Numerical Simulations of Compact Neutron Star Binary Mergers

中子星和黑洞的碰撞是非常罕见的事件，但它们在引力波、红外辐射、X射线和伽马射线中释放的巨大能量使它们即使在非常遥远的地方也有可能被探测到。 它们的引力波和电磁信号包含有关碰撞物体的属性和未知物理的信息，但为了提取这些信息，天文学家需要理论模型来进行比较。 在这个项目中，将对黑洞和中子星星相互环绕并最终合并的系统进行计算机模拟。 模拟还将探索黑洞-中子星星和中子星-中子星星合并通常产生的碎片：放射性气体喷射到周围的空间和热，磁化核物质围绕黑洞旋转。 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。 这项研究填补了黑洞中子星星二进制合并的inspiral，磁盘和流出阶段的模拟与频谱爱因斯坦代码（SpEC），一个高精度的数值相对论代码，现在包括磁流体力学，核微观物理和中微子冷却的一些最有趣的剩余空白。 长吸气的模拟用于测试和改进用于检测和识别来自此类源的引力波信号的算法。 改进SpEC对黑洞视界附近流动的处理，可以实现更高精度的吸积盘模拟，这些模拟用于研究盘动力学、伽马射线爆发、能量提取和后期（十分之一秒）行为。 该项目研究了各种二元参数的流出量。 喷出物远离合并后的黑洞的演变跟踪平滑粒子流体动力学和核反应网络代码使用SpEC数据作为输入，使预测的回落，kilonova亮度，和核合成。

Collisions of neutron stars and black holes are very rare events, but the enormous energies they release in gravitational waves, infrared radiation, X-rays, and gamma-rays make them potentially detectable even when very far away. Their gravitational wave and electromagnetic signals contain information about the properties and unknown physics of the colliding objects, but to extract this information, astronomers need theoretical models to which they can compare. For this project, computer simulations will be carried out of systems with a black hole and neutron star orbiting each other and eventually merging. Simulations will also explore the debris commonly produced by black hole-neutron star and neutron star-neutron star mergers: radioactive gas ejected into the surrounding space and hot, magnetized nuclear matter swirling around a black hole. 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. This research fills some of the most interesting remaining gaps in the modeling of inspiral, disk, and outflow phases of black hole-neutron star binary mergers using simulations with the Spectral Einstein Code (SpEC), a high-accuracy numerical relativity code that now includes magnetohydrodynamics, nuclear microphysics, and neutrino cooling. Simulations of long inspirals are used to test and improve algorithms for detecting and identifying the gravitational wave signals from such sources. Improvements to SpEC's treatment of flows near black hole horizons enable higher-accuracy accretion disk simulations, and these are used to study the disk dynamics, gamma ray burst, energy extraction, and late-time (tenths of a second) behavior. The project studies outflows for a wide range of binary parameters. The evolution of ejecta far from the post-merger black hole is tracked with smoothed-particle hydrodynamics and nuclear reaction network codes using SpEC data as input, enabling predictions of fallback, kilonova brightness, and nucleosynthesis.