The gravitational-wave memory effect

TL;DR

This paper reviews the nonlinear gravitational-wave memory effect, its theoretical calculations across all phases of black hole mergers, and assesses its potential detectability with future space-based detectors like LISA.

Contribution

It provides the first comprehensive calculations of nonlinear memory throughout the entire binary black hole coalescence process and estimates its observability.

Findings

Memory contribution computed to third post-Newtonian order.

First calculations including all phases of binary black hole coalescence.

Realistic estimates of LISA's ability to detect the memory.

Abstract

The nonlinear memory effect is a slowly-growing, non-oscillatory contribution to the gravitational-wave amplitude. It originates from gravitational waves that are sourced by the previously emitted waves. In an ideal gravitational-wave interferometer a gravitational-wave with memory causes a permanent displacement of the test masses that persists after the wave has passed. Surprisingly, the nonlinear memory affects the signal amplitude starting at leading (Newtonian-quadrupole) order. Despite this fact, the nonlinear memory is not easily extracted from current numerical relativity simulations. After reviewing the linear and nonlinear memory I summarize some recent work, including: (1) computations of the memory contribution to the inspiral waveform amplitude (thus completing the waveform to third post-Newtonian order); (2) the first calculations of the nonlinear memory that include all phases of binary black hole coalescence (inspiral, merger, ringdown); and (3) realistic estimates of the detectability of the memory with LISA.