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 ~55 M⊙ for the second power law, consistent with the onset of a pair-instability supernova mass gap.