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arXiv · 2605.23083

A Strongly Parametrized Mass Ratio Model for the Stable Mass Transfer Channel: a Case Study of the $10 \, \rm{M}_{\odot}$ Peak

Jaxen Godfrey·Lieke van Son·Ben Farr
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Abstract

The mass ratio of merging binary black holes (BBHs) carries information about their formation history, yet has received less attention than masses, spins and eccentricities as a channel discriminator. We derive a strongly parametrized analytical model for the mass-ratio distribution expected from the stable mass transfer (SMT) channel. The model maps mass-transfer stability and accretion efficiency onto the observed mass-ratio distribution, and naturally produces two qualitatively distinct subpopulations: a non-mass-ratio-reversed and a mass-ratio-reversed subpopulation whose distinct shapes depend on the binary-evolution parameters in a traceable way. We embed this model in a hierarchical population analysis and apply it to the $\sim 10\, \rm{M}_{\odot}$ peak in the GWTC-4 BBH catalog. We find that the data favor little to no mass-ratio reversal in this peak, and infer SMT parameters in an astrophysically plausible range. This work demonstrates how data-driven models can be used in mixtures to study singular features in BBH population data and serves as a proof of concept for how a measurement of the BBH mass-ratio distribution within a subpopulation can be translated into direct constraints on the binary-evolution physics that produced it.

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Jaxen Godfrey, Lieke van Son, Ben Farr. 2026-05-21. A Strongly Parametrized Mass Ratio Model for the Stable Mass Transfer Channel: a Case Study of the $10 \, \rm{M}_{\odot}$ Peak. https://arxiv.org/abs/2605.23083

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