On the Internal Dynamics of the Starless Core L694-2

On the Internal Dynamics of Starless Cores: Stability of Starless Cores With Internal Motions and Collapse Dynamics

“…Their studies show that 25%, 27%, and 20% of their samples, respectively, have blue-skewed line profiles indicative of infall. In addition, studies on the internal velocity fields of L694-2 and L1197 with radiative transfer models and dynamical simulations (Lee et al 2007;Seo et al 2011b) suggest that both starless cores have supersonic infall motions substantially faster and occurring in a narrower layer than predicted by quasi-static gravitational collapse. Such fast infall motions may appear in a scenario of colliding shocks where the turbulent surrounding may enhance infall speed in a narrow layer (Gómez et al 2007) and considerably affect stability of the starless cores because the ram pressure P ram ∼ ρv 2 becomes comparable to the surface pressure P surf ∼ ρc 2 s .…”

“…Dynamical evolution of starless cores in the limit of negligible external dynamics (gravity dominant limit) are relatively well studied utilizing similarity solutions and numerical simulations (e.g. Larson 1969;Penston 1969;Shu 1977;Hunter 1977;Foster & Chevalier 1993;Aikawa et al 2005;Seo et al 2011b). The fiducial model in this limit is the collapse of a self-gravitating, isothermal, hydrostatic gas sphere bound by external pressure called the Bonnor-Ebert sphere (Ebert 1955;Bonnor 1956;Ebert 1957;hereafter BE).…”

“…This model has been widely used because it is a physically well established model with its column density profile similar to observed column densities in near-IR absorptions and dust continuum emissions (e.g., Alves et al 2001;Evans et al 2001;Tafalla et al 2002;Harvey et al 2003aHarvey et al , 2003bKandori et al 2005). In this model, the critical BE sphere collapses while maintaining a BE-like density profile (Foster & Chevalier 1993;Aikawa et al 2005;Seo et al 2011b). However, the initial BE sphere is a hydrostatic sphere neglecting any internal motion, whereas real starless cores are likely contracting, expanding, or oscillating (e.g.…”

“…Without any initial internal motion and external perturbation, the dynamics of the starless core depend only on the density distribution and there are two limits of the density distributions for starless cores: the BE sphere and a uniform sphere. The collapse of the critical BE sphere gives the slowest infall with respect to the density concentration (Seo et al 2011b) and provides the lower limit of the infall speed in spontaneous gravitational collapse (or pure gravitational collapse). A starless core that collapses slower than this model is likely to be perturbed by external perturbations or is not isothermal.…”

“…The uniform sphere is a starless core with the least pressure gradient against the self-gravity for its initial conditions. Inevitably, the sphere develops a faster infall motion than the collapse of the critical BE sphere at a given density structure (Seo et al 2011b). Since the uniform density field has the shallowest profile that a starless core can have, the collapse of the critical uniform sphere has the fastest infall speed with respect to a given density concentration (in the absence of external perturbations).…”