{"paper":{"title":"The Mass-Ratio Distribution of the Low-Mass Binary Black Hole Subpopulation: A Natural Outcome of Isolated Binary Evolution","arxiv_id":"2609.01784","primary_cat":"astro-ph.HE","submitted_at":"2026-09-01T18:54:37+00:00","version_compiled":"v1"},"notice":"Every quoted sentence is the authors' text from the arXiv listing abstract. Labels and probabilities are the outputs of classifier-1.13.0 on the question bank abstract-p1-20260923, exactly as returned. No sentence in this record was written by a language model.","schema":"pith.compiled-record/v0","status":"compiled","abstract":{"source":"arXiv listing abstract v1","sentences":[{"i":0,"p":1.0,"id":"s0","own":false,"role":"background","text":"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.","hedge":{"p":0.93,"label":"hedged_possibility"},"own_p":0.07,"main_claim_p":0.03,"quantitative":false,"quantitative_p":0.08,"role_probabilities":{"gap":0.0,"method":0.0,"result":0.0,"background":1.0,"limitation":0.0,"future_work":0.0,"contribution":0.0,"interpretation":0.0}},{"i":1,"p":1.0,"id":"s1","own":false,"role":"background","text":"In particular, the low-mass subpopulation, with primary black hole masses below $\\approxeq 15\\,M_{\\odot}$, has been attributed to mergers formed through isolated binary evolution.","hedge":{"p":0.6,"label":"hedged_possibility"},"own_p":0.05,"main_claim_p":0.03,"quantitative":true,"quantitative_p":0.97,"role_probabilities":{"gap":0.0,"method":0.0,"result":0.0,"background":1.0,"limitation":0.0,"future_work":0.0,"contribution":0.0,"interpretation":0.0}},{"i":2,"p":0.63,"id":"s2","own":true,"role":"method","text":"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.","hedge":{"p":0.96,"label":"asserted"},"own_p":0.95,"main_claim_p":0.02,"quantitative":false,"quantitative_p":0.23,"role_probabilities":{"gap":0.0,"method":0.63,"result":0.0,"background":0.0,"limitation":0.0,"future_work":0.0,"contribution":0.37,"interpretation":0.0}},{"i":3,"p":0.92,"id":"s3","own":true,"role":"method","text":"We explore variations in supernova remnant prescriptions, common-envelope efficiency, and black hole accretion efficiency.","hedge":{"p":0.6,"label":"asserted"},"own_p":0.87,"main_claim_p":0.01,"quantitative":false,"quantitative_p":0.03,"role_probabilities":{"gap":0.0,"method":0.92,"result":0.0,"background":0.0,"limitation":0.0,"future_work":0.0,"contribution":0.08,"interpretation":0.0}},{"i":4,"p":1.0,"id":"s4","own":true,"role":"result","text":"We find that our models have a preference for asymmetric $q$, most with a broad peak near $q\\approxeq0.5-0.7$, and a near-equal-mass component whose relative strength varies across models.","hedge":{"p":0.98,"label":"asserted"},"own_p":0.97,"main_claim_p":0.12,"quantitative":true,"quantitative_p":0.92,"role_probabilities":{"gap":0.0,"method":0.0,"result":1.0,"background":0.0,"limitation":0.0,"future_work":0.0,"contribution":0.0,"interpretation":0.0}},{"i":5,"p":0.73,"id":"s5","own":true,"role":"result","text":"This resultant $q$ distribution is consistent with the $q$ distribution of the low-mass subpopulation observed with gravitational waves.","hedge":{"p":0.76,"label":"hedged_possibility"},"own_p":0.72,"main_claim_p":0.2,"quantitative":true,"quantitative_p":0.66,"role_probabilities":{"gap":0.0,"method":0.0,"result":0.73,"background":0.0,"limitation":0.0,"future_work":0.0,"contribution":0.0,"interpretation":0.27}},{"i":6,"p":0.86,"id":"s6","own":true,"role":"interpretation","text":"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.","hedge":{"p":1.0,"label":"asserted"},"own_p":0.95,"main_claim_p":0.12,"quantitative":false,"quantitative_p":0.17,"role_probabilities":{"gap":0.0,"method":0.0,"result":0.14,"background":0.0,"limitation":0.0,"future_work":0.0,"contribution":0.0,"interpretation":0.86}},{"i":7,"p":0.95,"id":"s7","own":true,"role":"interpretation","text":"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.","hedge":{"p":0.99,"label":"asserted"},"own_p":0.78,"main_claim_p":0.95,"quantitative":false,"quantitative_p":0.07,"role_probabilities":{"gap":0.0,"method":0.0,"result":0.05,"background":0.0,"limitation":0.0,"future_work":0.0,"contribution":0.0,"interpretation":0.95}},{"i":8,"p":0.8,"id":"s8","own":false,"role":"future_work","text":"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 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