Gravitational Collapse of Interstellar Magnetized Clouds

采用并行磁流体力学（MHD）程序和基于共轭梯度平方法（CGS）的快速泊松求解器研究了等温磁化星际云的演化。由于云在动力收缩阶段的密度分布是中心峰的，因此代码在中心附近必须具有良好的空间分辨率，而在外围部分则必须有较大的数值网格。“嵌套网格技术”满足了这些矛盾的条件。准备了一些网格；较细的云只覆盖了中心部分，而较粗的云覆盖了整个云。利用嵌套网格法的数值模拟表明：(1)垂直于磁力线形成一个圆盘；(2)圆盘以自相似的方式演化，解达到一个特殊的幂律分布：如赤道面上的密度表示幂律为p (r) * r^<-2>.2。在有限时间内，解变得奇异。在这一时期之后，物质开始吸积到一个质量有限的中心物体上。这是用汇池法研究的。(1)由此可见，在吸积阶段，盘内形成了一个向外的激波前缘。下落的物质在激波表面停止并再次加速。(2)质量吸积速率远大于Shu得到的标准速率。

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.