Year: 2026
Type: preprint
Abstract: Binaries composed of a luminous OB star and a black hole (BH) are a key evolutionary link between massive stellar binaries and merging compact-object binaries, but only a handful are known and their occurrence fraction remains poorly constrained. We use multi-epoch spectroscopy from the SDSS-V Milky Way Mapper to place a first rigorous empirical upper limit on the fraction of Galactic massive ($\geq 10\,\mathrm{M}_\odot$) OB stars with a close BH companion, $f_\mathrm{BH}$. Radial-velocity (RV) variability alone cannot distinguish BH companions from the far more numerous luminous binaries. We therefore combine the SDSS-V RV variability measurements of 3130 massive OB stars with high-resolution follow-up and literature information to identify luminous companions among the RV-variable subset. Forward-modelling the detectability of OB+BH systems using BH masses and orbital parameters from binary-evolution models, we find $f_\mathrm{BH} \lesssim 3\%$ at 95% credibility. This empirical upper limit approaches, but does not exclude, theoretical predictions for the OB+BH fraction. The constraint is primarily limited by the number of RV-variable systems that can be decisively classified, highlighting the importance of complete, high-quality follow-up for future searches.
Source: arXiv (Cornell University)
Institutions: Heidelberg University, Max Planck Institute for Astronomy, Arcetri Astrophysical Observatory, National Institute for Astrophysics, University of Toronto, Canadian Institute for Theoretical Astrophysics, Carnegie Institution for Science, Carnegie Observatories, Universidad Bernardo O'Higgins, University of La Serena, Pennsylvania State University, KU Leuven
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, Alfred P. Sloan Foundation, Yale University, Carnegie Institution of Washington, Ohio State University, California Institute of Technology, Harvard University, Johns Hopkins University, New Mexico State University, Space Telescope Science Institute, Flatiron Health, École Polytechnique Fédérale de Lausanne, University of Toronto, Universidad Nacional Autónoma de México, Yunnan University, Nanjing University, China National Textile and Apparel Council, Leibniz-Institut für Astrophysik Potsdam, Max-Planck-Institut für Astronomie, University of Illinois at Urbana-Champaign, University of Colorado Boulder, Smithsonian Astrophysical Observatory, Leibniz-Gemeinschaft, National Astronomical Observatories, Chinese Academy of Sciences, Kavli Institute for Theoretical Physics, University of California, Santa Barbara
OpenAlex ID: W7221820855