Search for a Black Hole Binary in Gaia DR3 Astrometric Binary Stars with Spectroscopic Data

Abstract We report the discovery of a candidate binary system consisting black hole (BH) and red giant branch star in Gaia DR3. This was discovered from 64,108 solutions for which both astrometric spectroscopic data are available. For this system, consistent with each other, making confident BH binary. The primary (visible) DR3 5870569352746779008, is whose mass quite uncertain. Fortunately, despite uncertainty primary’s mass, we can estimate secondary (dark) object to be >5.68 M ? probability 99%, based on orbital parameters. much larger than maximum neutron (?2.0 ), indicates that likely BH. argue that, if dark not BH, must more exotic orbits around quadruple (or higher-order multiple-star system) total 5.68 . If genuine binary, has longest period (1352.22 ± 45.81 days) among those so far. As our conclusion entirely relies data, independent confirmation follow-up observations (e.g., long-term time-series spectra) desired.