Dynamical Effects of Successive Mergers on the Evolution of Spherical Stellar Systems

The dynamical effects of high-mass stars formed out of successive mergers among tidally captured binaries on the evolution of spherical stellar systems are investigated. It is assumed that all tidally captured systems become mergers. Stellar evolution is simulated by computing the mean age of the mass group and applying a specific death rate, as a function of mean age. Successive mergers and stellar evolution are efficient for reversing core-collapse in clusters with large N. For stellar systems with N = 10^5-6, three-body binary heating among high-mass stars provides significant energy to drive the bounce and postcollapse expansion. For small N, three-body binaries among light stars provide most of the energy to drive the postcollapse expansion. Stellar systems with very large N (⪆10⁷) are vulnerable to the "merger instability," which may lead to the formation of a central black hole.