The birth of protostars is a complex and multi-scale process that requires robust numerical simulations.
We aim to model the birth and evolution of low-mass protostars and the circum-stellar disks that surround them. Understanding the physics at these small scales is of importance to properly model the feedback effects the protostars have on larger scales.
To this end, we use the 3D adaptive mesh refinement code RAMSES to carry out a set of radiation hydrodynamics simulations of the birth of low-mass protostars with a resolution never achieved before (1.4e-4 AU at max. refinement level, 20-1000 cells per jeans length). We carry out both spherically symmetrical collapse calculations, and asymmetrical collapses using initial turbulence in the cloud core.
Owing to our very high resolution, we were able to resolve convective motions within the protostar. We find that protostars are convective from the moment of inception, despite their radiative stability, due to the energy injected by accretion. The radius swells over time as the shock radiates an inconsequential fraction of the incoming accretion energy. A power-law relationship between pre-stellar luminosity and radius is revealed.
In asymmetrical collapses, the protostar is embedded within its disk, exhibiting solid body rotation whereas the disk is in near-Keplerian motion. The density distribution is characterized by a plateau in the inner regions (i.e, < 1e-2 AU) and a power-law envelope for the disk. The accretion shock envelops both the protostar and the disk, and its asymmetrical structure facilitates the escape of radiation. The star-disk structure expands rapidly over time.
These results shed some light on an otherwise poorly understood phase in the stellar formation process. Although the simulated time is short (of the order of hundreds of days), it is our hope that these results can be used to infer the behavior across larger timescales.