Dormant Black Holes in Wide Binaries Discovered by Gaia

Gaia is a European space astrometry mission that is creating the most comprehensive and precise three-dimensional map of the Milky Way by surveying nearly two billion celestial objects. This talk will discuss one of the mission’s most remarkable achievements: the discovery of dormant stellar-mass black holes (BHs) in binary systems.

The presentation will highlight the three published systems, Gaia BH1, Gaia BH2, and Gaia BH3, which have orbital periods ranging from 180 to 4,000 days. In addition, the upcoming Gaia data release, scheduled for 2 December, is expected to reveal several dozen additional black-hole candidates.

These discoveries provide the first glimpse of a previously hidden population of dormant black holes in wide binaries, challenging existing models of binary evolution and suggesting unexpected evolutionary pathways. Gaia BH3, with a mass of approximately 33 M⊙, is more massive than any other known stellar-origin black hole in the Milky Way. Remarkably, its mass coincides with the peak of the black-hole mass distribution inferred from extragalactic mergers detected through gravitational waves, establishing an intriguing link between Galactic black holes and those observed by gravitational-wave observatories.