Ultra-Light Dark Matter Resonates with Binary Pulsars

TL;DR

This paper explores how ultra-light dark matter can influence binary pulsar orbits through resonant effects, proposing pulsars as sensitive probes to detect or constrain such dark matter interactions, with future observatories promising improved sensitivity.

Contribution

It introduces the idea that binary pulsars can be used to detect resonant effects of ultra-light dark matter and provides estimates of current and future observational sensitivities.

Findings

Current observations constrain direct coupling of dark matter to matter.

Resonant effects can secularly alter binary pulsar orbital periods.

Upcoming radio telescopes will significantly improve detection sensitivity.

Abstract

We consider the scenario where dark matter (DM) is represented by an ultra-light classical scalar field performing coherent periodic oscillations. We point out that such DM perturbs the dynamics of binary systems either through its gravitational field or via direct coupling to ordinary matter. This perturbation gets resonantly amplified if the frequency of DM oscillations is close to a (half-)integer multiple of the orbital frequency of the system and leads to a secular variation of the orbital period. We suggest to use binary pulsars as probes of this scenario and estimate their sensitivity. While the current accuracy of observations is not yet sufficient to probe the purely gravitational effect of DM, it already yields constraints on direct coupling that are competitive with other bounds. The sensitivity will increase with the upcoming radio observatories such as Square Kilometer Array.