Mass-Ratio Reversal as an Alternative to Hierarchical Mergers for GW241011

Abstract

Recent gravitational-wave (GW) observations have revealed binary black hole (BBH) mergers with both extreme mass ratios and large effective spin parameters ($\chi_{\rm{eff}}$). GW241011 is a notable example that shows these properties. Although hierarchical mergers (second-generation + first-generation BHs) can naturally produce high spins and become more prevalent than first-generation + first-generation mergers at mass ratios $q \lesssim 0.6$, they are negligible at the extreme mass ratio $\sim 0.3$ and are further limited by gravitational recoil kicks that can eject the second-generation BH from the host environment. Moreover, recent studies have argued against a dynamical origin for GW241011. Here, we investigate the formation of GW241011-like systems through the mass-ratio reversal (MRR) channel in isolated binary evolution. By quantifying the probability of producing such systems across a range of binary-evolution models, we identify the key dependencies on stellar-evolution and binary-interaction physics. Our results demonstrate the conditions under which the MRR channel can provide a viable alternative to hierarchical mergers for GW241011-like events, although its predicted merger rate density remains relatively low.