Formation and evolution of protostellar accretion discs – I. Angular-momentum budget, gravitational self-regulation, and numerical convergence
| Autor: | Wenrui Xu, Matthew W. Kunz |
|---|---|
| Rok vydání: | 2021 |
| Předmět: |
Angular momentum
FOS: Physical sciences Astrophysics::Cosmology and Extragalactic Astrophysics Astrophysics 01 natural sciences Specific relative angular momentum law.invention law 0103 physical sciences Astrophysics::Solar and Stellar Astrophysics Protostar 010303 astronomy & astrophysics Solar and Stellar Astrophysics (astro-ph.SR) Astrophysics::Galaxy Astrophysics Earth and Planetary Astrophysics (astro-ph.EP) Physics 010308 nuclear & particles physics Ambipolar diffusion Astronomy and Astrophysics Torus Astrophysics - Astrophysics of Galaxies Accretion (astrophysics) Astrophysics - Solar and Stellar Astrophysics Space and Planetary Science Astrophysics of Galaxies (astro-ph.GA) Astrophysics::Earth and Planetary Astrophysics Hydrostatic equilibrium Magnetohydrodynamics Astrophysics - Earth and Planetary Astrophysics |
| Zdroj: | Monthly Notices of the Royal Astronomical Society. 502:4911-4929 |
| ISSN: | 1365-2966 0035-8711 |
| Popis: | We investigate the formation and early evolution of a protostellar disc from a magnetized pre-stellar core using non-ideal magnetohydrodynamic (MHD) simulations including ambipolar diffusion and Ohmic dissipation. The dynamical contraction of the pre-stellar 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 $\sim$30 au in diameter at $\sim$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 $Q\sim 1$-$2$), 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. Comment: 20 pages, 21 figures; accepted by MNRAS |
| Databáze: | OpenAIRE |
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