Binary Systems as Resonance Detectors for Gravitational Waves

TL;DR

This paper proposes using binary systems, like pulsars, as resonance detectors for gravitational waves, establishing new bounds on the gravitational-wave background at specific frequencies through long-term orbital monitoring.

Contribution

It introduces a novel method of constraining gravitational waves by analyzing orbital variations in binary systems over decades, complementing existing detection techniques.

Findings

Bound on gravitational-wave strain amplitude h_c < 7.9×10^(-14) at ~10^(-4) Hz

Constraint can improve to ~3.8×10^(-15) with future observations

Method applicable to other binaries, including Earth-Moon system

Abstract

Gravitational waves at suitable frequencies can resonantly interact with a binary system, inducing changes to its orbit. A stochastic gravitational-wave background causes the orbital elements of the binary to execute a classic random walk, with the variance of orbital elements growing with time. The lack of such a random walk in binaries that have been monitored with high precision over long time-scales can thus be used to place an upper bound on the gravitational-wave background. Using periastron time data from the Hulse-Taylor binary pulsar spanning ~30 years, we obtain a bound of h_c < 7.9*10^(-14) at ~10^(-4) Hz, where h_c is the strain amplitude per logarithmic frequency interval. Our constraint complements those from pulsar timing arrays, which probe much lower frequencies, and ground-based gravitational-wave observations, which probe much higher frequencies. Interesting sources in our frequency band, which overlaps the lower sensitive frequencies of proposed space-based observatories, include white-dwarf/supermassive black-hole binaries in the early/late stages of inspiral, and TeV scale preheating or phase transitions. The bound improves as (time span)^(-2) and (sampling rate)^(-1/2). The Hulse-Taylor constraint can be improved to ~3.8*10^(-15) with a suitable observational campaign over the next decade. Our approach can also be applied to other binaries, including (with suitable care) the Earth-Moon system, to obtain constraints at different frequencies. The observation of additional binary pulsars with the SKA could reach a sensitivity of h_c ~ 3*10^(-17).