A Fokker-Planck Study of Dense Rotating Stellar Clusters
  The dynamical evolution of dense stellar systems is simulated using a
two-dimensional Fokker-Planck method, with the goal of providing a model for
the formation of supermassive stars which could serve as seed objects for the
supermassive black holes of quasars. This work follows and expands on earlier
1-D studies of spherical clusters of main-sequence stars. The 2-D approach
allows for the study of rotating systems, as would be expected due to
cosmological tidal torquing; other physical effects included are collisional
mergers of stars and a bulk stellar bar perturbation in the gravitational
potential. The 3 Myr main-sequence lifetime for large stars provides an upper
limit on simulation times. Two general classes of initial systems are studied:
Plummer spheres, which represent stellar clusters, and \gamma=0 spheres, which
model galactic spheroids.
  At the initial densities of the modeled systems, mass segregation and runaway
stellar collisions alone are insufficient to induce core collapse within the
lifetime limit if no bar perturbation is included. However, core collapse is
not a requirement for the formation of a massive object: the choice of stellar
initial mass function is found to play a crucial role. When using an IMF
similar to that observed for dense stellar clusters the simulations show that
the stellar system forms massive (250M_\odot) objects by collisional mergers;
in almost all such cases the presence of a stellar bar allows for sufficient
additional outward transport of angular momentum that a core-collapse state is
reached with corresponding further increase in the rate of formation of massive
objects. In contrast, simulations using an IMF similar to that observed for
field stars in general (which is weighted more towards lower masses) produce no
massive objects, and reach core collapse only for initial models which
represent the highest-density galactic spheriods.
