Gravitational Collapse of Interstellar Magnetized Clouds

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The evolution of an isothermal magnetized interstellar cloud was studied with a parallelized magnetohydrodynamics (MHD) code and a fast Poisson solver based on the CGS (conjugate gradient squared) method.Since the density distribution of a cloud in the dynamical contraction phase is central-peaked, the code must have fine spatial resolution near the center, while in the outer part numerical grid must be large. The 'nested grid technique' meets these contradictory conditions. A number of grids are prepared ; finer ones cover only the central part, while coarser ones cover the whole cloud.1.From the numerical simulation using the nested grid method, it is shown that (1) a disk is formed perpendicular to the magnetic field lines, and that (2) the disk evolves in a self-similar manner and the solution reaches a special power-law distribution : for example, the density on the equatorial plane indicates a power-law as p (r) * r^<-2>.2.In a finite time, the solution becomes singular. After the epoch, matter begins to accrete onto a central body with a finite mass. This is studied using a sink cell method. (1) From this, it is shown that an outward-facing shock front is formed in the disk in the accretion phase. Infalling matter is stopped at the shock surface and is accelerated again. (2) The mass accretion rate is much larger than the standard rate obtained by Shu.