The regulation of angular momentum in star formation: the secret behind planet formation

恒星形成过程中角动量的调节：行星形成背后的秘密

基本信息

批准号：
17F17802
负责人：
長峯健太郎
金额：
$ 1.47万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for JSPS Fellows
财政年份：
2017
资助国家：
日本
起止时间：
2017-11-10 至 2020-03-31
项目状态：
已结题

项目摘要

The regulation of angular momentum is of prime importance during star formation, as it directly impacts the formation of planets, and the possible fragmentation of the protoplanetary disk leading to the creation of binary stars. The magnetic field plays a major role in this process by slowing down the rotation of the gas. The efficiency of this "braking" depends on the coupling between the magnetic field and the gas, which is related to the chemical environment. Three effects impact the coupling, and therefore the braking. They are "non-ideal magnetohydrodynamics (MHD) effects", namely the Ohmic diffusion, the Hall effect and the ambipolar diffusion. The magnetic field can also launch protostellar outflows, that remove mass and angular momentum from the proto-stellar system.During the second year of his fellowship, Dr. Marchand have performed numerical simulations of star formation using the eulerian code RAMSES, that includes self-gravity and the ambipolar diffusion. He has studied how the magnetic braking was impacted by the ambipolar diffusion in different chemical environments and with different initial conditions. He determined that in every situation, the magnetic braking removes more angular momentum from the disk than the outflows, which is still a debated question. He found that reducing the number of small dust grains leads to a moderately larger disk, but significantly weaker magnetic braking and protostellar outflows. In this situation, he also found an ionic precursor to the protostellar outflow, a phenomenon never reported before.

在恒星形成过程中，角动量的调节至关重要，因为它直接影响行星的形成，以及可能导致二进制恒星创建的原星盘的碎片。磁场在此过程中通过减慢气体的旋转而起着重要作用。该“制动”的效率取决于与化学环境有关的磁场和气体之间的耦合。三个影响影响耦合，因此影响刹车。它们是“非理想的磁流失动力学（MHD）效应”，即欧姆扩散，霍尔效应和双相扩散。磁场还可以发射ProtoStellar流出，从而消除了原始系统系统中的质量和角动量。在他的团契第二年，Marchand博士使用Eulerian Code Ramses进行了恒星形成的数值模拟，其中包括自我graveity和Ambipolar的扩散。他研究了在不同的化学环境和不同初始条件下，磁制动如何受到双极扩散的影响。他确定，在每种情况下，磁制动都比流出相比，从磁盘上消除了更多的角度动量，这仍然是一个有争议的问题。他发现，减少小尘土的数量会导致中等较大的磁盘，但明显弱的磁制动和原恒星流出。在这种情况下，他还发现了原始流出的离子前体，这种现象从未报道过。