2003/11/17 by A. Allen, Z. Y. Li, Zhi‐Yun Li +2 · 291 citations
Physics and Astronomy · #Accretion (finance) #Angular momentum #Angular velocity #Astro and Planetary Science #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Atomic and Molecular Physics #Classical mechanics #Flattening #Geometry #Magnetic field #Magnetohydrodynamics #Mechanics #Physics #Protostar #Quantum mechanics #Rotation (mathematics) #Rotational speed #Star formation #Toroid #astro-ph
paper · pdf · doi:10.1086/379243
published in The Astrophysical Journal 599(1), 363-379 (IOP Publishing) · 38 pages, 9 figures. To appear in v599 n1 ApJ December 10, 2003 issue
arxiv created 2003/11/17 · openalex publication_date 2003/12/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We study numerically the collapse of rotating magnetized molecular cloud cores, focusing on rotation and magnetic braking during the main accretion phase of isolated star formation. Motivated by previous numerical work and analytic considerations, we idealize the precollapse core as a magnetized singular isothermal toroid, with a constant rotational speed everywhere. The collapse starts from the center and propagates outward in an inside-out fashion, satisfying exact self-similarity in space and time. For rotation rates and field strengths typical of dense low-mass cores, the main feature remains the flattening of the mass distribution along field lines—the formation of a pseudodisk, as in the nonrotating cases. The density distribution of the pseudodisk is little affected by rotation. On the other hand, the rotation rate is strongly modified by pseudodisk formation. Most of the centrally accreted material reaches the vicinity of the protostar through the pseudodisk. The specific angular momentum can be greatly reduced on the way, by an order of magnitude or more, even when the precollapse field strength is substantially below the critical value for dominant cloud support. The efficient magnetic braking is due to the pinched geometry of the magnetic field in the pseudodisk, which strengthens the magnetic field and lengthens the level arm for braking. Both effects enhance the magnetic transport of angular momentum from inside to outside. The excess angular momentum is carried away in a low-speed outflow that has, despite claims made by other workers, little in common with observed bipolar molecular outflows. We discuss the implications of our calculations for the formation of true disks that are supported against gravity by rotation.