磁场在恒星形成中的作用
The role of magnetic fields in star formation
摘要：
恒星的形成被认为是由分子云致密核心的引力坍缩引发的。坍塌过程中的角动量守恒导致离心力的逐渐增加，最终阻止材料的流入，并导致由圆盘包围的中心质量的发展。在角动量传输机制存在的情况下，质量吸积到中心物体上的过程通过这个圆盘进行，人们认为这是恒星通常获得大部分质量的方式。然而，负责这种角动量传输的机制还没有得到很好的理解。最有希望的是由磁旋转不稳定性（MRI）驱动的湍流粘性，以及从圆盘表面离心加速的流出。这两个过程都是由磁场的作用提供动力的，反过来，可能会强烈影响其宿主圆盘的结构，动力学，进化路径和行星形成能力。然而，原恒星盘的弱电离可能会阻止磁场有效地耦合到气体并驱动这些过程。在这里，我研究的可行性和这些磁驱动过程中的原恒星盘的属性。结果表明，尽管弱电离，该领域是能够耦合到气体和剪切流体的条件被认为是满足在这些光盘的半径范围很广。
英文摘要：
Star formation is thought to be triggered by the gravitational collapse of the dense cores of molecular clouds. Angular momentum conservation during the collapse results in the progressive increase of the centrifugal force, which eventually halts the inflow of material and leads to the development of a central mass surrounded by a disc. In the presence of an angular momentum transport mechanism, mass accretion onto the central object proceeds through this disc, and it is believed that this is how stars typically gain most of their mass. However, the mechanisms responsible for this transport of angular momentum are not well understood. The most promising are turbulence viscosity driven by the magnetorotational instability (MRI), and outflows accelerated centrifugally from the surfaces of the disc. Both processes are powered by the action of magnetic fields and are, in turn, likely to strongly affect the structure, dynamics, evolutionary path and planet-forming capabilities of their host discs. The weak ionization of protostellar discs, however, may prevent the magnetic field from effectively coupling to the gas and drive these processes. Here I examine the viability and properties of these magnetically driven processes in protostellar discs. The results indicate that, despite the weak ionization, the field is able to couple to the gas and shear for fluid conditions thought to be satisfied over a wide range of radii in these discs.
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