Nonlinear gravitational-wave memory from binary black hole mergers

TL;DR

This paper calculates the nonlinear Christodoulou gravitational-wave memory from binary black hole mergers across all phases using advanced models, highlighting its potential observability with space-based detectors like LISA.

Contribution

It provides the first comprehensive computation of the nonlinear memory including inspiral, merger, and ringdown phases using EOB and analytic models.

Findings

Memory is detectable in supermassive black hole mergers with LISA.

Nonlinear memory contributes a nonoscillatory component to gravitational waves.

Detection could test gravity's ability to 'gravitate.'

Abstract

Some astrophysical sources of gravitational waves can produce a "memory effect," which causes a permanent displacement of the test masses in a freely falling gravitational-wave detector. The Christodoulou memory is a particularly interesting nonlinear form of memory that arises from the gravitational-wave stress-energy tensor's contribution to the distant gravitational-wave field. This nonlinear memory contributes a nonoscillatory component to the gravitational-wave signal at leading (Newtonian-quadrupole) order in the waveform amplitude. Previous computations of the memory and its detectability considered only the inspiral phase of binary black hole coalescence. Using an "effective-one-body" (EOB) approach calibrated to numerical relativity simulations, as well as a simple fully analytic model, the Christodoulou memory is computed for the inspiral, merger, and ringdown. The memory will be very difficult to detect with ground-based interferometers, but is likely to be observable in supermassive black hole mergers with LISA out to a redshift of two. Detection of the nonlinear memory could serve as an experimental test of the ability of gravity to "gravitate."