Between the Disk and the Star: Boundary Layers in Astrophysical Accretion Disks

这项研究将探索一种诱人的新机制，来解释物质向内流动和它落在中心物体之间的区域内的活动。详细的数值计算将首次包括所有相关的物理成分来预测应该观察到什么。这个项目在花费了很长时间的想法之后，最终有望取得进展，它将在这个前沿的研究课题上培养学生。天体物理吸积通常发生在有表面的中心物体上，在这种情况下，在圆盘的内缘形成边界层。该层的能量释放极大地影响吸积物体的光谱和变异性，这需要一个良好的边界工作模型。这个项目开始于最近发现的角动量和质量在这个区域传递的重要新机制。传递机制来自于超音速剪切流，这种剪切流产生的声波在弱冲击中消散。它似乎是非常有效和稳健的，需要进一步研究。这项工作将识别和探索全三维磁流体动力学（MHD）边界层中声学模式的特性，其中辐射传递和/或辐射压力的影响是重要的。这项研究包括使用三维（3D） MHD代码的详细模拟和对结果的仔细分析，试图找到由声学模式驱动的简单物理驱动的传输模型。这项工作的高潮是一组模拟，结合了这些先前探索的物理成分。这种参数空间探索，以了解边界层的整体几何形状和特征，是以前从未做过的，并将导致可观测量的直接预测。这些计算将是第一个不依赖于特别角动量输运处方的边界层结构和演化的自洽模型。该项目将特别努力招收少数民族和代表性不足群体的学生，为未来的成功培养高素质的人才。模拟将产生适合公众、公开演讲和一般推广目的的可视化效果。

This study will explore a tantalizing new mechanism for explaining activity within the region between an inward flow of material and the central object onto which it is falling. Detailed numerical work including for the first time all of the relevant physical ingredients will predict what should be observed. The project promises finally to make progress after a long time spent on ideas that simply did not work, and it will train students in this cutting-edge research topic.Astrophysical accretion often proceeds onto a central object with a surface, in which case a boundary layer forms at the inner edge of the disk. Energy release in this layer dramatically affects the spectra and variability of accreting objects, which requires a good working model of the boundary. This project starts with a recently discovered important new mechanism for angular momentum and mass transport across this region. The transport mechanism comes from supersonic shear flows that give rise to global acoustic waves that dissipate in weak shocks. It appears to be very efficient and robust, and needs to be further studied. This work will identify and explore the properties of acoustic modes in fully three-dimensional, magneto-hydrodynamic (MHD) boundary layers, in which the effects of radiation transfer and/or radiation pressure are important. The study involves detailed simulations using a three-dimensional (3D) MHD code and careful analysis of the results, trying to find simple physically motivated models of transport driven by acoustic modes. The culmination of the work is a set of simulations combining these previously explored physical ingredients. This parameter space exploration to understand the global geometry and characteristics of the boundary layer has never been done before, and will lead to direct prediction of observable quantities. These calculations will be the first self-consistent model of the structure and evolution of boundary layers not relying on ad-hoc angular momentum transport prescriptions.The project will make special efforts to recruit students from minority and underrepresented groups, training personnel highly qualified for future success. The simulations will result in visualizations appropriate for the general public, for public talks and general outreach purposes.