New MESA stellar tracks with varied winds and convective mixing produce a primary black hole mass function with twin peaks near 8 and 13 solar masses in most variations, the higher peak dominated by mass-ratio-reversal systems, with rates varying by a factor of six.
A Strongly Parametrized Mass Ratio Model for the Stable Mass Transfer Channel: a Case Study of the $10 \, \rm{M}_{\odot}$ Peak
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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.
years
2026 2representative citing papers
Stable mass transfer produces two distinct peaks in merging binary black hole primary mass and mass ratio distributions via mass ratio reversal under conservative mass transfer.
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Twin Peaks: Resolving Features in the Binary Black Hole Mass Function with COSMIC-METISSE
New MESA stellar tracks with varied winds and convective mixing produce a primary black hole mass function with twin peaks near 8 and 13 solar masses in most variations, the higher peak dominated by mass-ratio-reversal systems, with rates varying by a factor of six.
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A Stellar Role Reversal: Multiple Features in the Mass and Mass Ratio Distributions of Merging Binary Black Holes from Stable Mass Transfer
Stable mass transfer produces two distinct peaks in merging binary black hole primary mass and mass ratio distributions via mass ratio reversal under conservative mass transfer.