Remnant mass and spin relations for eccentric binary black hole mergers.

Merging binary black holes produce a remnant black hole with new properties that are encoded in the emitted gravitational waves. Numerical relativity simulations and semi-analytic methods have led to the development of fitting functions that predict the remnant black hole's final mass and final spin, given the initial binary mass ratio and component spins. Understanding the mapping between the initial binary parameters and the remnant parameters is important for modeling gravitational-wave templates and performing tests of General Relativity (GR). While black hole binaries tend to circularize during the inspiral phase, their orbits may still have a nonnegligible eccentricity just before the merger phase. Current fitting functions do not account for orbital eccentricity, and neglecting this could impact tests of GR or precision waveform modeling. Here we develop a semi-analytic method to include eccentricity in the final mass and final spin relations. Our scheme is based on energy and angular momentum conservation arguments. Corrections to the circular limit on the final mass and spin are of order a few percent if the eccentricity at the last-stable-orbit exceeds ~0.5.