200 au). We find that magnetic processes dominate the early evolution of massive protostellar systems (<20 solar mass) and shapes the accretion/ejection as well as the disc formation. Ambipolar diffusion is mainly at work at disc scales and regulates its properties. Our finding for the outflow and disc properties are reminiscent of low-mass star formation, suggesting that accretion and ejection in young massive and low-mass protostars are regulated by the same physical processes at the early stages.