GPU-enabled General Relativistic Simulations of Jetted Tidal Disruptions of Stars by Supermassive Black Holes

潮汐破坏事件（TDEs）发生在恒星被超大质量黑洞的引力场摧毁时，是对静止超大质量黑洞（SMBHs）特性的独特探索。到目前为止，大约有30个被观测到，这个数字在调查和新仪器的帮助下正在稳步增长。尽管我们拥有如此丰富的观测知识，但我们对TDE物理学的理解（这将最终使我们能够解释这些观测结果）充其量仍处于初级阶段。特别是，我们仍然不明白是什么原因导致碎片失去能量和角动量，落入黑洞并辐射。这个项目将利用这样一个事实，即在其核心，tde最终是由广义相对论磁流体动力学（GRMHD）运动方程很好地描述的。通过对TDE进行直接的GRMHD模拟，该项目希望获得对TDE物理的第一性原理理解。提议的模拟将为TDE社区中几个长期存在的问题提供答案：碎片是如何循环、耗散能量和吸积到SMBH的？恒星气体的哪一部分形成了圆盘，哪一部分作为流出物被喷射出来，这些部分是如何依赖于黑洞的质量、自旋和恒星轨道的倾角的？偏心吸积盘是如何形成的，角动量是如何在这样的盘中传递的？如果这样一个偏心圆盘是倾斜的，就像在tde中自然预期的那样，它会经历广义相对论的进动吗？这样的圆盘会产生相对论性喷流吗？了解这些问题将使社区能够对TDE观察结果做出有意义的定量解释。尽管该项目的重点是tde，但它阐明了倾斜吸积盘及其喷流的基本物理特性，这些特性适用于一系列源，包括类星体、黑洞双星和超亮x射线源。此外，所提出的模拟将首次从第一流原理出发，研究偏心倾斜吸积盘中磁旋不稳定性的发展，以及在碎屑流的持续进料下这些盘的长期演化和GR进动。此外，被黑洞撕碎并产生相对论性喷流的恒星提供了广义相对论的一些最迷人的表现。该项目将通过公开讲座、暑期学校、广播电台和报纸采访以及新闻稿等方式传播作为该提案一部分的研究成果。最后，该项目将让本科生参与数据分析和可视化，他们将获得使用大数据、黑洞吸积和射流物理的经验，在会议上展示他们的成果，并在同行评审的期刊上发表他们的工作。

Tidal disruption events (TDEs), which occur when a star is destroyed by the gravitationalfield of a supermassive black hole, are unique probes into the properties of otherwise-quiescentsupermassive black holes (SMBHs). About 30 of them have been observed so far and this numberis steadily increasing, aided with surveys and new instruments coming online. Despite thiswealth of observational knowledge, our understanding of the TDE physics, which will ultimatelyallow us to interpret those observations, remains rudimentary at best. In particular, we stilldo not understand what causes the debris to lose its energy and angular momentum, fall intothe black hole and radiate. This project will make use of the fact that, at their core,TDEs are ultimately well-described by the general relativistic magnetohydrodynamics (GRMHD)equations of motion. By carrying out direct GRMHD simulations of TDEs, the project hopes to obtain a first-principlesunderstanding of TDE physics. The proposed simulations will provide answers to several long-standingquestions in the TDE community: How does the debris circularize, dissipate energy, and accreteonto the SMBH? What fraction of stellar gas forms the disk, what fraction is ejected as anoutflow, and how do these fractions depend on the black hole mass, spin, and the inclinationof the stellar orbit? Do eccentric accretion disks form and how does angular momentum transportwork in such disks? If such an eccentric disk is tilted, as is naturally expected in TDEs,does it undergo general relativistic precession? Do such disks produce relativistic jets andhow? Understanding these issues will allow the community to make meaningful, quantitativeinterpretation of TDE observations.Even though the project is focused on TDEs, it elucidates the basicphysics of tilted accretion disks and their jets that is applicable to a range of sourcesincluding quasars, black hole binaries, and ultra-luminous X-ray sources. Additionally, the proposed simulations will study, from first principlesand for the first time, the development of magnetorotational instability in eccentric tiltedaccretion disks and the long-term evolution and GR precession of such disks under continuousfeeding by the debris stream.Moreover, stars shredded by black holes and producing relativistic jets offer someof the most fascinating manifestations of general relativity. The project will disseminate theresults obtained as part of this proposal in public talks, summer schools, radio station andnewspaper interviews, and press releases. Finally, the project will involve undergraduate students in dataanalysis and visualization, and they will gain experience in working with Big Data, blackhole accretion and jet physics, presenting their results at conferences, and publishing theirwork in peer-reviewed journals.