Saturation of the magnetorotational instability and the origin of magnetically elevated accretion discs
Mitchell C. Begelman, Philip J. Armitage
备注：
9 pages, 2 figures, to be published in Monthly Notices of the Royal Astronomical Society. Replaces arXiv:2211.09261, eliminating section 2.2 and with moderate revisions and clarifications in sections 3.1, 3.3, 4.2 and 4.3
We propose that the strength of angular momentum transport in accretion discs threaded by net vertical magnetic field is determined by a self-regulation mechanism: the magnetorotational instability (MRI) grows until its own turbulent resistivity damps the fastest growing mode on the scale of the disc thickness. Given weak assumptions as to the structure of MRI-derived turbulence, supported by prior simulation evidence, the proposed mechanism reproduces the known scaling of the viscous $α$-parameter, $α\propto β_z^{-1/2}$. Here, $β_z = 8πp_g/B_{z0}^2$ is the initial plasma $β$-parameter on the disc midplane, $B_{z0}$ is the net field, and $p_g $ is the midplane gas pressure. We generalize the argument to discs with strong suprathermal toroidal magnetic fields, where the MRI growth rate is modified from the weak-field limit. Additional sources of turbulence are required if such discs are to become magnetically elevated, with the increased scale heights near the midplane that are seen in simulations. We speculate that tearing modes, associated with current sheets broadened by the effective resistivity, are a possible source of enhanced turbulence in elevated discs.
Matter- and magnetically-driven flavor conversion of neutrinos in magnetorotational collapses
Università del Salento（萨莱诺大学）；INFN-Istituto Nazionale di Fisica Nucleare, Sezione di Lecce（意大利国家核物理研究所莱切分部）；Niels Bohr International Academy and DARK, Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯·玻尔学院及DARK中心）
Radiation GRMHD Models of Accretion onto Stellar-Mass Black Holes: III. Near-Eddington Accretion
Center for Computational Astrophysics, Flatiron Institute（Flatiron Institute 计算天体物理中心）；School of Natural Sciences, Institute for Advanced Study（高等研究院自然科学学院）；Department of Astronomy, University of Virginia（弗吉尼亚大学天文系）；Virginia Institute for Theoretical Astronomy, University of Virginia（弗吉尼亚大学弗吉尼亚理论天文学研究所）；Michigan SPARC, Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室密歇根SPARC）；Computational Physics and Methods, Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室计算物理与方法部门）；Department of Astrophysical Sciences, Princeton University（普林斯顿大学天体物理科学系）
FORGE'd in FIRE II: The Formation of Magnetically-Dominated Quasar Accretion Disks from Cosmological Initial Conditions
California Institute of Technology（加州理工学院）；University of Otago（奥塔哥大学）；Harvard University（哈佛大学）；Flatiron Institute（平顿研究所）；Wesleyan University（韦斯理安大学）；Northwestern University（西北大学）；University of Connecticut（康涅狄格大学）；University of Toronto（多伦多大学）；Princeton University（普林斯顿大学）
