Realistic Predictions for Gaia Black Hole Discoveries

Gaia astrometry has enabled the discovery of three dormant black holes (BHs) in wide binaries, challenging traditional binary evolution models. Numerous alternative formation models have been proposed, with several using simplified detectability metrics to forecast future detections. In this work, I applied a realistic forward-model of Gaia’s astrometric orbit catalog to synthetic BH binary populations from (a) isolated binary evolution (IBE, Chawla et al. 2022) and (b) dynamical formation in star clusters (Di Carlo et al. 2024). I found that the IBE model predicts that no BH binaries should have been detected in DR3, while the dynamical model overpredicts the observed number instead. I investigated the differences in assumptions between the population synthesis models that could have resulted in this discrepancy. Adopting the dynamical model and re-scaling to DR3, I predicted that approximately 30 BH binaries will be detected in Gaia DR4, representing about 0.1% of Milky Way BHs with luminous companions in au-scale orbits.

Read more about this research project in the associated publication here.