Dynamical, Strong-field Gravity

该项目的研究目标是了解爱因斯坦广义相对论的强场机制。这包括天体物理学和广义相对论的理论两个方面。在天体物理方面，主要工作是对双星黑洞、黑洞-中子星和双星中子星碰撞进行数值模拟。这对于支持最近由LIGO探测到的两个黑洞碰撞而开启的引力波天文学领域非常重要。这类信号源的数值模型对于辅助探测是必要的，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极端相对论极限；即当两个黑洞以光速碰撞时会发生什么。对结果的猜测始于20世纪60年代的S，当时彭罗斯利用这一情景来帮助阐述他的宇宙审查猜想，他说，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解决广义相对论这一制度的工具。这些项目的实施将涉及研究生、本科生和博士后研究员。他们将接受培训，从事领先的科学研究，在相应的物理领域变得知识渊博，并熟练掌握高性能计算和数值方法。这些技能对许多职业来说是无价的，因此也将有益于并进一步促进那些随后希望在学术之外追求职业生涯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包括：(1)了解中子星和黑洞-中子星合并中中子星自转的后果，(2)当有大量抛射物质时，改进涉及中子星的碰撞中重元素产额和相应电磁对应发射的估计，(3)开始包括中微子和辐射传输，并在我们的演化代码中改进我们的磁场模型，与涉及中子星的合并相关，(4)继续开发偏心双星的参数化后爱因斯坦(PPE)框架，以允许此类事件(如果观察到)用于测试广义相对论，以及(5)探索引力的替代理论和/或广义相对论中黑洞的奇异替代方案(如玻色子星)中的二元合并，以允许LIGO最近探测到的合并事件和未来的探测来约束/排除/发现这些替代方案。对于极端相对论碰撞问题，接近这一极限的途径将是开发一个代码来研究零尘埃分布的碰撞。这样的分布可以被定制为以一种非奇异的方式接近点-质点和平面-平行波碰撞极限，并服从完全的数值处理。

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.