The branching ratio of LIGO binary black holes

Understand

Formation of binary black holes (BBHs) detected by gravitational-wave (GW) observations could be broadly divided into two categories: those formed through field binary evolution and those assembled dynamically in dense stellar systems.

• The branching ratio of the BBHs refers to the contribution of each channel.
• The dynamical assembly channel would predict a symmetric distribution in the effective spins of the BBHs while field formation predicts BBHs to have positive effective spins.
• By modeling these two populations based on their effective spin distribution we show that in the 10 BBHs detected by LIGO/Virgo the contribution of the dynamically assembled BBHs to be more than about 50\% with 90\% confidence.