GW241011 and GW241110: Hints of Hierarchical Mergers from the Merger Entropy Index

Abstract

GW241011 and GW241110 both exhibit extremely asymmetric masses, high primary spins, and significant spin-orbit misalignment, which challenge the formation of first-generation binary black hole mergers formed from stellar collapse. This implies that these two gravitational wave events might originate from the hierarchical merger mechanism, with at least one of the black holes being the remnant of a previous merger. Here we investigate the origin of hierarchical mergers for GW241011 and GW241110 using the merger entropy index which measures the efficiency of entropy transfer for binary black hole mergers in general relativity. We find that GW241011 is consistent with hierarchical mergers in dense star clusters. The origin of GW241110 remains under debate due to its large distribution uncertainty, which leads to method-dependent inference and should be taken into account when interpreting this event in terms of hierarchical mergers.