Introduction

This chapter deals with the kinematics and the dynamics of systems containing large-number (above 106) stars called globular clusters. It draws heavily on Chap. 10 of Vol. I and the basic ideas of stellar evolution described in the earlier chapters of this volume.

Globular clusters play an important role as systems in which many aspects of stellar-evolution theory can be directly tested and, in the process, can be used to provide significant information about the age and the mass function of stars in our galaxy. They also are examples of systems dominated by gravitational many-body interactions that hence undergo evolution in a manner quite different from other – simpler – systems. Finally, their dynamical evolution provides important points of similarity with central regions of galaxies, elliptical galaxies, and galaxy clusters. The kinematical aspects are discussed in the next section, and the rest of the chapter is devoted to dynamical issues.

Stellar Distribution and Ages of Globular Clusters

We have seen in the earlier chapters that the formation of stars from gaseous clouds is a fairly complex process that is not completely understood. Irrespective of the details, it seems reasonable to expect that, when stars form in a cloud, there will be a tendency for a large number of them to be close together, thereby forming a cluster of stars. Two broad categories of such star clusters have been seen in our galaxy, usually called open clusters and globular clusters.