What the Event Horizon Telescope Reveals on Physics of the Accretion Flow Around Sgr A* and M 87*

We compare EHT images of SgrA* and M87* as well as non-EHT data spanning from the radio to the X-ray to a broad suite of theoretical GRMHD simulations. These simulations span a large parameter space and explore a variety of assumptions about the accretion flow, including aligned and tilted models, thermal and non-thermal electron heating prescriptions, and wind-fed models. For SgrA*, all of the models fail to match one or more of the observational constraints, with the lightcurve and structural variability in particular eliminating nearly all models. For M87*, measurements of the resolved linear polarization constrain the magnetic field structure close to the event horizon. In both cases, observational constraints favor models with strong, dynamically important magnetic fields.