Collapse of Rotating Magnetized Molecular Cloud Cores and Mass Outflows

Collapse of the rotating magnetized molecular cloud core is studied with theaxisymmetric magnetohydrodynamical (MHD) simulations. Due to the change of theequation of state of the interstellar gas, the molecular cloud cores experienceseveral different phases as collapse proce eds. In the isothermal run-awaycollapse ($n \lesssim 10^{10}{\rm H_2 cm}^{-3}$), a pseudo-disk is formed andit continues to contract till the opaque core is fo rmed at the center. In thisdisk, a number of MHD fast and slow shock pairs appear running parallelly tothe disk. After the equation of state becomes hard, an adiabatic core isformed, which is separated from the isothermal contracting pseudo-disk by theaccretion shock front facing radially outwards. By the effect of the magnetictension, the angular momentum is transferred from the disk mid-plane to thesurface. The gas with excess angular momentum near the surface is finallyejected, which explains the molecular bipolar outflow. Two types of outflowsare observed. When the poloidal magnetic field is strong (magnetic energy iscomparable to the thermal one), a U-shaped outflow is formed in which fastmoving gas is confined to the wall whose shape looks like a capit al letter U.The other is the turbulent outflow in which magnetic field lines and velocityfi elds are randomly oriented. In this case, turbulent gas moves out almostperpendicularly from the disk. The continuous mass accretion leads to thequasistatic contraction of the first core. A second collapse due todissociation of H$_2$ in the first core follows. Finally another quasistaticcore is again formed by atomic hydrogen (the second core). It is found thatanother outflow is ejected around the second atomic core, which seems tocorrespond to the optical jets or the fast neutral winds.Comment: submitted to Ap