The Mass-Ratio Distribution of the Low-Mass Binary Black Hole Subpopulation: A Natural Outcome of Isolated Binary Evolution
Abstract
The observed merging binary black hole population is increasingly consistent with being composed of a mixture of subpopulations, each likely the result of different formation mechanisms. In particular, the low-mass subpopulation, with primary black hole masses below approxeq 15 M⊙, has been attributed to mergers formed through isolated binary evolution. We use the binary population synthesis code POSYDON to study the mass ratio (q) distribution of binary black hole mergers from isolated binary evolution and compare to the observed low-mass subpopulation. We explore variations in supernova remnant prescriptions, common-envelope efficiency, and black hole accretion efficiency. We find that our models have a preference for asymmetric q, most with a broad peak near qapproxeq0.5−0.7, and a near-equal-mass component whose relative strength varies across models. This resultant q distribution is consistent with the q distribution of the low-mass subpopulation observed with gravitational waves. We find that for the majority of models these features arise from physically distinct formation subchannels: the asymmetric peak reflects contributions from common-envelope and stable mass-transfer systems, while the near-equal-mass component traces double-core common envelope and contact systems. We conclude that the features in the q distribution of the observed low-mass subpopulation emerge naturally from isolated binary evolution across a range of model assumptions. As the gravitational-wave catalog continues to grow, the relative strength of these q features will provide an increasingly powerful diagnostic of isolated binary evolution and its formation subchannels.
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BibTeX
@misc{gallegosgarcia2026massratio,
title = {{The Mass-Ratio Distribution of the Low-Mass Binary Black Hole Subpopulation: A Natural Outcome of Isolated Binary Evolution}},
author = {Monica Gallegos-Garcia and Anarya Ray and Vicky Kalogera and Max Briel and Michael Zevin and Abhishek Chattaraj and Zepei Xing and Jeff J. Andrews and Seth Gossage and Philipp M. Srivastava},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.01784},
eprint = {2609.01784},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.01784},
}
RIS
TY - UNPB
TI - The Mass-Ratio Distribution of the Low-Mass Binary Black Hole Subpopulation: A Natural Outcome of Isolated Binary Evolution
AU - Monica Gallegos-Garcia
AU - Anarya Ray
AU - Vicky Kalogera
AU - Max Briel
AU - Michael Zevin
AU - Abhishek Chattaraj
AU - Zepei Xing
AU - Jeff J. Andrews
AU - Seth Gossage
AU - Philipp M. Srivastava
PY - 2026
DA - 2026/09/01
PB - arXiv
DO - 10.48550/arxiv.2609.01784
UR - https://arxiv.org/abs/2609.01784
AB - The observed merging binary black hole population is increasingly consistent with being composed of a mixture of subpopulations, each likely the result of different formation mechanisms. In particular, the low-mass subpopulation, with primary black hole masses below approxeq 15 M_⊙, has been attributed to mergers formed through isolated binary evolution. We use the binary population synthesis code POSYDON to study the mass ratio (q) distribution of binary black hole mergers from isolated binary evolution and compare to the observed low-mass subpopulation. We explore variations in supernova remnant prescriptions, common-envelope efficiency, and black hole accretion efficiency. We find that our models have a preference for asymmetric q, most with a broad peak near qapproxeq0.5−0.7, and a near-equal-mass component whose relative strength varies across models. This resultant q distribution is consistent with the q distribution of the low-mass subpopulation observed with gravitational waves. We find that for the majority of models these features arise from physically distinct formation subchannels: the asymmetric peak reflects contributions from common-envelope and stable mass-transfer systems, while the near-equal-mass component traces double-core common envelope and contact systems. We conclude that the features in the q distribution of the observed low-mass subpopulation emerge naturally from isolated binary evolution across a range of model assumptions. As the gravitational-wave catalog continues to grow, the relative strength of these q features will provide an increasingly powerful diagnostic of isolated binary evolution and its formation subchannels.
ER -