Collapse-Driven Outflow in Star-Forming Molecular Cores

Dynamical collapses of magnetized molecular cloud cores are studied with magnetohydrodynamic simulations from the runaway collapse phase to the accretion phase. In the runaway collapse phase, a disk threaded by magnetic field lines is contracting owing to its self-gravity, and its evolution is well expressed by a self-similar solution. The central density increases greatly in a finite timescale and reaches a density at which an opaque core is formed at the center. After that, matter accretes to the newly formed core (accretion phase). In this stage, a rotationally supported disk is formed in a cloud core without magnetic fields. In contrast, the disk continues to contract in the magnetized cloud core, since the magnetic fields transfer angular momentum from the disk. Its rotation motion winds up the threading magnetic field lines. Eventually, strong toroidal magnetic fields are formed and begin to drive the outflow, even if there is no toroidal field component initially. Bipolar molecular outflows observed in protostar candidates are naturally explained by this model.

[1]  D. C. Black,et al.  Numerical calculations of the collapse of nonrotating, magnetic gas clouds , 1980 .

[2]  P. Foster,et al.  Gravitational collapse of an isothermal sphere , 1992 .

[3]  F. Shu.  Self-similar collapse of isothermal spheres and star formation. , 1977 .

[4]  F. Nakamura,et al.  Fragmentation of Filamentary Molecular Clouds with Longitudinal Magnetic Fields: Formation of Disks and Their Collapse , 1995 .

[5]  R. Bachiller.  BIPOLAR MOLECULAR OUTFLOWS FROM YOUNG STARS AND PROTOSTARS , 1996 .

[6]  Colin Norman,et al.  Bipolar hydromagnetic winds from disks around protostellar objects , 1986 .

[7]  Kohji Tomisaka.  Collapse and Fragmentation of Cylindrical Magnetized Clouds: Simulation with Nested Grid Scheme , 1996 .

[8]  R. Blandford,et al.  Hydromagnetic flows from accretion discs and the production of radio jets , 1982 .

[9]  R. Pudritz,et al.  Numerical Simulations of Astrophysical Jets from Keplerian Disks. II. Episodic Outflows , 1997 .

[10]  F. Shu,et al.  Collapse of Magnetized Molecular Cloud Cores. II. Numerical Results , 1993 .

[11]  S. Basu.  A Semianalytic Model for Supercritical Core Collapse: Self-Similar Evolution and the Approach to Protostar Formation , 1997 .

[12]  Accretion in Gravitationally Contracting Clouds , 1996, astro-ph/9610001.

[13]  F. Nakamura,et al.  Gravitational Contraction of Rotating Clouds: Formation of Self-similarly Collapsing Disks , 1997 .

[14]  Hirohiko Masunaga,et al.  A Radiation Hydrodynamic Model for Protostellar Collapse. I. The First Collapse , 1998 .

[15]  C. Hunter.  The collapse of unstable isothermal spheres. , 1977 .

[16]  S. Miyama,et al.  Characteristics of Collapse of Rotating Isothermal Clouds , 1984 .

[17]  A. Whitworth,et al.  Self-similar condensation of spherically symmetric self-gravitating isothermal gas clouds , 1985 .

[18]  F. Nakamura,et al.  Nonaxisymmetric Evolution of Dynamically Contracting Disks and Its Implication for Binary Formation , 1997 .

[19]  Collapse and Fragmentation of Magnetized Cylindrical Clouds , 1993, astro-ph/9306028.

[20]  M. Penston.  Dynamics of Self-Gravitating Gaseous Spheres—III: Analytical Results in the Free-fall of Isothermal Cases , 1969 .

[21]  Richard B. Larson,et al.  Numerical Calculations of the Dynamics of a Collapsing Proto-Star , 1969 .

[22]  K. Saigo,et al.  Similarity Solution for Formation of a Circumstellar Disk through the Collapse of a Flattened Rotating Cloud , 1998 .

[23]  M. L. Norman,et al.  A new calculation on rotating protostar collapse , 1980 .