Late-time tails in eccentric binary black hole coalescence waveforms

Black hole binaries with small mass ratios will be critical targets for the forthcoming Laser Interferometer Space Antenna (LISA) mission. The small-mass-ratio limit also provides useful tools for studying the dynamics of compact binary systems and the gravitational waves they emit. Using an eccentric Ori-Thorne procedure, we build worldlines that describe the full inspiral and plunge of a small body on an initially eccentric orbit of a Kerr black hole. We then calculate the gravitational waves associated with these trajectories with a code that solves the Teukolsky equation in the time domain. The late-time ringdown from such a waveform exhibits tail behavior that can be well-modeled as a decaying power law. In this work, we examine the impact of orbital eccentricity and its associated phase parameter, the radial anomaly angle, on the excitation of the power-law tail. We find that these tails are amplified by eccentricity, dominating the ringdown earlier and with higher amplitudes than in circular mergers. However, the detailed morphology of the tail is particularly sensitive to the trajectory's initial value of the radial anomaly angle, limiting the universality of the eccentric ringdown. While it is still unclear if the tail contribution to the ringdown will be detectable by future gravitational wave experiments, a more detailed understanding of the late-time waveform provides key insight into the ringdown and its dependence on a binary's coalescence geometry.