Collaborative Research: Accretion Dynamics of Black Hole Mergers

据估计，在宇宙的某个地方，每年都会有几对超大质量黑洞合并，在发生这种情况的星系中心留下一个更大的黑洞。释放的能量是巨大的，对星系演化的影响是深远的，但由于绝大多数能量是以引力波的形式释放的，迄今为止还无法探测到，因此没有发现这样的事件。这个项目将利用复杂的数值模拟来描述在事件影响下附近气体应该发出的可见光信号。这些技术的培训对于团队中初级研究人员的未来活动将有很大的价值。虽然在合并事件附近应该有足够多的气体发出可见辐射，但任何发射信号的特征都是未知的。具体的问题包括大部分的光会在哪个波段出现，它的光谱是什么，以及辐射功率如何随时间变化？这项工作将开始回答这些问题。周围气体和一对相互束缚的黑洞之间极其复杂的相互作用涉及到强烈的非线性物理，包括磁流体动力学（MHD）湍流、冲击和动态时空，这些只能用数值来解决。这需要使用辐射传输后处理来预测关键的可观察特征，使用团队的新基础设施来支持在不同网格和不同时空上一致的MHD计算。利用天体物理学上合理的参数进行计算，应该可以识别出独特的光子信号，以便观察者在黑洞合并的过程中定位它们。这个计算系统也应该对许多其他天体物理模拟有用。这项工作将在大规模数值模拟技术方面培养一批研究生和博士后，这些技术的价值远远超出了天体物理学研究的范围。该团队积极向非理科生和公众推广，包括让失聪和听力障碍的学生参与科学。

It is estimated that somewhere in the universe a few pairs of supermassive black holes merge every single year, leaving behind a still more massive single black hole at the centers of the galaxies where this occurs. The energy released is enormous, and the effect on galactic evolution profound, but no such event has ever been identified because the overwhelming majority of the energy is released in gravitational waves, which are as yet undetectable. This project will characterize the visible light signals that should be given off by nearby gas under the influence of the event, using complex numerical simulations. Training in these techniques will be of great value for the future activities of the junior researchers on the team.Although there should be sufficient gas close enough to the merger events to give off visible radiation, the character of any emitted signals is unknown. Particular questions include in which band most of the light will emerge, what is its spectrum, and how does the radiated power vary in time? This work will start to answer these questions. The extremely complex interaction between the surrounding gas and a pair of black holes bound to one another involves strongly nonlinear physics, including magnetohydrodynamic (MHD) turbulence, shocks, and dynamical spacetimes, which can only be tackled numerically. This requires carefully structured simulations using radiation transfer post-processing to predict key observable features, using the team's new infrastructure that supports consistent MHD calculations on separate grids and across qualitatively different spacetimes. Calculations with astrophysically plausible parameters should identify unique photon signals for observers to locate black holes on their way to merger.This computational system should also be useful to many other astrophysical simulations. The work will train a number of graduate students and post-doctoral fellows in the techniques of large-scale numerical simulation, skills that are valuable far beyond the confines of astrophysical research. The team is active in outreach both to non-science students and to the general public, including work to engage deaf and hard-of-hearing students in the sciences.