An upper limit on Galactic OB+black hole binaries from SDSS-V
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 (≥ 10 M⊙) OB stars with a close BH companion, fBH. 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 fBH ≲ 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.
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BibTeX
@misc{mullerhorn2026upper,
title = {{An upper limit on Galactic OB+black hole binaries from SDSS-V}},
author = {J. Müller-Horn and H. -W. Rix and S. Shahaf and B. Pennell and E. Zari and M. C. Ramírez-Tannus and A. Farah and R. Essick and J. I. Villaseñor and M. R. Blanton and J. G. Fernández-Trincado and J. A. Kollmeier and C. Lam and K. Maltsev and A. Roman-Lopes and D. P. Schneider and A. Tkachenko},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.17253},
eprint = {2610.17253},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.17253},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - An upper limit on Galactic OB+black hole binaries from SDSS-V
AU - J. Müller-Horn
AU - H. -W. Rix
AU - S. Shahaf
AU - B. Pennell
AU - E. Zari
AU - M. C. Ramírez-Tannus
AU - A. Farah
AU - R. Essick
AU - J. I. Villaseñor
AU - M. R. Blanton
AU - J. G. Fernández-Trincado
AU - J. A. Kollmeier
AU - C. Lam
AU - K. Maltsev
AU - A. Roman-Lopes
AU - D. P. Schneider
AU - A. Tkachenko
PY - 2026
DA - 2026/10/12
PB - arXiv
DO - 10.48550/arxiv.2610.17253
UR - https://arxiv.org/abs/2610.17253
AB - 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 (≥ 10 M_⊙) OB stars with a close BH companion, f_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_BH ≲ 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.
ER -