Dynamical, Strong-field Gravity

该项目的研究目标集中在理解爱因斯坦广义相对论的强场制度。这包括天体物理学和广义相对论的理论方面。在天体物理方面，主要的工作是对双黑洞、黑洞-中子星和双中子星碰撞的数值模拟。这对于支持引力波天文学领域是很重要的，引力波天文学是由LIGO探测到两个黑洞的碰撞而开创的。这类信号源的数值模型需要帮助进行探测，并且对于破译观测信号的细节至关重要。在理论方面，关于极端情况下时空的性质有许多悬而未决的问题。这里主要关注的是黑洞碰撞的超相对论性极限；也就是说，当两个黑洞以光速相撞时会发生什么。关于这个结果的猜测始于20世纪60年代，当时彭罗斯用这个场景来帮助形成他的宇宙审查猜想，该猜想认为时空中的所有奇点都隐藏在事件视界之后。数值方法现在为我们提供了明确处理广义相对论的工具。这些项目将涉及研究生、本科生和博士后。他们将被训练去做领先的科学研究，成为在物理的相应领域的知识，并熟练的高性能计算和数值方法。这些技能对许多职业来说都是无价的，因此也将有利于并促进那些随后希望在学术界以外从事职业的学生和博士后的发展。将进行的引力波源建模项目的具体清单是：(1)了解中子星自旋在双中子星和黑洞-中子星合并中的后果；(2)改进对涉及中子星的碰撞中重元素产量和相应电磁对应发射的估计，当存在大量弹出物质时；(3)开始包括中微子和辐射输运。(4)继续发展偏心双星的参数化后爱因斯坦（ppE）框架，如果观测到这样的事件，就可以用来测试广义相对论；(5)在广义相对论中探索引力替代理论和/或黑洞的奇异替代理论（如玻色子星）中的双星合并；允许LIGO最近探测到的并合事件和未来的探测来约束/排除/发现这些替代方案。对于超相对论性碰撞问题，接近这一极限的途径将是通过开发一个代码来研究零尘分布的碰撞。这样的分布可以被调整为以非奇异的方式接近点粒子和平面平行波碰撞极限，可以进行完整的数值处理。

The research goals of this project are focused on understanding the strong-field regime of Einstein's theory of general relativity. This encompasses both astrophysical and theoretical aspects of general relativity. On the astrophysical side, the main effort is numerical simulations of binary black hole, black hole-neutron star and binary neutron star collisions. This is important to support the field of gravitational wave astronomy recently ushered in by LIGO's detection of the collision of two black holes. Numerical models of such sources are needed to aid in detection, and are crucial to decipher details of observed signals. On the theoretical side, there are many outstanding questions about the nature of spacetime in extreme situations. The one that will be the main focus here is the ultra-relativistic limit of black hole collisions; namely, what happens when two black holes collide at the speed of light. Speculation about the outcome began in the 1960's when Penrose used this scenario to help formulate his cosmic censorship conjecture, stating all singularities in spacetime are hidden behind event horizons. Numerical methods are now giving us the tools to definitively tackle this regime of general relativity. The pursuit of these projects will involve graduate students, undergraduates and postdoctoral fellows. They will be trained to do leading scientific research, become knowledgeable in corresponding areas of physics, and adept in high-performance computing and numerical methods. These skills are invaluable to many professions, and would thus also benefit and further the development of those students and postdocs that subsequently wish to pursue careers outside academia.A specific list of gravitational wave source modeling projects that will be pursued are (1) understanding the consequences of neutron star spin in binary neutron star and black hole-neutron star mergers, (2) improving estimates of heavy element yields and corresponding electromagnetic counterpart emission in collisions involving neutron stars when there is significant ejected material, (3) beginning to include neutrino and radiation transport, and improving our models of magnetic fields in our evolution code, relevant for mergers involving neutron stars, (4) continued development of the parameterized post Einsteinian (ppE) framework for eccentric binaries to allow such events, if observed, to be used to test general relativity, and (5) explore binary mergers in alternative theories of gravity and/or exotic alternatives to black holes within general relativity (such as boson stars), to allow the merger event recently detected by LIGO and future detections to constrain/rule-out/discover these alternatives. Regarding the ultra-relativistic collision problem, the route to approaching this limit will be by developing a code to study the collision of distributions of null dust. Such distributions can be tailored to approach both the point-particle and plane-parallel wave collision limits in a non-singular manner amenable to full numerical treatment.