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

Abstract

Context. Massive star formation remains one of the most challenging problems in astrophysics, as illustrated by the fundamental issues of the radiative pressure barrier and the initial fragmentation. The wide variety of physical processes involved, in particular the protostellar radiative feedback, increases the complexity of massive star formation in comparison with its low-mass counterpart. Aims. We aim to study the details of mass accretion and ejection in the vicinity of massive star forming cores using high-resolution (5 au) 3-dimensional numerical simulations. We investigate the mechanisms at the origin of outflows (radiative force versus magnetic acceleration). We characterise the properties of the disc forming around massive protostars depending on the physics included: hydrodynamics, magnetic fields, and ambipolar diffusion. Methods. We use state-of-the-art 3-dimensional adaptive-mesh-refinement models of massive dense cores collapse which integrate the equations of (resistive) grey radiation-magnetohydrodynamics, and include sink particles evolution. For the first time, we include both protostellar radiative feedback via pre-main sequence evolutionary tracks and magnetic ambipolar diffusion. To determine the role of magnetic fields and AD play in the formation of outflows and discs, we studied 3 different cases: a purely hydrodynamical run, a magnetised simulation under the ideal approximation (perfect coupling), and a calculation with ambipolar diffusion (resistive case). In the most micro-physically complex model (resistive MHD), we also investigated the effect the initial amplitude of both magnetic field and solid body rotation have on the final 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 M in most of our models. The radiative, magnetic, and hydrodynamical properties of the outflows and discs are quantitatively measured and cross compared-between models. Results. Massive stars form in all our models, together with outflows and discs. The outflow is completely different when magnetic fields are introduced, so that magneto-centrifugal processes are the main driver of the outflow up to stellar masses of 20 M . Then, the disc properties heavily depend on the physics included. In particular, the disc formed in the ideal and resistive runs show opposite properties in terms of plasma beta, i.e. the ratio of thermal to magnetic pressures, 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 a vertical magnetic fields in the inner regions (R < 100 − 200 au). Conclusions. We find that magnetic processes dominate the early evolution of massive protostellar systems (M < 20 M ) and shapes the accretion/ejection as well as the disc formation. Ambipolar diffusion is mainly at work at disc scales and regu...

Influence of magnetic field and stellar radiative feedback on the collapse and the stellar mass spectrum of a massive star-forming clump

“…When non-ideal MHD, i.e. ambipolar diffusion, is included the scheme is the one described in Masson et al (2012) and used in previous studies (Masson et al 2016;Hennebelle et al 2020b;Mignon-Risse et al 2021;Commerçon et al 2021;Lebreuilly et al 2021). The resistivities are the ones calculated in Marchand et al (2016).…”

“…The simulations were performed with the adaptive mesh refinement (AMR) magnetohydrodynamics (MHD) code RAMSES (Teyssier 2002;Fromang et al 2006). When non-ideal MHD, namely, ambipolar diffusion, is included the scheme, as described in Masson et al (2012) and used in previous studies (Masson et al 2016;Hennebelle et al 2020b;Mignon-Risse et al 2021;Commerçon et al 2021;Lebreuilly et al 2021). The resistivities are the ones calculated in Marchand et al (2016).…”

A Massive Star is Born: How Feedback from Stellar Winds, Radiation Pressure, and Collimated Outflows Limits Accretion onto Massive Stars

“…In contrast, the influence of magnetic fields reduces disk formation due to magnetic braking as shown in Figure 8, which shows thin density projections of the dense circumstellar material, as a function of primary stellar mass, that surround the primary star along its equatorial plane for runs ROFµ φ 2 (top row) and ROFWµ φ 2 (bottom row). Rosen & Krumholz (2020) showed that magnetic braking, which removes angular momentum from the infalling material as the core collapses inhibits the formation of a discernible accretion disk around the massive star, however higher resolution and non-ideal MHD effects such as ambipolar diffusion and Ohmic re-sistivity may reduce how much angular momentum is removed leading to smaller accretion disks than those produced when magnetic fields are not included (e.g., Zhao et al 2020;Mignon-Risse et al 2021;Commerçon et al 2021). Such effects are not explored in this work.…”