Binary pulsars as dark-matter probes

TL;DR

Binary pulsar observations can be used to detect or constrain dark matter density through its dynamical effects on orbital motion, with current and future measurements providing increasingly stringent bounds.

Contribution

This paper introduces a method to use binary pulsar timing to place model-independent bounds on dark-matter density in different galactic regions.

Findings

Timing of pulsar J1713+0747 constrains dark matter density to less than 10^5 GeV/cm^3 at 7 kpc.

Detection of pulsars within 10 pc could tightly constrain dark matter halo profiles.

Square Kilometer Array can improve bounds on local dark matter density by two orders of magnitude.

Abstract

During the motion of a binary pulsar around the Galactic center, the pulsar and its companion experience a wind of dark-matter particles that can affect the orbital motion through dynamical friction. We show that this effect produces a characteristic seasonal modulation of the orbit and causes a secular change of the orbital period whose magnitude can be well within the astonishing precision of various binary-pulsar observations. Our analysis is valid for binary systems with orbital period longer than a day. By comparing this effect with pulsar-timing measurements, it is possible to derive model-independent upper bounds on the dark-matter density at different distances $D$ from the Galactic center. For example, the precision timing of J1713+0747 imposes $\rho_{\rm DM}\lesssim 10^5\,{\rm GeV/cm}^3$ at $D\approx7\,{\rm kpc}$. The detection of a binary pulsar at $D\lesssim 10\,{\rm pc}$ could provide stringent constraints on dark-matter halo profiles and on growth models of the central black hole. The Square Kilometer Array can improve current bounds by 2 orders of magnitude, potentially constraining the local density of dark matter to unprecedented levels.