How External Medium outside Prestellar Cores Affects Protostellar Growth: Variations in Accretion Rate and Evolution of Disks and Outflows

TL;DR

This study uses 3D magnetohydrodynamic simulations to show how the external environment's density influences protostellar growth, disk evolution, and outflow dynamics, revealing environment-dependent star formation efficiencies and angular momentum transport mechanisms.

Contribution

It demonstrates how external medium density affects accretion, disk development, and outflow behavior, providing new insights into environmental regulation of star formation processes.

Findings

Higher external density leads to Bondi-like accretion.

Dense environments can produce star formation efficiencies exceeding unity.

External medium influences disk growth and outflow duration.

Abstract

We investigate how the external medium surrounding prestellar cores affects the star formation process by conducting three-dimensional resistive magnetohydrodynamic simulations. The initial cores follow critical Bonnor-Ebert profiles and are embedded in environments with different ambient densities. The simulations follow the evolution at least until the envelope mass within a radius equal to twice the critical Bonnor-Ebert radius drops to 35% of the initial cloud mass. We reveal that in environments with higher external density, enhanced mass inflow from the envelope leads to Bondi-like accretion as the protostellar mass increases. The continued inflow substantially increases the final stellar mass, resulting in star formation efficiencies that appear to exceed unity in dense environments. The external medium also influences the evolution of circumstellar disks and protostellar outflows: with the high-density external medium, disks grow rapidly but their mass becomes smaller relative to the protostellar mass, and the outflow is sustained over a long duration. However, the ratio of angular momentum removed by outflows and magnetic braking to that introduced by inflowing gas decreases with increasing external density. These results suggest that the density of the external medium regulates not only protostellar mass growth but also the inflow-outflow balance and angular momentum transport in magnetized, rotating star-forming cores.