A Mid-Thirties Crisis: Dissecting the Properties of Gravitational Wave Sources Near the 35 Solar Mass Peak
Soumendra Kishore Roy, Lieke A. C. van Son, Will M. Farr
arXiv:2507.01086v1 Announce Type: new
Abstract: One striking feature of binary black hole (BBH) mergers observed in the first decade of gravitational-wave astronomy is an excess of events with component masses around $35,mathrm{M}_{odot}$. Multiple formation channels have been proposed to explain this excess. To distinguish among these channels, it is essential to examine their predicted population-level distributions across additional parameters. In this work, we focus on BBH mergers near the $35,mathrm{M}_{odot}$ peak and infer the population distributions of primary mass ($m_1$), mass ratio ($q$), effective spin ($chi_{rm eff}$), and redshift ($z$). We observe a gradual increase in the merger rate with $m_1$, rising by a factor of $3$ from $20,mathrm{M}_{odot}$ to a peak around $34,mathrm{M}_{odot}$, followed by a sharp, order-of-magnitude decline by $50,mathrm{M}_{odot}$. This population also shows a weak preference for equal-mass mergers and has a $chi_{rm eff}$ distribution skewed toward positive values, with a median of zero excluded at approximately $90%$ confidence. We find no significant $q-chi_{rm eff}$ correlation in the $35, mathrm{M}_{odot}$ peak population, suggesting that lower-mass systems ($m_1arXiv:2507.01086v1 Announce Type: new
Abstract: One striking feature of binary black hole (BBH) mergers observed in the first decade of gravitational-wave astronomy is an excess of events with component masses around $35,mathrm{M}_{odot}$. Multiple formation channels have been proposed to explain this excess. To distinguish among these channels, it is essential to examine their predicted population-level distributions across additional parameters. In this work, we focus on BBH mergers near the $35,mathrm{M}_{odot}$ peak and infer the population distributions of primary mass ($m_1$), mass ratio ($q$), effective spin ($chi_{rm eff}$), and redshift ($z$). We observe a gradual increase in the merger rate with $m_1$, rising by a factor of $3$ from $20,mathrm{M}_{odot}$ to a peak around $34,mathrm{M}_{odot}$, followed by a sharp, order-of-magnitude decline by $50,mathrm{M}_{odot}$. This population also shows a weak preference for equal-mass mergers and has a $chi_{rm eff}$ distribution skewed toward positive values, with a median of zero excluded at approximately $90%$ confidence. We find no significant $q-chi_{rm eff}$ correlation in the $35, mathrm{M}_{odot}$ peak population, suggesting that lower-mass systems ($m_1