Gaia may detect hundreds of black holes

Discoveries of stellar-mass black holes (BHs) via X-ray, radio, and gravitational waves, combined with binary stellar evolution theory indicate that BHs with detached luminous companions (LCs) should be found in large numbers in the Milky Way (MW). We simulate highly realistic models of BH--LC binaries in the MW using a publicly available binary-population synthesis code COSMIC. We find that Gaia can discover a hundred to a few hundreds of detached BH--LC binaries by monitoring the motions of the LCs during its 10 year observation baseline. Proper motion, parallax, and magnitude of the LCs would also be known from Gaia data, hence, LC properties, such as mass, luminosity, age, and metallicity can be determined relatively easily. Follow-up radial velocity observations to better constrain the BH mass and BH--LC properties are also possible for a majority of these candidates. If found, these BHs will be the first where their mass as well as the metallicity and age of their progenitors will be known almost model-independently. A null result will also provide strong constraints on initial binary properties of high-mass stars and supernova physics. In my talk, I will share our exciting key results.