THE EVOLUTION OF ACTIVE GALACTIC NUCLEI AND GLOBULAR CLUSTERS: MULTICOMPONENT MODELS

Abstract

The direct multimass FokkerPlanck method is used to follow the evolution of active galactic nuclei (AGN) and globular clusters. These objects are dense stellar systems in which gravitational interactions between individual stars are important. The stellar system contains stars with a realistic range of masses and a seed black hole at the center for AGN models. Stars lose mass or are depleted by three mechanisms: (1) tidal disruptions, (2) star-star collisions, and (3) stellar evolution. In order to model collisions realistically, I have extended the work of Spitzer and Saslaw (1966) on physical collisions to include stars of different masses and radii. I have found that collisions between nearly-identical stars produce the greatest fractional mass loss. In AGN models the ejected mass is followed by numerically integrating a set of steady-state-hydrodynamics equations. The resulting information determines the gas-flow profile near the black hole and the amount of matter falling into the black hole. From this the luminosity of the AGN and resulting black-hole mass can be determined. Collisions dominate the mass injection for high-density nuclei, and tidal disruptions and stellar evolution dominate in low-density nuclei. Resulting peak luminosities for AGN models vary from 1043 to 1048 erg s1 for initial central densities of 7 X 105 to 7 X 108 3Kq pc~3. Early in the simulations as much as 20% of the total system mass can be ejected from the AGN in the form of a supernova-driven wind. In all cases the final mass of the central black hole ranges from 10% to 90% of the initial system mass. In globular-cluster models the slope of the central surface brightness cusp that develops as a result of core collapse depends on the mass of the heaviest nonluminous remnants. The radius to which this cusp extends is greatly dependent on the number of nonluminous stars. For the globular cluster M 15, the stellar mass of the nonluminous remnant stars must be greater than 1.0 solar mass in order to fit observed surface brightness profiles.