Simulations of the Isothermal Collapse of Magnetic Rotating Protostellar Clouds

Abstract

We investigate the collapse of magnetic protostellar clouds of mass 10 and $1\;{{M}_{ \odot }}$. The collapse is simulated numerically using the two-dimensional magneto-gas-dynamic (MHD) code “Enlil.” The simulations show that protostellar clouds acquire a hierarchical structure by the end of the isothermal stage of collapse. Under the action of the electromagnetic force, the protostellar cloud takes the form of an oblate envelope with the half-thickness to radius ratio $Z{\text{/}}R \sim 0.20{-} 0.95$. A geometrically and optically thin primary disk with radius $(0.2{-} 0.7){{R}_{0}}$ and $Z{\text{/}}R$ ~ (10^–2–10^–1) forms inside the envelope, where ${{R}_{0}}$ is the initial radius of the cloud. Primary disks are the structures in magnetostatic equilibrium. They form when the initial magnetic energy of the cloud exceeds 20% of its gravitational energy. The mass of the primary disk is 30–80% of the initial mass of the cloud. The first hydrostatic core subsequently forms in the center of the primary disc. We discuss the role of primary disks in the further evolution of clouds, as well as possible observational appearance of the internal hierarchy of the collapsing cloud from the point of view of the features of the magnetic field geometry and the distribution of angular momentum at different levels of the hierarchy.