The majority of stars are found in binary (or higher multiple) systems. Interactions between companion stars alter binary evolution. Many pieces of physics which determine how binariers form and evolve are currently uncertain; however, we have a variety of observations of different stages of binary evolution which can illuminate our understanding. The question is: how to translate observations to constraints on the physical processes that govern binaries? To solve this, we are developing Compact Object Mergers: Population Astrophysics and Statistics (COMPAS). COMPAS combines tools for statistical analysis and model selection with rapid population synthesis, allowing inferences to be made about the details of stellar and binary evolution.
COMPAS was initiated in order to explore the astrophysical implications of gravitational-wave observations. We are interested in understanding how the binary black holes discovered by LIGO could have formed, and how future observations could be best used to constrain our understanding of binary evolution. We are now including other observational signatures of binary evolution. Different observations provide different insights, and combining these leads to a more complete, concordance picture of binary astrophysics.