GPU-Enabled General Relativistic Simulations of Misaligned Black Hole Accretion Systems

Alexander Tchekhovskoy, Northwestern University

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Alexander Tchekhovskoy, Philipp Moesta, Monika Moscibrodzka, David Radice, Matthew Liska, Manichandra Morampudi, Casper Hesp, Ziri Younsi, Koushik Chatterjee, Eric Coughlin, Kyle Kremer, David van Eijnatten, Ian Christie, Zachary Andalman, Marc van Iersel, Danat Issa, DooSoo Yoon, Lev Barash, Emma Kaufman, Vikram Manikantan, Nicholas Omahen, Gabriel Casabona, Aretaios Lalakos, Beverly Lowell

Tidal disruption events (TDEs), which occur when a star is destroyed by the gravitational field of a supermassive black hole, are unique probes into the properties of otherwise-quiescent supermassive black holes (SMBHs). About 30 of them have been observed so far and this number is steadily increasing, aided with surveys and new instruments coming online. Despite this wealth of observational knowledge, our understanding of the TDE physics, which will ultimately allow us to interpret those observations, remains rudimentary at best. In particular, we still do not understand what causes the debris to lose its energy and angular momentum, fall into the 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-principles understanding of TDE physics.

The proposed simulations will provide answers to several long-standing questions in the TDE community: How does the debris circularize, dissipate energy, and accrete onto the SMBH? What fraction of stellar gas forms the disk, what fraction is ejected as an outflow, and how do these fractions depend on the black hole mass, spin, and the inclination of the stellar orbit? Do eccentric accretion disks form and how does angular momentum transport work 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 and how? Understanding these issues will allow the community to make meaningful, quantitative interpretation of TDE observations.

Even though the project is focused on TDEs, it elucidates the basic physics of tilted accretion disks and their jets that is applicable to a range of sources including quasars, black hole binaries, and ultra-luminous X-ray sources.

Additionally, the proposed simulations will study, from first principles and for the first time, the development of magnetorotational instability in eccentric tilted accretion disks and the long-term evolution and GR precession of such disks under continuous feeding by the debris stream.

Moreover, stars shredded by black holes and producing relativistic jets offer some of the most fascinating manifestations of general relativity. The project will disseminate the results obtained as part of this proposal in public talks, summer schools, radio station and newspaper interviews, and press releases. Finally, the project will involve undergraduate students in data analysis and visualization, and they will gain experience in working with Big Data, black hole accretion and jet physics, presenting their results at conferences, and publishing their work in peer-reviewed journals.