Persistent Astrometric Deflections from Gravitational-Wave Memory

TL;DR

This paper explores how gravitational-wave memory causes permanent, distinctive astrometric deflections in star positions, which could impact cosmological observations and offer new insights into gravitational wave phenomena.

Contribution

It characterizes the unique astrometric signatures of gravitational-wave memory and discusses their potential observational implications, distinguishing them from oscillatory gravitational waves.

Findings

Memory-induced deflections are permanent and qualitatively distinct from oscillatory GWs.

These deflections can develop as a random walk over cosmological timescales.

Implications for cosmic microwave background observations are discussed.

Abstract

Gravitational waves (GWs) produce small distortions in the observable distribution of stars in the sky. We describe the characteristic pattern of astrometric deflections created by a specific gravitational waveform called a burst with memory. Memory is a permanent, residual distortion of space left in the wake of GWs. We demonstrate that the astrometric effects of GW memory are qualitatively distinct from those of more broadly considered, oscillatory GWs---distinct in ways with potentially far-reaching observational implications. We discuss some such implications pertaining to the random-walk development of memory-induced deflection signatures over cosmological time spans and how those may influence observations of the cosmic microwave background.