Constraining the Magneto-Rotational Instability in Accretion Disks with Simulations of Dwarf Novae and X-ray Binary Outbursts

物质落在矮星、中子星和黑洞上，这一过程被称为吸积，为一些最具能量和最迷人的天文来源提供了动力。因为旋转在宇宙中很常见，大多数吸积系统都形成了围绕中心重力物体旋转的圆盘，在那里物质必须在继续向内移动之前转移其旋转惯性或角动量。向内流动的物质也会在圆盘上花费时间将能量转化为向外辐射，从而可以观察到这些物体。这项研究将应用新的方法来理解白矮星周围圆盘的角动量输运过程，并可能最终确定目前占主导地位的模型是否正确。磁旋转不稳定性（MRI）湍流已经成为理解角动量输运和吸积盘中吸积能量释放的主要研究框架，在所有天体物理学中，从原行星盘到活动星系核。虽然最终的目标是模拟观测到的源，但迄今为止很少有人关注围绕白矮星运行的吸积盘中的矮新星爆发，这为角动量输运提供了最有趣的观测约束。利用垂直分层、辐射磁流体动力学（MHD）剪切箱模拟MRI湍流，本研究将建立在最近的间歇性热对流结果的基础上。计划进行三项新的研究：(1)确保热对流得到数值解析，并了解它如何增强湍流输运；(2)在大部分中性状态下纳入非理想MHD，以观察MRI湍流输运是否可以在静态状态下持续；(3)将关于垂直结构和角动量输运的经验教训纳入现有的基于α的氢电离盘不稳定性模型。MRI模型与观测结果的直接对抗将巩固氢电离盘不稳定性的理论基础，并使矮新星和低质量x射线双星的观测能够更有效地约束MRI湍流的性质。一名研究生将根据该项目撰写论文，几名本科生预计将参与其中，研究将为公开演讲提供信息，包括一项专门针对这项工作所包含的科学的新研究。

Material falling onto dwarf stars, neutron stars, and black holes, a process called accretion, powers some of the most energetic and fascinating astronomical sources. Because rotation is common in the Universe, most accretion systems form disks swirling around the central gravitating object, where material must transfer away its rotational inertia, or angular momentum, before continuing inwards. The matter flowing inwards also spends time in the disk converting energy into the outgoing radiation by which these objects can be observed. This research will apply new methods to understanding the process of angular momentum transport in disks around white dwarf stars, and may finally settle whether the currently dominant model is in fact correct.Magneto-rotational instability (MRI) turbulence has become the dominant research framework for understanding angular momentum transport and the release of accretion power in accretion disks across all of astrophysics, from proto-planetary disks to active galactic nuclei. Although the ultimate goal is to model observed sources, little attention has been paid so far to dwarf nova outbursts in accretion disks orbiting white dwarfs, which offer the most interesting observational constraints on angular momentum transport. Using vertically-stratified, radiation magneto-hydrodynamic (MHD) shearing box simulations of MRI turbulence, this research will build on recent results showing intermittent thermal convection. Three new studies are planned: (1) ensure that the thermal convection is numerically resolved, and understand how it enhances turbulent transport, (2) incorporate non-ideal MHD in the largely neutral state to see if MRI turbulent transport can be sustained in the quiescent state; and (3) incorporate lessons learned about the vertical structure and angular momentum transport into existing alpha-based models of the hydrogen ionization disk instability. This direct confrontation between the MRI model and observations will firm up the theoretical foundation of the hydrogen ionization disk instability, and allow observations of dwarf novae and low mass X-ray binaries to constrain more effectively the properties of MRI turbulence.One graduate student will develop their thesis from this project, several undergraduates are expected to be involved, and the research will inform public talks, including a new one being developed specifically on the science contained in this work.