A Nonparametric Estimate of the Mass of the Central Black Hole in the Galaxy

Abstract

We estimate the mass of the central black hole in our Galaxy from stellar kinematic data published by Ghez et al. and Genzel et al. For this we develop a method, related to that presented by Merritt in 1993, for nonparametrically reconstructing the mass profile and the stellar distribution function in the central region of the Galaxy from discrete kinematic data, including velocity errors. Models are searched using the Metropolis algorithm. We assume that the mass distribution is spherical and the stellar velocity distribution is isotropic, and we devise a test of this assumption. From proper motions we obtain an enclosed mass of (2.0+/-0.7)×106 Msolar within the inner 0.0044 pc, from radial velocities we obtain a mass of 2.2+1.6-1.0×106 Msolar within 0.046 pc, and from three-dimensional velocities we obtain 1.8+0.4-0.3×106 Msolar within 0.046 pc.