First Sagittarius A* Event Horizon Telescope Results: Variability, Morphology, and Black Hole Mass

In this talk I will describe the Event Horizon Telescope (EHT) modeling procedures, their application to the Sgr A* data, and our resulting quantification of the source variability, morphology, and black hole mass. We find that the Sgr A* data exhibit variability that exceeds what can be explained by the statistical and systematic uncertainties in the data or by the effects of interstellar scattering. The magnitude of this variability can be a substantial fraction of the correlated flux density, reaching up to 100% on some baselines. Through an exploration of simple geometric source models, we demonstrate that ring-like morphologies provide better fits to the EHT Sgr A* data than do other morphologies with comparable complexity. We develop two strategies for fitting static geometric ring models to the time-variable Sgr A* data; one strategy fits models only to short segments of data over which the source is static and averages these independent fits, while the other fits models to the full data set using a parametric model for the structural variability power spectrum around the average source structure. To bring the diameter measurements to a common physical scale, we calibrate the measurements from each method using a suite of synthetic data generated from general relativistic magnetohydrodynamic simulations of Sgr A*. This calibration constrains the angular size of the gravitational radius, which we combine with an independent distance measurement from maser parallaxes to determine the mass of Sgr A*.