2006AJ....131.2561C

The observed radial and transverse velocities of individual stars in the globular cluster M15 are used as inputs to a fully nonparametric code (CHASSIS) in order to estimate the equilibrium stellar distribution function and the three-dimensional mass density profile, from which are estimated the mass-to-light ratio, enclosed mass, and velocity dispersion profiles. In particular, the paper explores the possible existence of a central black hole in M15 via several runs that use the radial velocity data set, which offers kinematic measurements closer to the center of the cluster than the proper-motion data. These runs are distinguished from each other in the choice of the initial seed for the cluster characteristics; however, the profiles identified by the algorithm at the end of each run concur with each other within error bars, thus confirming the robustness of CHASSIS. The recovered density profiles are noted to exhibit unequivocal flattening interior to about 0.0525 pc. Also, the enclosed mass profile is very close to being a power-law function of radius <0.1 pc and is not horizontal. Simplistically speaking, these trends negate the possibility of the central mass being concentrated in a black hole, the lower bound on the radius of the sphere of influence of which would be ≳0.041 pc had it existed. However, proper analysis suggests that the mass enclosed within the inner 0.01 pc could be in the form of a black hole of mass ∼10³ M_☉under two different scenarios, which are discussed. The line-of-sight velocity dispersion is visually found to be very similar to the observed dispersion profile. The enclosed mass and velocity dispersion profiles calculated from runs done with the proper-motion data are found to be consistent with the profiles obtained with the radial velocity data.