A quantification of the non-spherical geometry and accretion of collapsing cores

TL;DR

This study uses high-resolution simulations to classify the complex, filamentary structures of collapsing cores in molecular clouds, revealing that most cores are irregular and that accretion is highly anisotropic, challenging spherical models.

Contribution

It provides the first detailed classification of core geometries in simulations, emphasizing the importance of filamentary accretion and non-spherical shapes in star formation.

Findings

Most cores are irregular filaments rather than spheres.

Accretion occurs primarily along filaments outside the core.

Spherical symmetry assumptions are invalid for most collapsing cores.

Abstract

We present the first detailed classification of the structures of Class 0 cores in a high resolution simulation of a giant molecular cloud. The simulated cloud contains 10^4 solar masses and produces over 350 cores which allows for meaningful statistics. Cores are classified into three types according to how much they depart from spherical symmetry. We find that three quarters of the cores are better described as irregular filaments than as spheres. Recent Herschel results have shown that cores are formed within a network of filaments, which we find has had a significant impact on the resulting core geometries. We show that the column densities and ram pressure seen by the protostar are not uniform and generally peak along the axes of the filament. The angular momentum vector of the material in the cores varies both in magnitude and direction, which will cause the rotation vector of the central source to fluctuate during the collapse of the core. In the case of the more massive stars, accretion from the environment outside the original core volume is even more important than that from the core itself. This additional gas is primarily accreted onto the cores along the dense filaments in which the cores are embedded, and the sections of the surfaces of the cores which do not coincide with a filament have very little additional material passing through them. The assumption of spherical symmetry cannot be applied to the majority of collapsing cores, and is never a good description of how stars accrete gas from outside the original core radius. This has ramifications for our understanding of collapsing cores, in particular their line profiles, the effect of radiation upon them and their ability to fragment.