Going Eccentric with Precessing Binaries

Future gravitational wave detectors, especially the Laser Interferometer Space Antenna (LISA), will be sensitive to black hole binaries formed in astrophysical environments that promote large eccentricities and spin precession. Gravitational wave models that include both effects have only recently been developed. One such model, the Efficient Fully Precessing Eccentric (EFPE) model, covers the inspiral stage with small-eccentricity-expanded amplitudes that are accurate for e < 0.3. New approaches are needed to model the inspiral for systems with larger eccentricities. In this work, we develop such a method, improving the leading-order gravitational wave amplitudes of the EFPE model so that they are accurate to e ≤ 0.8. Comparing the new amplitudes to the previous amplitudes in the LISA band, however, reveals that binaries with e₀ ≤ 0.5 at 4 years before merger circularize too quickly for there to be a significant difference between the two models. On the other hand, for e₀ > 0.5, the deviations are significant, particularly for binaries with total masses below 10⁵ solar masses. This suggests that the EFPE model may have a larger regime of validity in eccentricity space than previously thought, making it suitable for inspiral parameter estimation with LISA data, and reinforces the need for moderately eccentric amplitudes to faithfully characterize such binaries.