Spatial and Binary Parameter Distributions of Black Hole Binaries in the Milky Way Detectable with Gaia

Abstract

Soon after Gaia Data Release 3 (DR3) in 2022 June, some candidates (and one confirmed) of detached black hole (BH)–luminous companion (LC) binaries have been reported. Existing and future detections of astrometric BH–LC binaries will shed light on the spatial distribution of these systems, which can deepen our understanding of the natal kicks and the underlying formation mechanism of BHs. By tracking Galactic orbits of BH–LC binaries obtained from BSE, we find that distributions of BH mass and the height from the Galactic plane ∣ z ∣ would help us give a constraint on the supernova model. We also indicate that the correlations of (i) orbital periods and eccentricities, and (ii) BH mass and ∣ z ∣ could be clues for the strength of the natal kick, and that the correlations of ( P , Z / Z _⊙ ) may give us a clue for the common-envelope (CE) efficiency. We also discuss the possibility of forming BH–LC binaries like the BH binary candidates reported in Gaia DR3 and Gaia BH 1, finding that if the candidates as well as the confirmed binary originate from isolated binaries, they favor models that produce low-mass BHs and have high CE efficiencies exceeding unity.

Keywords

• Astrometry
• Black holes
• Astrometric binary stars