Phenomenology and origin of late-time tails in eccentric binary black hole mergers

TL;DR

This paper studies the late-time gravitational wave tails in eccentric binary black hole mergers, revealing their dependence on eccentricity and spin, and providing a theoretical and numerical understanding of their origin.

Contribution

It introduces a detailed phenomenological analysis of late-time tails in eccentric BBH mergers, including their power-law behavior and origin, supported by numerical experiments and a publicly available analysis framework.

Findings

Tails become more prominent with increasing eccentricity.

The tail decay follows a power law close to exponent -4.

Tails are excited when the smaller black hole is near apocenter.

Abstract

We investigate the late-time tail behavior in gravitational waves from merging eccentric binary black holes (BBH) using black hole perturbation theory. For simplicity, we focus only on the dominant quadrupolar mode of the radiation. We demonstrate that such tails become more prominent as eccentricity increases. Exploring the phenomenology of the tails in both spinning and non-spinning eccentric binaries, with the spin magnitude varying from $\chi=-0.6$ to $\chi=+0.6$ and eccentricity as high as $e=0.98$, we find that these tails can be well approximated by a slowly decaying power law. We study the power law for varying systems and find that the power law exponent lies close to the theoretically expected value $-4$. Finally, using both plunge geodesic and radiation-reaction-driven orbits, we perform a series of numerical experiments to understand the origin of the tails in BBH simulations. Our results suggest that the late-time tails are strongly excited in eccentric BBH systems when the smaller black hole is in the neighborhood of the apocenter, as opposed to any structure in the strong field of the larger black hole. Our analysis framework is publicly available through the \texttt{gwtails} Python package.