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

通过研究中子星之间或与黑洞的碰撞，可以了解许多关于强引力的极端情况，关于密度比原子核更大的物质，甚至关于重元素的起源。最近在引力波和整个电磁光谱中观察到了两颗中子星的合并。天文学家现在知道，这种事件会发生，它们会释放出大量的辐射和物质，但这种释放在合并后到底是如何发生的，目前尚不清楚。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，这些模拟变得极其困难，这会在广泛的长度尺度上产生流体流动和磁场特征。小规模的资本流动确实推动了大规模并购剩余的变化，因此不能被忽视。尽管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的初始状态进行参数化探索，可以从当前的计算能力中学到很多东西。该项目将采用这些战略，以阐明这些外来和暴力事件是如何产生其外流和辐射的。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中的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。华盛顿州立大学将使用谱爱因斯坦代码(SPEC)来研究数值相对论的三个核心问题--激发双星、差动旋转中子星和超吸积黑洞。SPEC是一种高精度的数值相对论代码，包括磁流体动力学、核微物理和中微子传输。螺旋模拟将研究状态方程对引力波的影响，并将探索对演化算法和平滑、因果状态方程参数化的改进。将对NSNS系统合并后的动力学进行建模，重点是超大质量中子星残留物的情况。模拟将跟踪在中微子辐射、大尺度磁场和亚网格尺度湍流影响下的长期演化到坍塌。最后，将使用中微子传输方法分析围绕黑洞-环面系统的中微子效应。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.