Maxime Gadioux, Harvey S. Reall, Jorge E. Santos
An extremal Reissner-Nordström black hole can form in finite time in the gravitational collapse of a massless charged scalar field. The proof of this is based on the method of characteristic gluing, which involves making an for the scalar field at the horizon. We perform a numerical investigation of the characteristic gluing procedure for several different . In each case, gluing is possible only if the final black hole mass is large enough. We find that the minimum required mass varies significantly for different . We also consider the effect of including a mass term for the scalar field. In this case, for each we determine the maximum mass-to-charge ratio for the scalar field such that gluing is possible. Analogous results are obtained for a nonzero cosmological constant.