Oscillating Starless Cores: the Nonlinear Regime

In a previous paper, we modeled the oscillations of a thermally-supported (Bonnor-Ebert) sphere as non-radial, linear perturbations following a standard analysis developed for stellar pulsations. 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. However, the linear analysis is unable to address several questions, among them the stability, and lifetime of the perturbations. In this paper we simulate the oscillations using a three-dimensional numerical hydrodynamic code. We find that the oscillations are damped predominantly by non-linear mode-coupling, and the damping time scale is typically many oscillation periods, corresponding to a few million years, and persisting over the inferred lifetime of gobules. Subject headings: stars: formation, hydrodynamics, radiation mechanisms: non-thermal, line: profiles, ISM: globules, ISM: clouds