Astrometric Detection of Ultralight Dark Matter

TL;DR

This paper proposes using astrometry to detect ultralight dark matter by observing its gravitational effects on the apparent positions of distant astrophysical objects, potentially revealing dark matter with extremely low masses.

Contribution

It introduces a novel astrometric method for detecting ultralight dark matter through metric perturbations and analyzes the sensitivity of current and future surveys.

Findings

Current astrometric surveys can detect dark matter with masses as low as 10^{-33} eV.

Detection is feasible for local dark matter velocities around 10^{-3}.

Energy density detection threshold is approximately 10^{-4} GeV/cm^3.

Abstract

Ultralight dark matter induces time-dependent perturbations in the spacetime metric, enabling its gravitational direct detection. In this work, we propose using astrometry to detect dark matter. After reviewing the calculation of the metric in the presence of scalar dark matter, we study the influence of the perturbations on the apparent motion of astrophysical bodies. We apply our results to angular position measurements of quasars, whose vast distances from Earth present an opportunity to discover dark matter with a mass as low as $10^{-33} \, \mathrm{eV} $. We explore the prospects of very long baseline interferometry and optical astrometric survey measurements for detecting ultralight relics, finding that for the smallest masses, current astrometric surveys can detect dark matter moving locally with a velocity of $10^{-3}$ with energy density as low as $10 ^{ - 4} ~{\rm GeV} / {\rm cm} ^3 $.