Theoretical Studies in Gravitation and Astrophysics

LIGO-VIRGO科学合作组织最近报告了首次直接探测到的引力波（GW）信号，并证明了这些事件（命名为GW150914和GW151226）是由双黑洞的启发和合并产生的。这一突破标志着GW天文学时代的开始。它们还提供了迄今为止最有力的证据，证明爱因斯坦的广义相对论（GR）是正确的引力理论，双黑洞和旋转黑洞的存在具有GR规定的性质。该项目资助的研究涵盖了几个问题，包括广义相对论、gw的产生、相对论流体力学（流体在强引力场中流动并以光速运动）和相对论磁流体力学（流体在磁场中流动）。连接不同理论主题的一条共同线索是引力，特别是相对论引力的关键作用。紧凑的物体（黑洞、中子星和白矮星）提供了主要的论坛，强引力场中的物质动力学是一个主要的主题。一些研究课题包括紧致双星（双黑洞、双中子星和双黑洞-中子星）的启发和合并，从紧致双星和其他有前途的天体物理源产生的GWs以及可能伴随它们的电磁信号（例如伽马射线暴），引力坍缩，星系和类星体核心合并超大质量黑洞周围的环双星盘，以及包括银河系在内的星系核心中超大质量黑洞周围暗物质（宇宙中物质的主要形式，与普通原子及其成分不同）的轮廓和可观察到的后果。这些结果对天文观测具有重要意义，包括计划用于GW干涉仪的观测，如高级LIGO/VIRGO网络、GEO、KAGRA、PTAs和LISA，以及瞬态事件电磁探测器，如大型天气巡天望远镜（LSST）。这些主题大多代表了理论物理中长期存在的基本问题，需要大规模的计算来解决。因此，除了分析建模之外，该方法在很大程度上还涉及在超级计算机上进行大规模模拟。关键工具将是我们稳健且经过良好测试的伊利诺伊广义相对论磁流体力学（GRMHD）代码。模拟求解了爱因斯坦的引力GR场方程、流体的相对论MHD方程和电磁场的麦克斯韦方程组。这些方程构成了高度非线性的，耦合的3+1维偏微分方程，我们用有限差分法求解。伊利诺伊GRMHD代码采用BSSN技术与移动穿刺计条件来求解场方程，并为MHD提供了高分辨率的冲击捕获方案。要解决的问题包括初始值和进化计算，并处理包含黑洞的真空时空，以及包含现实物质源，磁场以及电磁和中微子辐射的时空（“多信使天文学”）。

The LIGO-VIRGO Scientific Collaboration recently reported the first two direct detections of gravitational wave (GW) signals and demonstrated that these events (named GW150914 and GW151226) were produced by the inspiral and coalescence of binary black holes. This breakthrough marks the beginning of the era of GW astronomy. They also provide the strongest evidence yet that Einstein's theory of general relativity (GR) is the correct theory of gravity and that binary and spinning black holes exist with the properties prescribed by GR. The research funded within this project spans several problems involving GR, the generation of GWs, relativistic hydrodynamics (fluid flow in strong gravitational fields and moving at the speed of light)) and relativistic magnetohydrodynamics (fluid flow in magnetic fields). A common thread uniting the different theoretical topics is the crucial role of gravitation, especially relativistic gravitation. Compact objects (black holes, neutron stars and white dwarfs) provide the principal forum, and the dynamics of matter in a strong gravitational field is a major theme. Some of the topics for investigation include the inspiral and coalescence of compact binaries (binary black holes, binary neutron stars and binary black hole--neutron stars), the generation of GWs from compact binaries and other promising astrophysical sources and the electromagnetic signals that may accompany them (e.g., gamma-ray bursts), gravitational collapse, circumbinary disks around merging supermassive black holes in the cores of galaxies and quasars, and the profile and observable consequences of dark matter (the major form of matter in the universe and unlike normal atoms and their constituents) around supermassive black holes in galaxy cores, including the Milky Way. The results have important implications for astronomical observations, including those planned for GW interferometers, such as the Advanced LIGO/VIRGO network, GEO, KAGRA, the PTAs and LISA, and transient-event electromagnetic detectors, such as the Large Synoptic Survey Telescope (LSST).Most of these topics represent long-standing, fundamental problems in theoretical physics requiring large-scale computation for solution. Hence the approach involves to a significant degree large-scale simulations on supercomputers, in addition to analytical modeling. The key tool will be our robust and well-tested Illinois general relativistic, magnetohydrodynamic (GRMHD) code. The simulations solve Einstein's field equations of GR for gravity coupled to the equations of relativistic MHD for the fluid and Maxwell's equations for the electromagnetic fields. These equations constitute highly nonlinear, coupled partial differential equations in 3+1 dimensions that we solve by finite-differencing. The Illinois GRMHD code employs the BSSN technique with moving puncture gauge conditions to solve the field equations and a high-resolution, shock capturing scheme for the MHD. The problems to be tackled comprise both initial value and evolution computations and treat vacuum spacetimes containing black holes, as well as spacetimes containing realistic matter sources, magnetic fields and both electromagnetic and neutrino radiation ("multimessenger astronomy").