Stellar encounters in dense clusters

• Main Author: Bailey, V. C.
• Published: University of Cambridge 2000
• Subjects: 520
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596260

This thesis is concerned with the role of stellar encounters and collisions in dense clusters. In Chapter 1 I discuss basic collision cross sections and rates, and briefly discuss the cluster cores in which they occur. A short discussion of the history of stellar-collision calculations is then given, followed by an overview of the stellar exotica that may be produced in collisions between stars. In Chapter 2 stellar collisions involving luminous red-giant stars are investigated. Recent observations of the central parsec of the Galaxy reveal that highly-luminous giants are missing from the innermost 0.1 <I>pc</I>. The Galactic core contains a very dense stellar cluster, which suggests that the giants may have been destroyed in stellar collisions. Collision rates are calculated for such giants, and simulations between large red giants and other single stars are performed. In Chapter 3 the role of the stellar collisions in the formation of stars of masses > 10M⊙ is examined. Accretion of ambient gas by stars in young cluster cores give rise to multiple stellar collisions to occur. Mergers between the stars is expected to build up stars of masses > 10M⊙. This may provide a solution to the problem of massive-star formation, in which the radiation pressure of stellar cores of masses < 10M⊙ is sufficiently high to halt the infall of gas onto the core, thereby limiting the stellar mass. Simulations of distant encounters and physical collisions between young stars are performed in order to compute tidal-capture radii and the nature of merged objects. The findings are then used to recompute massive-star formation time-scales. In Chapter 4 collision rates involving binary stars are calculated. Stellar evolution models are analysed to examine which stellar species are most likely to undergo collisions. Simulations of encounter and collisions are then performed in order to compute tidal-capture radii, mass loss and merger radii between stars of various masses and for stars at various stages of evolution. The data produced is intended for use in simulations of stellar cluster evolution by N-body codes in which stellar evolution and close stellar encounters are included.