Tracing the evolution of eccentric precessing binary black holes: A hybrid approach

To make astrophysical statements, it is important to evolve a generic binary black hole between formation and coalescence. There exist codes to do this for quasi-circular precessing binaries, but not yet any for eccentric precessing binaries. Evolving a binary back in time lets us obtain its properties at formation. Evolving it forward in time using its properties at formation and feeding our predictions to numerical relativity fits lets us predict the merger remnant’s properties (though these fits are currently only available for precessing binaries with negligible eccentricities near the merger). In this project, we develop a code for the hybrid evolution of an eccentric precessing binary black hole. Here, we evolve the binary using equations averaged over an orbital period close to the merger and transition to equations averaged over a precessional period for better computational efficiency when the binary has a large separation. We empirically determine the transition frequency between the two types of evolution to obtain a given accuracy. Applying this code, we study how the parameters of eccentric binaries near merger are mapped to their spin tilts at large separations, which are useful parameters for studying the formation channels of binary black holes.