Interior dynamics of neutral and charged black holes

In this paper, we explore the interior dynamics of neutral and charged black holes. Scalar collapses in flat, Schwarzschild, and Reissner-Nordstr\"om background geometries are simulated. We examine the dynamics in the vicinities of the central singularity of a Schwarzschild black hole and of the inner horizon of a Reissner-Nordstr\"om black hole. In simulating scalar collapses in Schwarzschild and Reissner-Nordstr\"om geometries, Kruskal and Kruskal-like coordinates are used, respectively, with the presence of a scalar field being taken into account. It is found that, besides near the inner horizons of Reissner-Nordstr\"om and Kerr black holes, mass inflation also takes place near the central singularity in neutral scalar collapse. Approximate analytic expressions for different types of mass inflation are partially obtained via a close interplay between numerical and analytical approaches and an examination of the connections between Schwarzschild black holes, Reissner-Nordstr\"om black holes, neutral collapse, and charge scattering. We argue that the mass inflations near the central singularity and the inner horizon are related to the localness of the dynamics in strong gravity regions. This is in accord with the Belinskii, Khalatnikov, and Lifshitz conjecture.