Weighing the Darkness. II. Astrometric Measurement of Partial Orbits with Gaia

Abstract Over the course of several years, stars trace helical trajectories as they traverse across sky due to combined effects proper motion and parallax. It is well known that gravitational pull an unseen companion can cause deviations these tracks. Several studies have pointed out astrometric mission Gaia will be able identify a slew new exoplanets, stellar binaries, compact object companions with orbital periods short tens days long Gaia's lifetime. Here, we use mock observations demonstrate characterize black hole luminous longer than Such binaries too exhibit complete orbits, instead are identified through curvature in their characteristic paths. By simultaneously measuring radius this velocity, constraints placed on underlying orbit. We quantify precision which measure accelerations apply model predictions for population holes orbiting neighborhood. Although degeneracies imply many induced by hidden could also explained faint low-mass stars, discuss how nature certain putative confirmed high confidence using data alone.