Compact Objects and Gravitational Radiation

爱因斯坦发现的广义相对论告诉我们，我们日常所熟悉的引力其实是某种更奇怪的东西的表现：物质对时空几何形状的弯曲。该理论的关键预测之一是引力波（GW）的存在：由大质量的快速运动引起的在时空几何中以光速运动的涟漪。虽然引力波对致密双星系统的间接影响已经得到了很好的验证，但直接探测地球上的引力波仍然是一个突出的挑战。实现这种能力的科学回报将是巨大的——从探测爆炸恒星的极端动力学到收集关于宇宙大爆炸时刻的状态的信息。这扇探索宇宙的新窗口耗费了数十年的实验和技术发展，突破了物理科学不同领域的界限。当先进激光干涉引力波天文台（aLIGO）如期达到设计灵敏度时，可能成为首次探测到引力波的辐射爆发已经比最近的恒星半人马座阿尔法星更接近地球。第一次探测到的引力波，以及随后不久的其他探测到的引力波，很可能是在涉及黑洞和/或中子星的双星系统合并过程中产生的。有一种现实的乐观主义认为，在十年之交，将有足够多的这些和其他来源被观测到，从而有信心地说，适当的观测引力波物理学已经到来。当然，这将依赖于精确的干涉测量工程，对极杂数据的巧妙分析，以及最先进的源建模。对于后者，必须继续利用数值相对论的工具来模拟尽可能多的引力波情景，而且还要改进模拟所捕获的物理内容。这个项目中的科学直接支持这项事业，即数值相对论建模，以增强我们对引力辐射源和驱动电磁特征的引力现象的理解。这项提议的研究将产生超出引力波物理学和数值相对论范围的影响。在这个项目中，要想在多信使、计算和数据分析项目中取得成功，需要一个跨天体物理学、计算科学甚至工程的跨学科环境。乔治亚理工学院的相对论天体物理学中心将能够提供这样一个环境，因为它的使命是促进高能天体物理学、天体粒子物理学、宇宙学和引力波物理学之间的研究和教育联系。该奖项支持的研究重点是黑洞和中子星作为引力辐射源的计算建模。该提案考虑了几个涉及天体物理学的项目，这些项目有一个共同点——动态引力和时空曲率所起的关键作用。这些项目中的天体物理现象源于广义相对论万有引力与复杂多物理的结合，涉及流体流动、电磁场、辐射输运和现实状态方程。这项工作还旨在提高我们对天体物理现象的全面理解，而不仅仅是引力波能够告诉我们的，换句话说，电磁和引力波现象导致了多信使观测。研究分为两个方面：1)压缩对象二进制和模拟数据沙盒；2)大质量黑洞对潮汐恒星的破坏。拟议的工作将使博士后和学生有机会与计算科学和工程方面的研究人员互动，开发和实施磁流体动力学的数值算法，处理大型数据集，并参与各种推广活动。在高性能计算、优化、数据分析和软件工程方面获得的经验将进一步推动参与这项工作的年轻研究人员的职业生涯，获得广泛职业所需的宝贵技能。

The General Theory of Relativity discovered by Einstein tells us that the familiar, everyday force of gravity is a manifestation of something much stranger: the bending of the geometry of space-time by matter. Among the key predictions of the theory is the existence of gravitational waves (GW): ripples moving at the speed of light in the geometry of space-time caused by the fast motion of large masses. Although well tested in terms of their indirect effects on binary systems of compact stars, the direct detection of gravitational waves incident on Earth poses an outstanding challenge. The scientific rewards from achieving this ability would be enormous - ranging from probing the extreme dynamics of exploding stars to gleaning information about the state of the Universe almost at the moment of the Big Bang itself. The effort to enable this new window on the universe has occupied several decades of experimental and technological developments that have pushed the boundaries across diverse fields in the physical sciences. When the Advanced Laser Interferometric Gravitational Wave Observatory (aLIGO) reaches designed sensitivity as scheduled, the burst of radiation that may become the first detection of gravitational waves is already closer to the Earth than the closest star, Alfa Centauri. The gravitational waves in this first detection, and others following soon after, were very likely produced during the merger of binary systems involving black holes and/or neutron stars. There is realistic optimism that, at the turn of the decade, enough of these and other sources will be observed to state with confidence that proper observational gravitational wave physics has arrived. This will of course depend on having in place exquisite interferometric engineering, clever analysis of extremely noisy data, and state of the art source modeling. Regarding the latter, it is imperative to continue exploiting the tools of numerical relativity to model not only as many gravitational wave source scenarios as possible, but also to improve the physics content captured by the simulations. The science in this project supports directly this enterprise, namely numerical relativity modeling to enhance our understanding of sources of gravitational radiation and of gravitational phenomena driving electromagnetic signatures. The proposed research will have an impact beyond the confines of gravitational wave physics and numerical relativity. Achieving success in the multi-messenger, computing, and data-analytics projects in this project necessitates an interdisciplinary environment reaching across astrophysics, computing science and even engineering. The Center for Relativistic Astrophysics at Georgia Tech will be capable of providing such an environment since its mission is to foster research and education linking high-energy astrophysics, astro-particle physics, cosmology and gravitational wave physics.This award supports research focused on the computational modeling of black holes and neutron stars as sources of gravitational radiation. The proposal considers several projects that involve astrophysics with a common denominator -- the crucial role played by dynamical gravity and the curvature of space-time. The astrophysical phenomena in these projects arise from a marriage between general relativistic gravitation and complex multi-physics involving fluid flows, electromagnetic fields, radiation transport and realistic equations of state. The effort also aims at enhancing our comprehensive understanding of astrophysical phenomena beyond what gravitational waves alone will be able to tell, in other words, electromagnetic and gravitational wave phenomena leading to multi-messenger observations. The research is organized into two areas: 1) Compact object binaries and a sandbox of simulation data; and 2) Tidal stellar disruptions by massive black holes. The proposed work will give postdocs and students the opportunity to interact with researchers in computing science and engineering, to develop and implement numerical algorithms for magneto-hydrodynamics, work with large data sets and to participate in a variety of outreach activities. The experience gained in high performance computing, optimization, data analytics, and software engineering will further the careers of young researchers participating in the effort, acquiring valuable skills that are in demand in a broad range of professions.