2008/04/27 by Takahiro Kudoh, Shantanu Basu · 54 citations
Physics and Astronomy · #Ambipolar diffusion #Astro and Planetary Science #Astrophysics #Astrophysics and Star Formation Studies #Classical mechanics #Computational physics #Magnetic field #Magnetohydrodynamics #Mechanics #Nonlinear system #Nuclear physics #Physics #Plasma #Stellar, planetary, and galactic studies #Supersonic speed #Turbulence #astro-ph
paper · pdf · doi:10.1086/589618
published in The Astrophysical Journal 679(2), L97-L100 (IOP Publishing) · 12 pages, 4 figures, accepted for publication in ApJL, a preprint and a movie at http://yso.mtk.nao.ac.jp/~kudoh/publist_e.html
arxiv created 2008/04/27 · openalex publication_date 2008/05/02 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We demonstrate that the formation of collapsing cores in subcritical clouds is accelerated by nonlinear flows, by performing three-dimensional nonideal MHD simulations. An initial random supersonic (and trans-Alfvénic) turbulent-like flow is input into a self-gravitating gas layer that is threaded by a uniform magnetic field (perpendicular to the layer) such that the initial mass-to-flux ratio is subcritical. Magnetic ambipolar diffusion occurs very rapidly initially due to the sharp gradients introduced by the turbulent flow. It subsequently occurs more slowly in the traditional near-quasi-static manner, but in regions of greater mean density than present in the initial state. The overall timescale for runaway growth of the first core(s) is several × 10 6 yr, even though previous studies have found a timescale of several × 10 7 yr when starting with linear perturbations and similar physical parameters. Large-scale supersonic flows exist in the cloud and provide an observationally testable distinguishing characteristic from core formation due to linear initial perturbations. However, the nonlinear flows have decayed sufficiently that the relative infall motions onto the first core are subsonic, as in the case of starting from linear initial perturbations. The ion infall motions are very similar to those of neutrals; however, they lag the neutral infall in directions perpendicular to the mean magnetic field direction and lead the neutral infall in the direction parallel to the mean magnetic field.