Impact of the Hall effect in star formation and the issue of angular momentum conservation
Impact of the Hall effect in star formation and the issue of angular momentum conservation
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霍尔效应对恒星形成的影响和角动量守恒问题
DOI：
10.1051/0004-6361/201832907
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发表时间：
2018
影响因子：
6.5
通讯作者：
G.
中科院分区：
文献类型：
--
作者：
Marchand;P.; Commercon;B.; Chabrier;G.
我们将非理想磁流体方程中的霍尔项应用到自适应网格精化程序Ramses中，以研究它对恒星形成的影响。最近的工作表明，霍尔效应对致密磁芯崩塌、加强或削弱磁制动时角动量的调节有很大影响。我们的方法包括对二维约束输运方案的修改。我们的格式在空间上表现出二阶收敛，并且哨声波的传播频率是精确的。我们证实了以前的结果，即在崩塌过程中，霍尔效应产生了流体在中面上的旋转，其方向取决于霍尔电阻率的符号，而在中面的两边都形成了反旋转的包络。然而，我们发现我们的数值结果的可预测性是严重有限的。在我们用霍尔效应进行的致密核坍塌模拟中，角动量并不守恒：在第一个拉尔森核形成几百年后，在其内部产生了大量的角动量，而没有得到周围气体的补偿。这个问题在以前的研究中没有提到，可能与拉森核上吸积激波的形成有关。我们预计，这种数值效应在恒星形成模拟中可能是一个严重的问题。
We present an implementation of the Hall term in the non-ideal magnetohydrodynamics equations into the adaptive-mesh-refinement code RAMSES to study its impact on star formation. Recent works show that the Hall effect heavily influences the regulation of the angular momentum in collapsing dense cores, strengthening or weakening the magnetic braking. Our method consists of a modification of the two-dimensional constrained transport scheme. Our scheme shows convergence of second order in space and the frequency of the propagation of whistler waves is accurate. We confirm previous results, namely that during the collapse, the Hall effect generates a rotation of the fluid with a direction in the mid-plane that depends on the sign of the Hall resistivity, while counter-rotating envelopes develop on each side of the mid-plane. However, we find that the predictability of our numerical results is severely limited. The angular momentum is not conserved in any of our dense core-collapse simulations with the Hall effect: a large amount of angular momentum is generated within the first Larson core, a few hundred years after its formation, without compensation by the surrounding gas. This issue is not mentioned in previous studies and may be correlated to the formation of the accretion shock on the Larson core. We expect that this numerical effect could be a serious issue in star formation simulations.