Oscillations of Starless Cores

Abstract

If the split, asymmetric molecular spectral line profiles that are seen in many starless cores are interpreted as indicative of global collapse or expansion of the core, then one possible implication is that most starless cores have short lifetimes, on the order of the collapse or sound crossing timescale. An alternative interpretation of the line profiles, as indicative of perturbations on an underlying equilibrium structure, leads to the opposite implication, that many cores have long lifetimes. While evidence suggests that some cores are collapsing on a free-fall timescale, we show that observations of some other starless cores can be reproduced by a model of nonradial oscillations about the equilibrium configuration of a pressure-bounded, thermally-supported sphere (Bonnor-Ebert sphere). We model the oscillations as linear perturbations following a standard analysis developed for stellar pulsations and compare the column densities and molecular spectral line profiles predicted from a particular model to observations of the Bok globule B68.