A new bump in the night: evidence of a new feature in the binary black hole mass distribution at 70~M_ from gravitational-wave observations

We analyze the confident binary black hole (BBH) detections from the third Gravitational-Wave Transient Catalog (GWTC-3) with an alternative mass population model in order to capture features in the mass distribution beyond the Powerlaw + Peak model. We find that the peak of a second power law characterizes the ~ 30-35~ M_ bump, such that the data marginally prefers a mixture of two power laws for the mass distribution of binary components over a Powerlaw + Peak model with a Bayes Factor log₁₀B of 0.1. This result may imply that the ~ 30-35~ M_ feature represents the onset of a second population of BBH mergers (e.g. from a dynamical formation channel) rather than a specific mass feature over a broader distribution. When an additional Gaussian bump is allowed within our power law mixture model, we find a new feature in the BH mass spectrum at ~65-70~M_. This new feature may be consistent with hierarchical mergers, and constitute ~2% of the BBH population. This model also recovers a maximum mass of 58⁺³⁰₋₁₄~M_ for the second power law, consistent with the onset of a pair-instability supernova mass gap.