The Approach to Collapse of Molecular Clouds

TL;DR

This paper investigates how molecular cloud cores, which are crucial for star formation, evolve through oscillations and gravitational instability, revealing a slow contraction phase that may explain observed spectral signatures.

Contribution

It introduces a perturbation theory analysis of oscillating spherical clouds at the brink of collapse, highlighting a prolonged subsonic contraction phase.

Findings

Clouds undergo subsonic, accelerating contraction near instability

Oscillations do not prevent collapse but influence contraction dynamics

The slow contraction may explain spectral infall signatures in starless cores

Abstract

The dense molecular cloud cores that form stars, like other self-gravitating objects, undergo bulk oscillations. Just at the point of gravitational instability, their fundamental oscillation mode has zero frequency. We study, using perturbation theory, the evolution of a spherical cloud that possesses such a frozen mode. We find that the cloud undergoes a prolonged epoch of subsonic, accelerating contraction. This slow contraction occurs whether the cloud is initially inflated or compressed by the oscillation. The subsonic motion described here could underlie the spectral infall signature observed in many starless dense cores.