Marginally outer trapped (open) surfaces in 4+1 dimensional spacetimes

In binary black hole mergers and other highly dynamical spacetimes, the surface of most obvious interest, the event horizon, is often computationally difficult to locate. Instead, it is useful to use quasi-local characterizations of black hole boundaries, such as Marginally Outer Trapped Surfaces (MOTS), the outer-most of which is (often) the apparent horizon. Recent studies have shown that MOTS not only characterize boundaries, but may also be found in black hole interiors. This has been seen in 4D Schwarzschild and Reissner-Nordstrom, as well as in binary black hole mergers. In this thesis, behaviours of MOTS|and their open generalization, Marginally Outer Trapped Open Surfaces (MOTOS)|in the interior of five-dimensional black holes are studied; both static (Schwarzschild), and rotating (Myers-Perry). Similar to four-dimensions, we find infinitely many self-intersecting MOTS in 5D Schwarzschild. We find finitely many self-intersecting MOTS in Myers-Perry, finding fewer as the rotation increases. However, we do find oscillations of the MOTOS, which is novel behaviour