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.

角动量的调节在恒星形成过程中至关重要，因为它直接影响行星的形成，以及原行星盘可能的碎片导致双星的产生。磁场通过减慢气体的旋转在此过程中发挥着重要作用。这种“制动”的效率取决于磁场和气体之间的耦合，而这又与化学环境有关。三种效应会影响联轴器，从而影响制动。它们是“非理想磁流体动力学（MHD）效应”，即欧姆扩散、霍尔效应和双极扩散。磁场还可以发射原恒星外流，从而消除原恒星系统的质量和角动量。在他的研究金的第二年，马尔尚博士使用欧拉代码 RAMSES 进行了恒星形成的数值模拟，其中包括自重力和双极扩散。他研究了不同化学环境和不同初始条件下双极扩散对磁制动的影响。他确定，在每种情况下，磁制动从磁盘上消除的角动量都比流出的角动量多，这仍然是一个有争议的问题。他发现，减少小尘埃颗粒的数量会导致圆盘稍大一些，但磁制动和原恒星外流会明显减弱。在这种情况下，他还发现了原恒星流出的离子前体，这是以前从未报道过的现象。