arXiv 2009.077962020-09-16astro-ph.SRastro-ph.EPastro-ph.HE

原恒星盘形成和演化中的霍尔效应

Hall Effect in Protostellar Disc Formation and Evolution

Bo Zhao, Paola Caselli, Zhi-Yun Li, Ruben Krasnopolsky, Hsien Shang, Ka Ho Lam

备注：: 22 pages, 18 figures
发表信息：: MNRAS 492, 3375Z (2020)
DOI：: 10.1093/mnras/staa041

摘要：

最近的霍尔效应被证明是有效的磁化致密的分子核心，并可能导致双峰形成的旋转支撑盘（RSD）的第一个核心阶段。然而，这种霍尔主导的系统如何在原恒星吸积阶段演化仍然不清楚。我们进行了二维轴对称模拟，包括霍尔效应和欧姆耗散，与现实的磁扩散率计算从我们的平衡化学网络。我们发现，霍尔效应只有在从标准MRN尺寸分布中去除大量非常小的晶粒（VSG：$\lesssim$ 10 nm）时才变得有效。然而，由于这种增强的霍尔效应，盘形成的双峰性不会继续进入主吸积阶段。当霍尔效应使极向磁场相对于物质径向向内移动时，以反对准配置（${\bf Ω\cdot B}<0$）形成的初始$\sim$ 40 AU盘的外部部分变成薄的旋转支撑霍尔电流片，仅留下内部$\lesssim$ 10- 20 AU RSD。在对齐配置（${\bf Ω\cdot B}>0$），光盘的形成最初被抑制，但反向旋转的光盘形成随后由于有效的方位角霍尔漂移。随着霍尔效应径向向外移动磁场，反向旋转盘首先增长到$\sim$ 30 AU，但只有内部$\lesssim$ 10 AU RSD像反对齐情况一样是长寿命的。除了去除VSG，宇宙射线电离率应低于几个10 $^{-16}$ s $^{-1}$的霍尔效应是有效的磁盘形成。我们的结论是，霍尔效应产生小$\lesssim$ 10- 20 AU光盘，无论磁场的极性，径向向外扩散的磁场仍然是至关重要的光盘的形成和增长。

英文摘要：

The Hall effect is recently shown to be efficient in magnetized dense molecular cores, and could lead to a bimodal formation of rotationally supported discs (RSDs) in the first core phase. However, how such Hall dominated systems evolve in the protostellar accretion phase remains unclear. We carry out 2D axisymmetric simulations including Hall effect and Ohmic dissipation, with realistic magnetic diffusivities computed from our equilibrium chemical network. We find that Hall effect only becomes efficient when the large population of very small grains (VSGs: $\lesssim$10 nm) is removed from the standard MRN size distribution. With such an enhanced Hall effect, however, the bimodality of disc formation does not continue into the main accretion phase. The outer part of the initial $\sim$40 AU disc formed in the anti-aligned configuration (${\bf Ω\cdot B}<0$) flattens into a thin rotationally supported Hall current sheet as Hall effect moves the poloidal magnetic field radially inward relative to matter, leaving only the inner $\lesssim$10--20 AU RSD. In the aligned configuration (${\bf Ω\cdot B}>0$), disc formation is suppressed initially but a counter-rotating disc forms subsequently due to efficient azimuthal Hall drift. The counter-rotating disc first grows to $\sim$30 AU as Hall effect moves the magnetic field radially outward, but only the inner $\lesssim$10 AU RSD is long-lived like in the anti-aligned case. Besides removing VSGs, cosmic ray ionization rate should be below a few 10$^{-16}$ s$^{-1}$ for Hall effect to be efficient in disc formation. We conclude that Hall effect produces small $\lesssim$10--20 AU discs regardless of the polarity of the magnetic field, and that radially outward diffusion of magnetic fields remains crucial for disc formation and growth.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

摘要：

英文摘要：

相关论文