On the evolution of globular cluster systems. I - Present characteristics and rate of destruction in our Galaxy

The authors model the current dynamical state and rate of destruction for the system of globular clusters in our Galaxy. Starting from the observed positions and radial velocities of 83 globular clusters, the authors complement them with an assumed kinematical model for the globular cluster system to provide the two unmeasured transverse velocities. The authors then integrate the orbits generated by these initial conditions using two different galactic mass models. Rates of destruction are calculated for the physical processes: evaporation through two-body relaxation, dynamical friction, and gravitational shocks in passages through the galactic disk as well as in perigalacticon passages near the galactic bulge. It is found that gravitational shocks due to the central bulge of the Galaxy are very efficient in destroying clusters on highly radial orbits. At the Sun's galactic radius, evaporation is the most important mechanism, followed by disk shocking and dynamical friction. The authors estimate that the current death rate is 0.5 clusters per billion years.