Detecting Black Hole Binaries by Gaia

We study the prospects of the Gaia satellite to identify black hole (BH) binary systems by detecting the orbital motion of the companion stars. Taking into account the initial mass function, mass transfer, common envelope phase, interstellar absorption, and identifiability of the systems, we estimate the number of BH binaries that can be detected by Gaia and their distributions with respect to the BH mass. Considering several models with different parameters, we find that ∼200-1000 BH binaries could be detected by Gaia during its ∼5 years operation. The shape of the BH mass distribution function is affected strongly by the zero-age main sequence (ZAMS) stellar mass-BH mass relation. We show that once this distribution is established observationally, we will be able to constrain the currently unknown ZAMS mass-BH mass relation.