Speaker
Description
The latest LIGO-Virgo-KAGRA observational run has narrowed the local binary black hole merger rate to 14-26 Gpc$^{-3}$ yr$^{-1}$. Despite the increasing number of observations, current state-of-the-art binary population synthesis codes tend to overestimate this rate, revealing a tension between theoretical models and gravitational wave data.
In this talk, I identify and discuss the primary drivers of this discrepancy. A key factor shaping binary black hole merger rates is the metal-dependent star formation rate, as metallicity plays a crucial role in the evolution and fate of massive stars. I will demonstrate that the over-prediction cannot be reconciled solely by adjusting the metal-dependent star formation rate history. Instead, the tension points toward gaps in our understanding of binary evolution.
I will provide a systematic review of the binary evolution uncertainties at play, focusing on the main ingredients that can alleviate this tension, from the common envelope evolution physics and physics of mass transfer, to the natal kicks. Finally, recent observations of dormant black holes by Gaia provide further insights into the formation channels of black hole binaries. I will explore how these data can complement gravitational wave observations and help shed light on the formation and evolution of merging binary black holes.