1999/11/10 by Kohji Tomisaka · 2 citations
Physics and Astronomy · #Accretion (finance) #Angular momentum #Angular momentum coupling #Angular momentum of light #Astro and Planetary Science #Astrophysics #Astrophysics and Star Formation Studies #Classical mechanics #Magnetic field #Magnetohydrodynamics #Mechanics #Outflow #Physics #Quantum mechanics #Rotational symmetry #Specific relative angular momentum #Stellar, planetary, and galactic studies #Total angular momentum quantum number #astro-ph
paper · pdf · doi:10.1086/312417
15 pages, 2 figures, Astrophysical Journal Letters in press
arxiv created 1999/11/10 · openalex publication_date 2000/01/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
If the angular momentum of the molecular cloud core were conserved during the star formation process, a newborn star would rotate much faster than its fission speed. This constitutes the angular momentum problem of newborn stars. In this Letter, the angular momentum transfer in the contraction of a rotating magnetized cloud is studied with axisymmetric MHD simulations. Because of the large dynamic range covered by the nested-grid method, the structure of the cloud in the range from 10 AU to 0.1 pc is explored. First, the cloud experiences a runaway collapse, and a disk forms perpendicularly to the magnetic field, in which the central density increases greatly in a finite timescale. In this phase, the specific angular momentum j of the disk decreases to about one-third of the initial cloud. After the central density of the disk exceeds approximately 1010 cm-3, the infall on to the central object develops. In this accretion stage, the rotation motion and thus the toroidal magnetic field drive the outflow. The angular momentum of the central object is transferred efficiently by the outflow as well as by the effect of the magnetic stress. In 7000 yr from the core formation, the specific angular momentum of the central 0.17 M middle dot in circle decreases a factor of 10-4 from the initial value (i.e., from 1020 to 1016 cm2 s-1).