Embedded Oscillating Starless Cores

TL;DR

This paper investigates the damping of non-radial oscillations in starless cores, showing that such oscillations can persist for hundreds of thousands of years, affecting interpretations of their dynamical states.

Contribution

It introduces a model analyzing how external density influences oscillation damping rates, combining numerical and analytical approaches for starless cores.

Findings

Oscillations can last hundreds of thousands of years in dense environments.

External medium density significantly affects damping rates.

Oscillations may mimic other dynamical processes like rotation or collapse.

Abstract

In a previous paper we demonstrated that non-radial hydrodynamic oscillations of a thermally-supported (Bonnor-Ebert) sphere embedded in a low-density, high-temperature medium persist for many periods. The predicted column density variations and molecular spectral line profiles are similar to those observed in the Bok globule B68 suggesting that the motions in some starless cores may be oscillating perturbations on a thermally supported equilibrium structure. Such oscillations can produce molecular line maps which mimic rotation, collapse or expansion, and thus could make determining the dynamical state from such observations alone difficult. However, while B68 is embedded in a very hot, low-density medium, many starless cores are not, having interior/exterior density contrasts closer to unity. In this paper we investigate the oscillation damping rate as a function of the exterior density. For concreteness we use the same interior model employed in Broderick et al. (2007), with varying models for the exterior gas. We also develop a simple analytical formalism, based upon the linear perturbation analysis of the oscillations, which predicts the contribution to the damping rates due to the excitation of sound waves in the external medium. We find that the damping rate of oscillations on globules in dense molecular environments is always many periods, corresponding to hundreds of thousands of years, and persisting over the inferred lifetimes of the globules.