Mergers, Stars, and Disks: Dense Matter Phenomena in Numerical Relativity

通过研究中子星之间的碰撞或中子星与黑洞的碰撞，我们可以对强引力的极端情况、比原子核更致密的物质，甚至重元素的起源有很多了解。 最近在引力波和电磁波谱中观察到了两颗中子星的合并。 天文学家现在知道，这样的事件发生了，它们释放出大量的辐射和物质，但这种释放在合并后究竟是如何发生的仍然不清楚。包括广义相对论在内的数值模拟是预测合并过程如何展开的唯一方法，但由于湍流的存在，这些模拟变得非常困难，湍流在很大范围的长度尺度上产生了流体流动和磁场特征。 小规模的流动确实会在大规模上推动合并残余的变化，因此不能忽视。 虽然计算机模拟还不能直接捕捉到所有这些动态，但通过对未解决的小规模效应和合并后初始状态的参数化探索，可以利用当前的计算能力学到很多东西。 本项目将采用这些策略来阐明这些奇异的和暴力的事件是如何产生流出和辐射的。 进行这些模拟将涉及对研究生和本科生进行相对论天体物理学计算机建模技术的培训。由此产生的引力波和核碎片数据将提供给所有致力于探测和描述这些事件的天文学家。华盛顿州立大学将研究数值相对论的三个核心问题--螺旋双星、差动旋转中子星和超吸积黑洞--使用爱因斯坦谱代码（SpEC），这是一个高精度的数值相对论代码，包括磁流体力学、核微观物理、和中微子的传输 Inspiral模拟将研究状态方程对引力波的影响，并将探索进化算法的改进和状态方程参数化的平滑因果关系。 NSNS系统的合并后动力学将被建模，重点是超大质量中子星星残骸的情况。 模拟将跟踪长期演化的影响下，中微子辐射，大规模的磁场和亚网格尺度的湍流崩溃。 最后，将使用中微子输运方法分析黑洞-环面系统周围的中微子效应。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

A great deal can be learned about the extremes of strong gravity, about denser-than-nuclei matter, and even about the origin of heavy elements by studying the collisions of neutron stars with each other or with black holes. One such merger of two neutron stars has recently been observed in gravitational waves and across the electromagnetic spectrum. Astronomers now know that such events happen and that they release tremendous amounts of radiation and material, but exactly how this release happens in a merger aftermath remains unclear. Numerical simulations that include general relativity are the only way to predict how merger processes unfold, but these simulations are made incredibly difficult by the presence of turbulence, which creates fluid flow and magnetic field features across a wide range of length scales. Small-scale flows do drive changes in the merger remnant at large scales and so cannot be ignored. Although computer simulations cannot yet directly capture all of this dynamics, a great deal can be learned with current computing capabilities by parameterized exploration of unresolved small-scale effects and post-merger initial states. This project will pursue these strategies to shed light on how these exotic and violent events produce their outflows and radiation. Carrying out these simulations will involve training both graduate and undergraduate students on techniques of computer modeling in relativistic astrophysics. The resulting gravitational wave and nuclear debris data will be made available to all astronomers working to detect and characterize these events.The Washington State University will study three core problems of numerical relativity--inspiraling binaries, differentially rotating neutron stars, and hyperaccreting black holes--using the Spectral Einstein Code (SpEC), a high-accuracy numerical relativity code that includes magnetohydrodynamics, nuclear microphysics, and neutrino transport. Inspiral simulations will study equation of state effects on gravitational waves, and improvements to evolution algorithms and smooth, causal equation of state parameterizations will be explored. Post-merger dynamics of NSNS systems will be modeled, focusing on the case of a hypermassive neutron star remnant. Simulations will track the secular evolution to collapse under the influence of neutrino radiation, large-scale magnetic fields, and subgrid-scale turbulence. Finally, neutrino effects around black hole-torus systems will be analyzed using neutrino transport methods.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.