BHI Colloquium


Tuesday, October 27, 2020, 1:30pm to 2:30pm


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Sean Ressler (Astronomy) - UC Santa Barbara

Title: Arrested Development: Ab Initio Wind-Fed GRMHD Simulations of The Galactic Center

Abstract: The Galactic Center's Sagittarius A* (Sgr A*) needs no introduction.  The supermassive black hole is one of the primary targets of the Event Horizon Telescope and has also been the subject of decades-long, Nobel prize winning observational campaigns proving its existence and monitoring its activity.  This includes key work tracking the orbits of nearby stars, among which are the ~ 31 Wolf-Rayet (WR) stars with powerful stellar winds that feed the accretion flow.  All this information combines to make Sgr A* one of the best natural laboratories to study black hole accretion, which we often model using general relativistic magnetohydrodynamic (GRMHD) simulations.  Building on earlier work that simulated the interaction of the WR stellar winds on a relatively large scale (~10^5 Schwarschild radii), I will present a nested, three-simulation technique that expands the dynamical range of our calculation all the way to the event horizon.   As a result, the properties of our smallest scale GRMHD simulation are directly linked to the observationally constrained parameters of the WR stellar winds. We find that the horizon-scale accretion flow becomes magnetically arrested, a state well-studied in the literature in which the magnetic field builds up to the point that it is able to intermittently halt the inflow of gas.  This corroborates the conclusions of other recent works that forward model Sgr A* emission and find arrested models to be favored.  In this talk I will discuss these results and their implications in more detail.

Bio: Sean Ressler is a Kavli Institute for Theoretical Physics Fellow in theoretical astrophysics at UC Santa Barbara.  His work is focused on the underlying goal to form more predictive models of high energy astrophysical phenomena using both semi-analytic calculations and numerical simulations. 


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See also: Astronomy