Collaborative Research: Accretion Dynamics of Black Hole Mergers

据估计，在宇宙中的某个地方，每年都会有几对超大质量黑洞合并，在发生合并的星系中心留下一个质量更大的单一黑洞。释放出的能量是巨大的，对星系演化的影响也是深远的，但从来没有发现过这样的事件，因为绝大多数的能量是以引力波的形式释放的，而引力波到目前为止还无法检测到。这个项目将使用复杂的数值模拟来表征事件影响下附近气体应该发出的可见光信号。这些技术的训练将对团队中的初级研究人员未来的活动非常有价值。尽管在合并事件附近应该有足够的气体发出可见辐射，但任何发出的信号的性质都是未知的。具体的问题包括大多数光将出现在哪个波段，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。周围气体与相互束缚的一对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、激波和动力学时空，这些只能用数值方法来解决。这需要使用辐射传输后处理的精心构建的模拟来预测关键的可观测特征，使用该团队的新基础设施，该基础设施支持在不同的网格和性质不同的时空上进行一致的MHD计算。用天体物理上看似合理的参数进行计算，应该可以识别独特的光子信号，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训一些研究生和博士后研究员，这些技能的价值远远超出了天体物理研究的范围。该小组积极接触非理科学生和普通公众，包括让聋哑人和重听学生参与科学工作。

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.