The supermassive black hole at the center of our galaxy: Determination of its main physical parameters

We have used two astrometric methods developed at the Main Astronomical Observatory of the Russian Academy of Sciences—the method of apparent-motion parameters (AMP) and a direct geometrical method (DGM)—to derive the orbit of the star S2 around the Galactic center, and thereby the mass of the supermassive black hole at the Galactic center. The AMP method, which is based on measurements of the curvature of a fairly short orbital arc, is efficient if observational data on the relative radial velocity are available. The mass of the supermassive black hole was also estimated using astrophysical methods, based on the empirical relation between the masses of the supermassive black holes at the centers of galaxies and quasars and the radio and X-ray luminosities of these regions. We estimate the magnetic-field strength near the event horizon of the supermassive black hole at the Galactic center using a synchrotron self-absorption model.