Collapse of a molecular cloud core to stellar densities: the formation and evolution of pre-stellar discs

TL;DR

This study uses radiation hydrodynamical simulations to explore the collapse of molecular cloud cores, revealing the formation and evolution of pre-stellar discs, their lifetimes, and potential for binary formation, with implications for observations.

Contribution

It demonstrates that realistic physics extends pre-stellar disc lifetimes and influences their properties, providing new insights into early star formation stages.

Findings

Pre-stellar discs can last 1.5-3 times longer with realistic physics.

Massive pre-stellar discs up to 0.22 Msun can form and last several thousand years.

Collapse triggers shock waves and bipolar outflows without magnetic fields.

Abstract

We report results from radiation hydrodynamical simulations of the collapse of molecular cloud cores to form protostars. The calculations follow the formation and evolution of the first hydrostatic core/disc, the collapse to form a stellar core, and effect of stellar core formation on the surrounding disc and envelope. Past barotropic calculations have shown that rapidly-rotating first cores evolve into `pre-stellar discs' with radii up to ~100 AU that may last thousands of years before a stellar core forms. We investigate how the inclusion of a realistic equation of state and radiative transfer alters this behaviour, finding that the qualitative behaviour is similar, but that the pre-stellar discs may last 1.5-3 times longer in the more realistic calculations. The masses, radii, and lifetimes of the discs increase for initial molecular cloud cores with faster rotation rates. In the most extreme case we model, a pre-stellar disc with a mass of 0.22 Msun and a radius of ~100 AU can form in a solar-mass cloud and last several thousand years before a stellar core is formed. Such large, massive objects may be imaged using ALMA. Fragmentation of these massive discs may also provide an effective route to binary and multiple star formation, before radiative feedback from accretion onto the stellar core can inhibit fragmentation. Once collapse to form a stellar core occurs within the pre-stellar disc, the radiation hydrodynamical simulations produce qualitatively different behaviour from the barotropic calculations due to the accretion energy released. This drives a shock wave through the circumstellar disc and launches a bipolar outflow even in the absence of magnetic fields.