2021/01/31 by Wenrui Xu, Matthew W. Kunz
Chemistry · Physics and Astronomy · #Accretion (finance) #Ambipolar diffusion #Angular momentum #Angular momentum coupling #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Classical mechanics #Gravitational collapse #Hydrostatic equilibrium #Magnetic field #Magnetohydrodynamics #Molecular Spectroscopy and Structure #Physics #Plasma #Protostar #Specific relative angular momentum #Star formation #Stars #Stellar, planetary, and galactic studies #Total angular momentum quantum number #astro-ph.EP #astro-ph.GA #astro-ph.SR
paper · pdf · doi:10.1093/mnras/stab314
20 pages, 21 figures; accepted by MNRAS
openalex created_date 2021/01/18 · arxiv created 2021/02/01 · openalex publication_date 2021/02/04 · arxiv updated 2021/02/17 · openalex updated_date 2026/08/05
ABSTRACT We investigate the formation and early evolution of a protostellar disc from a magnetized prestellar core using non-ideal magnetohydrodynamic (MHD) simulations including ambipolar diffusion and Ohmic dissipation. The dynamical contraction of the prestellar core ultimately leads to the formation of a first hydrostatic core, after ambipolar diffusion decouples the magnetic field from the predominantly neutral gas. The hydrostatic core accumulates angular momentum from the infalling material, evolving into a rotationally supported torus; this ‘first hydrostatic torus’ then forms an accreting protostar and a rotationally supported disc. The disc spreads out by gravitational instability, reaching ∼30 au in diameter at ∼3 kyr after protostar formation. The total mass and angular momentum of the protostar–disc system are determined mainly by accretion of gas from an infalling pseudo-disc, which has low specific angular momentum because of magnetic braking; their removal from the protostar–disc system by outflow and disc magnetic braking are negligible, in part because the magnetic field is poorly coupled there. The redistribution of angular momentum within the protostar–disc system is facilitated mainly by gravitational instability; this allows formation of relatively large discs even when the specific angular momentum of infalling material is low. We argue that such discs should remain marginally unstable as they grow (with Toomre Q ∼ 1–2), an idea that is broadly consistent with recent observational estimates for Class 0/I discs. We discuss the numerical convergence of our results, and show that properly treating the inner boundary condition is crucial for achieving convergence at an acceptable computational cost.