Gravitational-wave memory revisited: memory from the merger and recoil of binary black holes

TL;DR

This paper revisits gravitational-wave memory from binary black hole mergers, modeling its evolution through inspiral, merger, and ringdown phases, and assesses the detectability of these effects with future gravitational-wave observatories like LISA.

Contribution

It introduces an effective-one-body model calibrated with numerical relativity to accurately predict the memory's evolution and final saturation, including recoil effects, across all phases of binary coalescence.

Findings

Memory effects are significant for supermassive black hole mergers detectable by LISA.

The model predicts the amplitude and evolution of the Christodoulou memory during all phases.

Recoil-induced effects like linear memory and Doppler shifts could be observable.

Abstract

Gravitational-wave memory refers to the permanent displacement of the test masses in an idealized (freely-falling) gravitational-wave interferometer. Inspiraling binaries produce a particularly interesting form of memory--the Christodoulou memory. Although it originates from nonlinear interactions at 2.5 post-Newtonian order, the Christodoulou memory affects the gravitational-wave amplitude at leading (Newtonian) order. Previous calculations have computed this non-oscillatory amplitude correction during the inspiral phase of binary coalescence. Using an "effective-one-body" description calibrated with the results of numerical relativity simulations, the evolution of the memory during the inspiral, merger, and ringdown phases, as well as the memory's final saturation value, are calculated. Using this model for the memory, the prospects for its detection are examined, particularly for supermassive black hole binary coalescences that LISA will detect with high signal-to-noise ratios. Coalescing binary black holes also experience center-of-mass recoil due to the anisotropic emission of gravitational radiation. These recoils can manifest themselves in the gravitational-wave signal in the form of a "linear" memory and a Doppler shift of the quasi-normal-mode frequencies. The prospects for observing these effects are also discussed.