Gaia's promise to detect compact-object binaries: where we stand with the third data release (2508.21805v1)

Abstract: With its third data release (DR3), Gaia begins unveiling dormant candidate compact object (CO) binaries with luminous companion (LC) as predicted by several past theoretical studies. To date, 3 black hole (BH), 21 neutron star (NS), and ~3200 white dwarf (WD) candidates have been identified with LCs in detached orbits using astrometry. We adopt an observationally motivated sampling scheme for the star formation history of the Milky Way, and initial zero-age main-sequence binary properties, incorporate all relevant binary interaction processes during evolution to obtain a realistic present-day intrinsic population of CO--LC binaries. We apply Gaia's selection criteria to identify the CO--LC binaries detectable using the observational cuts applicable for DR3 as well as its end-of-mission (EOM). We find that under the DR3 selection cuts, our detectable population includes no BH--LCs, approximately 10-40 NS--LCs, and around ~4300 WD--LCs. In contrast, by EOM, the expected numbers increase to 30-300 BH--LCs, 1500-5000 NS--LCs, and ~10^5-10^6 WD--LC binaries, primarily because of the significantly longer baseline of observation.