Generality of QLHS features beyond head-on collisions

Ascertain whether the qualitative features of quasi-local horizon segments observed in head-on collisions of non-spinning black holes—including the behavior and spectrum of the stability operator—persist generically when spins are allowed and beyond head-on configurations.

Background

High-precision numerical studies of Brill–Lindquist head-on collisions reveal rich MTS dynamics: birth of common horizons with vanishing principal eigenvalue, subsequent bifurcations linked to higher eigenvalues, inner horizon complexities including self-intersections, and stable outer horizons approaching equilibrium.

These results were obtained in non-spinning, axisymmetric settings where the stability operator has real spectrum. Extending them to generic spinning binaries requires understanding potentially complex spectra and different qualitative behaviors.