The Starlab Environment for Dense Stellar Systems

Traditionally, a simulation of a dense stellar system required choosing an initial model, running an integrator, and analyzing the output. Almost all of the effort went into writing a clever integrator that could handle binaries, triples and encounters between various multiple systems efficiently. Recently, the scope and complexity of these simulations has increased dramatically, for three reasons: 1) the sheer size of the data sets, measured in Terabytes, make traditional 'awking and grepping' of a single output file impractical; 2) the addition of stellar evolution data brings qualitatively new challenges to the data reduction; 3) increased realism of the simulations invites realistic forms of 'SOS': Simulations of Observations of Simulations, to be compared directly with observations. We are now witnessing a shift toward the construction of archives as well as tailored forms of visualization including the use of virtual reality simulators and planetarium domes, and a coupling of both with budding efforts in constructing virtual observatories. This review describes these new trends, presenting Starlab as the first example of a full software environment for realistic large-scale simulations of dense stellar systems. Modeling a star cluster on a computer is a subject with a published history of more than forty years, starting with the 10-body simulations by von Hoerner (1960). These pioneering calculations had to be halted when the first binary was formed. In those days neither was the hardware fast enough, nor the software sophisticated enough to follow the long-term evolution of a perturbed binary. Rapid improvement of both hardware and software allowed the treatment of dynamically formed binaries by the mid-sixties, but the maximum number of bodies remained in the regime N < 100 where relaxation effects could not be ignored on a crossing time. By the early seventies, larger systems could be modeled, up to N = 500. By that time a clear separation between relaxation time and crossing time could be observed. These simulations showed that the core of a typical star cluster contracts as a result of heat flowing toward its outer regions, on a two-body relaxation time scale. This phenomenon had been predicted theoretically and was dubbed 'gravothermal collapse' or 'core collapse', where the term 'collapse' is perhaps a bit misleading since the process takes billions of years for a typical globular cluster. It was observed in the simulations that this type of collapse continues 1