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的区域内与其落在其上的中心物体之间的活动。详细的数值工作，包括第一次所有相关的物理成分，将预测应该观察到什么。该项目承诺，在花了很长时间研究那些根本不起作用的想法后，最终会取得进展，并将在这个前沿研究主题中培训学生。天体物理吸积通常会在有表面的中心物体上进行，在这种情况下，在磁盘的内缘会形成一个边界层。这一层中的能量释放极大地影响了吸积物体的光谱和可变性，这需要一个良好的边界工作模型。这个项目从最近发现的一个重要的新的角动量和质量传输机制开始。传输机制来自引起全球声波的超音速切变流动，这些声波在弱激波中消散。它似乎非常高效和健壮，需要进一步研究。这项工作将识别和探索全三维磁流体(MHD)边界层中的声模特性，其中辐射传递和/或辐射压力的影响是重要的。这项研究使用三维(3D)MHD代码进行了详细的模拟，并对结果进行了仔细的分析，试图找到由声学模式驱动的简单的物理激励运输模型。这项工作的最终结果是一组结合了这些先前探索的物理成分的模拟。这种参数空间探索以了解全球边界层的几何形状和特征，这是以前从未做过的，将导致直接预测可观测量。这些计算将是第一个不依赖自组织角动量输运规则的边界层结构和演化的自洽模型。该项目将特别努力从少数群体和代表性不足的群体中招收学生，为未来的成功培养高素质的人才。这些模拟将产生适合普通公众、公开演讲和一般外展目的的可视化效果。

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.