Dynamical encounters and black hole mergers in gaseous environments

最近对引力波（GW）的探测显示，宇宙中黑洞（BH）-BH和中子星星（NS）-NS的合并率很高，分别为23.9+-14.9 Gpc^-3 yr^{-1}和320 Gpc^-3 yr^{-1}。最大的挑战是了解可能导致合并的天体物理机制，以及GW观测如何区分这些通道。现有的观测事件的天体物理起源的理论模型目前要么是高度不完整的或在紧张的数据，这暗示需要重大的理论改进建模GW源人口。我们超越了现有的半分析方法来模拟合并活动星系核吸积盘，并作出预测的GW源人口和可能的电磁签名。我们将开发3D流体动力学模拟，以详细研究最相关的物理过程，并开发一个更准确的吸积盘分析模型，同时考虑到嵌入的致密物体对盘的影响。我们将把结果纳入我们的半分析模型，使其更加准确。这也将铺平道路，以构建一个完全自洽的模拟恒星，恒星质量的紧凑对象，和AGN吸积盘的共同演化。我们超越了现有的半分析方法来模拟合并活动星系核吸积盘，并作出预测的GW源人口和可能的电磁签名。我们将开发3D流体动力学模拟，以详细研究最相关的物理过程，并开发一个更准确的吸积盘分析模型，同时考虑到嵌入的致密物体对盘的影响。我们将把结果纳入我们的半分析模型，使其更加准确。这也将铺平道路，以构建一个完全自洽的模拟恒星，恒星质量的紧凑对象，和AGN吸积盘的共同演化。我们在项目期间重点做好以下工作。1. Tagawa et al 2020指出，活动星系核中的大多数合并双星都是在气体环境中的单-单捕获过程中形成的。我们研究了这个过程与流体力学模拟与大量的点粒子.盘交叉双星-研究动力学摩擦对双星交叉吸积盘的影响，以研究双星弛豫到盘中的效率。双星倾角对齐-检查双星轨道倾角如何演变时，双星嵌入吸积盘，以确定预期的水平之间的对准双星单或双星双星的相互作用。气体中的双星-单星和双星-双星相互作用-研究当双星嵌入吸积盘时，动力学相互作用是如何改变的。多体系统中的间隙打开和吸积流-检查气体盘和嵌入盘中的几个物体之间的角动量交换，以确定在盘中打开环形空腔的条件。检查打开差距的条件如何取决于单个对象和二进制对象（如果存在于狭窄的半径范围内）的数量。此外，如果差距中存在多个物体，则检查穿过差距到物体上并进入内部区域以馈送SMBH（例如Jiang+ 2014）的流量。

Recent detections of gravitational waves (GWs) have shown evidence for a high rate of black hole (BH)-BH and neutron star (NS)-NS mergers in the Universe, finding 23.9+-14.9 Gpc^-3 yr^{-1} and 320 Gpc^-3 yr^{-1}. The great challenge is to understand the possible astrophysical mechanisms that may lead to mergers and how GW observations can discriminate between these channels. Existing theoretical models of the astrophysical origin of the observed events are currently either highly incomplete or in tension with data which hints at the need for major theoretical improvements of modeling GW source populations. We move beyond the existing semianalytical methods to model mergers in AGN accretion disks and to make predictions for the GW source populations and possible electromagnetic signatures. We will develop 3D hydrodynamical simulations to investigate the most relevant physical processes in detail and develop a more accurate analytical model of the accretion disk taking into account the influence of the embedded compact objects on the disk. We will incorporate the results in our semianalytical models to make them more accurate. This will also pave the way to construct a fully self-consistent simulation of the coevolution of stars, stellar mass compact objects, and AGN accretion disks. We move beyond the existing semianalytical methods to model mergers in AGN accretion disks and to make predictions for the GW source populations and possible electromagnetic signatures. We will develop 3D hydrodynamical simulations to investigate the most relevant physical processes in detail and develop a more accurate analytical model of the accretion disk taking into account the influence of the embedded compact objects on the disk. We will incorporate the results in our semianalytical models to make them more accurate. This will also pave the way to construct a fully self-consistent simulation of the coevolution of stars, stellar mass compact objects, and AGN accretion disks. We focus on the following undertakings during the project.1. Gas-capture binary formation Tagawa et al 2020 has pointed out that most of the merging binaries in AGN are those which form during single-single captures in gasous environments. We investigate this process with hydrodynamics simulations with massive point particles.2. Disk crossing binaries- Investigate the effects of dynamical friction on a binary crossing an accretion disk to investigate the efficiency of the relaxation of the binary into the disk.3. Binary inclination alignment- Examine how the binary orbital inclination evolves when the binary is embedded in the accretion disk, to determine the expected level of alignment between binary-single or binary-binary interactions.4. Binary-single and binary-binary interaction in gas- Examine how the dynamical interactions are altered when the binary is embedded in the accretion disk.5. Gap opening and accretion flow in multibody systems- Examine the angular momentum exchange between the gaseous disk and several objects embedded in the disk to determine the conditions to open an annular cavity in the disk. Examine how the conditions for opening the gap depends on the number of single objects and binaries if present in a narrow range of radii. Further, examine the flow across the gap onto the objects and into the inner region to feed the SMBH (e.g. Jiang+ 2014) if multiple objects are present in the gap.