Formation and Collapse of Quiescent Cloud Cores Induced by Dynamic Compressions

TL;DR

This study uses hydrodynamical simulations to explore how molecular cloud cores form, evolve, and collapse, revealing that cores can resemble Bonnor-Ebert profiles without requiring turbulence dissipation, and that collapse occurs after a delay once a critical mass is reached.

Contribution

The paper demonstrates that quiescent, BE-like cores can form dynamically through compression and that collapse is triggered by reaching a Jeans mass, challenging turbulence dissipation theories.

Findings

Cores form with BE-like profiles but are initially non-self-gravitating.

Collapse occurs after the core reaches a critical Jeans mass.

Cores can grow in mass and size without turbulence dissipation.

Abstract

(Abridged) We present numerical hydrodynamical simulations of the formation, evolution and gravitational collapse of isothermal molecular cloud cores. A compressive wave is set up in a constant sub-Jeans density distribution of radius r = 1 pc. As the wave travels through the simulation grid, a shock-bounded spherical shell is formed. The inner shock of this shell reaches and bounces off the center, leaving behind a central core with an initially almost uniform density distribution, surrounded by an envelope consisting of the material in the shock-bounded shell, with a power-law density profile that at late times approaches a logarithmic slope of -2 even in non-collapsing cases. The resulting density structure resembles a quiescent core of radius < 0.1 pc, with a Bonnor-Ebert-like (BE-like) profile, although it has significant dynamical differences: it is initially non-self-gravitating and confined by the ram pressure of the infalling material, and consequently, growing continuously in mass and size. With the appropriate parameters, the core mass eventually reaches an effective Jeans mass, at which time the core begins to collapse. Thus, there is necessarily a time delay between the appearance of the core and the onset of its collapse, but this is not due to the dissipation of its internal turbulence as it is often believed. These results suggest that pre-stellar cores may approximate Bonnor-Ebert structures which are however of variable mass and may or may not experience gravitational collapse, in qualitative agreement with the large observed frequency of cores with BE-like profiles.