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Towards More Predictive Models of Galactic Center Accretion


Sagittarius A* (Sgr A*), the roughly 4 million solar mass black hole at the center of our galaxy, is arguably the best natural test-bed for supermassive black hole accretion models. Its close proximity allows for detailed observations to be made across the electromagnetic spectrum that provide strong, multi-scale constraints on analytic and numerical calculations. These include exciting new event horizon scale results that directly probe the strong field regime for the first time. Spanning roughly 7 orders of magnitude in radius, the accretion system begins at ~ parsec scales where a large population of Wolf-Rayet (WR) stars interact via powerful stellar winds. A fraction of the wind material accretes to the event horizon scales, heating up and radiating on the way down to provide the observed multi-wavelength emission. Detailed modeling of this process requires 3D numerical simulations spanning as large of a dynamical range as possible. The goal of this thesis has been to improve the predictive power of such simulations applied to Sgr A* by limiting the number of free parameters that they contain. This is done by incorporating more theoretical and observational knowledge into the calculations, for example, what collisionless physics tells us about how electrons/ions are heated in a turbulent medium and the properties of the winds of the WR stars. The resulting simulations have shown excellent agreement with a wide range of observational constraints and could have major implications for how the accretion flow around Sgr A* is modeled in the future. The techniques presented here are also applicable to other low luminosity AGN and X-ray binaries.

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