An Inverse Look at the Center of M15
  The observed radial and transverse velocities of individual stars in M15 are implemented as inputs to a fully non-parametric code (CHASSIS) in order to estimate the equilibrium stellar distribution function and the three-dimensional mass density profile. In particular, the paper explores the possibility of the existence of a central black hole in M15 via several runs that utilize the radial velocity data set which offers kinematic measurements closer to the centre 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, inner to about 0.0525pc. Also, the enclosed mass profile is very close to being a power-law function of radius inside 0.1pc and is not horizontal. Simplistically speaking, these trends negate the possibility of the central mass to be concentrated in a black hole, the lower bound on the radius of the sphere of influence of which would be $\gtrsim$0.041pc, had it existed. However, proper analysis suggests that the mass enclosed within the inner 0.01pc could be in the form of a black hole of mass $\sim{10^3}$M$_{\odot}$, 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. 
Dalia Chakrabarty