Hunting black holes with Gaia

Abstract

We predict the number of black holes with stellar companions that are potentially detectable with Gaia astrometry over the course of its 5-yr mission. Our model estimates that nearly 2 × 10⁵ astrometric binaries hosting black holes and stellar companions brighter than Gaia's detection threshold, G ∼ 20, should be discovered with 5σ sensitivity. Among these detectable binaries, systems with longer orbital periods are favoured, and black hole and stellar companion masses in the range M_BH ∼ 6-10 M_⊙ and M_* ∼ 1-2 M_⊙, respectively, are expected to dominate.