Study of Cosmic Electromagnetic Phenomena by using 3-D MHD Code

开发了3D MHD程序，研究了旋转、磁化等温云在不同条件下的平衡结构，并考虑了磁场和双极扩散引起的角动量损失对其演化的影响。在这项研究中，我用MHD程序研究了同时考虑自转和磁场的等温云的平衡。此外，还跟踪了它们的演变。固定质量云有两种平衡解：一种是稳定的，另一种是不稳定的。当云团有一个临界质量时，这两个解是一致的，在这个临界质量以上，对于给定的磁场和角动量分布，没有平衡解。这一临界质量与磁场强度和总角动量的关系已经明确，我们得到了一个简单的代数方程。利用这个方程，我们可以很容易地看到云的稳定性和观察到的云的磁场强度。结果表明，旋转的磁化云的演化相当简单。在内区，考虑角动量损失时，磁压占主导地位，而在外区，离心力占主导地位。这导致内部区域在保持外部旋转的圆盘不变的情况下塌缩为恒星。这种演化行为敏感地依赖于双极扩散引起的磁场损失率和相关的角动量损失。目前，这些物理本质的细节都是通过一个简单的模型来探索的，云的稳定性和星际磁场的构型是强耦合的，它们的耦合会影响云的形成和平衡图形。这是一个需要进一步研究的重要问题。

Developing the 3D MHD code, I have investigated the equilibrium structures of rotating, magnetized isothermal clouds under various conditions, and also have examined their evolution in consideration of magnetic field and angular momentum loss due to the ambipolar diffusion.Till the present work, the equilibrium structures of rotating clouds without magnetic field or those of magnetized clouds without rotation have been studied. In this research, I have explored the equilibria of isothermal clouds considering both the rotation and magnetic field by using the MHD code. Further, the evolution of them has been followed. There are two kinds of equilibrium solutions for a fixed mass cloud: one is stable and the other is unstable. These two solutions coincide when the cloud has a critical mass, above which there are no equilibrium solutions for a given magnetic field and angular momentum distribution. The dependence of this critical mass upon magnetic field strength and total angular momentum has been made clear, and we have got a simple algebraic equation for it.Utilizing this equation, we can easily see the stability of clouds and magnetic field strength for o bserved clouds.It is shown that the evolution of rotating, magnetized clouds is rather simple. At the innner region, the magnetic pressure dominates when the angular momentum loss is included and at the outer region the centrifugal force dom-inates. This results in the collapse of inner region to stars with keeping the outer, rotating disk. This evolutionary behavior sensitively depends upon the loss rate of magnetic field due to ambipolar diffusion and associated angular momentum loss. At present, the details of these physical essence are explored by means of a simple model.The stability of clouds and configuration of interstellar magnetic field are strongly coupled, and their coupling will affect the formation and equilibrium figures of clouds. This is an important problem to be examined more.