The Astronomical Multipurpose Software Environment and the Ecology of Star Clusters

Star cluster ecology is the field of research where stellar evolution, gravitational dynamics, hydrodynamcs and the background potential dynamics of the parent galaxy interact to a complex non-linear evolution of self gravitating stellar systems. I will review the processes related to the ecology of stellar clusters, discuss the numerical hurdles and the physical principles. In addition, I will introduce the AMUSE framework with which we are performing simulations of the ecology of stellar clusters. AMUSE is a general purpose framework for interconnecting existing scientific software with a homogeneous and unified interface. Since the framework is based on the standard message passing interface, any production ready code that is written in a language that supports its native bindings can be incorporated; in addition, our framework is intrinsically parallel and it conveniently separates all the numerical solvers in memory. The strict separation also enables the possibility to realize unit conversion between the different modules and to recover from fatalities in a unified and structured way. The time spent in the framework is relatively small, and for production simulations we measured an overhead of at most 10%, which in our case is acceptable. Due to the unified structure of the interface, incorporating new modules which address the same physics is relatively straightforward. The time stepping between the codes can be simply consecutive or realized via a mixed variable symplectic method in which the Hamiltonian of the problem is solved in separate steps and combined via a Verlet-leapfrog integration scheme. In our experience with an implementation for multiphysics simulations in astrophysics, we encounter relatively few problems with the strict separation in methods, and the results of our test simulations are consistent with earlier results that use a monolithic framework.