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Conditions for Justifying Single-fluid Approximation for Charged and Neutral Dust Fluids and a Smoothed Particle Magnetohydrodynamics Method for Dust–Gas Mixture
The Astrophysical Journal ( IF 4.9 ) Pub Date : 2021-06-07 , DOI: 10.3847/1538-4357/abf5db
Y. Tsukamoto 1 , M. N. Machida 2 , S. Inutsuka 3
Affiliation  

We describe a numerical scheme for magnetohydrodynamics simulations of dust–gas mixture by extending smoothed particle magnetohydrodynamics. We employ the single-species particle approach to describe dust–gas mixture with several modifications from the previous studies. We assume that the charged and neutral dust can be treated as single-fluid, that the electromagnetic force acts on the gas, and that that acting on the charged dust is negligible. The validity of these assumptions in the context of protostar formation is not obvious and is extensively evaluated. By investigating the electromagnetic force and electric current with terminal velocity approximation, it is found that as the dust size increases, the contribution of dust to them becomes smaller and negligible. We conclude that our assumption that the electromagnetic force on the dusts is negligible is valid for the dust size with a d ≳ 10 μm. On the other hand, they do not produce the numerical artifact for the dust a d ≲ 10 μm in the envelope and disk, where the perfect coupling between gas and dust is realized. However, we also found that our assumptions may break down in outflow (or under an environment with very strong magnetic field and low density) for the dust a d ≲ 10 μm. We conclude that our assumptions are valid in almost all cases where macroscopic dust dynamics is important in the context of protostar formation. We conduct numerical tests of dusty waves, dusty magnetohydrodynamics shocks, and gravitational collapse of magnetized cloud cores with our simulation code. The results show that our numerical scheme well reproduces the dust dynamics in the magnetized medium.



中文翻译:

证明带电和中性粉尘流体的单流体近似以及粉尘-气体混合物的平滑粒子磁流体动力学方法合理的条件

我们通过扩展平滑粒子磁流体动力学来描述粉尘-气体混合物的磁流体动力学模拟的数值方案。我们采用单物种粒子方法来描述粉尘 - 气体混合物,并对之前的研究进行了一些修改。我们假设带电尘埃和中性尘埃可以看作单一流体,电磁力作用在气体上,作用在带电尘埃上的电磁力可以忽略不计。在原恒星形成的背景下,这些假设的有效性并不明显,并且得到了广泛的评估。通过研究终端速度近似的电磁力和电流,发现随着灰尘尺寸的增加,灰尘对它们的贡献变得越来越小,可以忽略不计。a d ≳ 10 μ m。另一方面,它们不会产生包络和圆盘中尘埃a d ≲ 10 μ m的数值伪影,实现了气体和尘埃之间的完美耦合。然而,我们也发现我们的假设可能在流出时(或在磁场非常强且密度低的环境下)失效,对于a d ≲ 10 μ 米。我们得出的结论是,我们的假设几乎适用于宏观尘埃动力学在原恒星形成背景下很重要的所有情况。我们使用我们的模拟代码对尘埃波、尘埃磁流体动力学冲击和磁化云核的引力坍缩进行数值测试。结果表明,我们的数值方案很好地再现了磁化介质中的尘埃动力学。

更新日期:2021-06-07
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