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

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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.