Predictions of a simple parametric model of hierarchical black hole mergers

Understand

Hierarchical mergers of black holes are proposed as a mechanism to explain the observations of binary black holes with component masses between $\sim 50M_{\odot}\hbox{--}130M_{\odot}$ by LIGO/Virgo, often referred to as "upper mass gap".

• We study the efficiency with which hierarchical mergers can produce higher and higher masses using a simple model of the forward evolution of binary black hole populations in gravitationally bound systems like stellar clusters.
• The model relies on pairing probability and initial mass functions for the black hole population, along with numerical relativity fitting formulas for the mass, spin, and kick speed of the merger remnant.
• We carry out an extensive comparison of the predictions of our model with clusterBHBdynamics (cBHBd) model, a fast method for the evolution of star clusters and black holes therein.