Theoretical Studies in Gravitation and Astrophysics

LIGO-VIRGO科学合作组织最近报告了前两次引力波（GW）信号的直接探测，并证明这些事件（命名为GW 150914和GW 151226）是由双黑洞的螺旋和合并产生的。这一突破标志着GW天文学时代的开始。他们还提供了最强有力的证据，证明爱因斯坦的广义相对论（GR）是正确的引力理论，并且二元和旋转黑洞的存在具有GR所规定的性质。相对论流体力学（流体在强引力场中以光速运动））和相对论性磁流体力学（流体在磁场中流动）。一个共同的线索连接不同的理论主题是至关重要的作用，引力，特别是相对论引力。致密天体（黑洞、中子星和白色矮星）提供了主要论坛，强引力场中的物质动力学是一个主要主题。研究的一些主题包括致密双星（双黑洞，双中子星和双黑洞-中子星）的螺旋和合并，从致密双星和其他有前途的天体物理源产生GW以及可能伴随它们的电磁信号（例如，这些问题包括：星系和类星体核心中正在合并的超大质量黑洞周围的环绕双星盘（环绕星系和类星体核心中正在合并的超大质量黑洞）、引力坍缩、暗物质（宇宙中物质的主要形式，与正常原子及其成分不同）在星系核心（包括银河系）中超大质量黑洞周围的分布和可观测到的后果。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，PTA和丽莎，以及瞬态事件电磁探测器，如大型综合巡天望远镜（LSST）。因此，除了分析建模之外，该方法还在很大程度上涉及超级计算机上的大规模模拟。关键的工具将是我们强大的和久经考验的伊利诺伊州广义相对论，磁流体动力学（GRMHD）代码。模拟求解了爱因斯坦的重力场方程，耦合到流体的相对论MHD方程和电磁场的麦克斯韦方程。这些方程构成高度非线性，耦合偏微分方程在3+1维，我们解决有限差分。伊利诺斯州的GRMHD代码采用BSSN技术与移动穿刺计的条件来解决场方程和高分辨率，冲击捕获计划的MHD。要解决的问题包括初始值和演化计算，并处理包含黑洞的真空时空，以及包含现实物质源，磁场和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").