Tidal disruption events, in which a star is partially or completely disrupted by the tidal gravitational field of a supermassive black hole, can lead to transient infall of matter toward the black…

This federal contract award is to The Regents of the University of Colorado, doing business as the University of Colorado Office of Contracts and Grants Division, for $595,174.93 to conduct research on tidal disruption events. Tidal disruption events occur when a star is partially or completely disrupted by the gravitational field of a supermassive black hole, leading to the transient infall of matter toward the black hole. The research will use magnetohydrodynamic simulations to study the early evolution of these events, determine if large-scale magnetic fields can drive powerful jets, and model the physics of the transition between thick and thin accretion flows as infall subsides. This research supports NASA's X-ray and ultraviolet observations as well as ground-based detection efforts, addressing fundamental questions about high-energy phenomena in the universe. The award is a grant for research and does not have a set-aside designation.

Tidal disruption events, in which a star is partially or completely disrupted by the tidal gravitational field of a supermassive black hole, can lead to transient infall of matter toward the black hole at a rate that far exceeds the eddington limit. Of the two dozen or so candidate events that have been detected, two show evidence of energy being liberated at a highly super-eddington rate, including powerful x-RAY emitting jets. As surveys discover many more events in the near future, tidal disruption events will become a prime probe of accretion physics and stellar dynamics in galactic nuclei. We propose an analytic and computational study of the initial conditions of tidal disruption events, their accretion signatures, and their long-term evolution. We will: (1) use magnetohydrodynamic simulations to study the early evolution of tidal disruption events when the fallback rate is super- eddington. We will study the initial circularization and heating of the debris due to shocks and pressure forces, the amplification of the magnetic field by shear, the subsequent accretion driven by magnetic forces, and the further expansion of the debris into a weakly bound, quasi-spherical envelope that continues to accrete at a super-eddington rate. (2) determine whether large-scale magnetic fields can build up quickly enough within the accreting envelope that forms after a disruption to drive powerful jets, or whether the jets are accelerated by radiation forces. (3) model the physics of the transition between geometrically thick and thin accretion flows as infall subsides at late times following a disruption, and investigate whether such a transition could be studied observationally in a subset of tidal disruption events. The study of tidal disruption events is a multi-wavelength endeavor, involving nasas x-RAY and ultraviolet observatories as well as ground-based detectors. These events represent controlled experiments in black hole accretion, which challenge established ideas about how fast black hole can grow and how they produce jets. The proposed study thus addresses fundamental questions about the highest energy phenomena in the universe.