In this second part of a two-part paper, we discuss numerical simulations of a head-on merger of two nonspinning black holes. We resolve the fate of the original two apparent horizons by showing that after intersecting, their world tubes “turn around” and continue backwards in time. Using the method presented in the first paper [Phys. Rev. D 084083 (2021)] to locate these surfaces, we resolve several such world tubes evolving and connecting through various bifurcations and annihilations. This also draws a consistent picture of the full merger in terms of apparent horizons, or more generally, marginally outer trapped surfaces (MOTSs). The MOTS stability operator provides a natural mechanism to identify MOTSs which should be thought of as black hole boundaries. These are the two initial ones and the final remnant. All other MOTSs lie in the interior and are neither stable nor inner trapped.

• Received 30 May 2021
• Accepted 8 September 2021

DOI:https://doi.org/10.1103/PhysRevD.104.084084