"Binary black hole merger rates: the role of the metal-dependent star formation rate"
Abstract: As the number of gravitational-wave detections of binary black hole (BBH) mergers continue to rise, so do the challenges in reconciling theoretical models with observations. A key factor shaping BBH merger rates is the metal-dependent star formation rate (SFR), as metallicity plays a crucial role in the evolution of massive stars. Our analysis reveals a striking discrepancy: when accounting for a realistic metal-dependent SFR evolution, the predicted BBH merger rate density exceeds that inferred from gravitational-wave data. The source of this tension does not lie in the treatment of the metal-dependent SFR but rather stems from stellar evolution models and/or BBH formation channels. I will discuss the astrophysical implications of these results as well as potential solutions to this mismatch.