Aniceto, PedroPani, PaoloRocha, Jorge V.2017-07-172017-07-172016-05-191126-6708https://hdl.handle.net/2445/113900We construct exact, time-dependent, black hole solutions of Einstein-Maxwell-dilaton theory with arbitrary dilaton coupling, a. For a = 1 this theory arises as the four-dimensional low-energy effective description of heterotic string theory. These solutions represent electrically charged, spherically symmetric black holes emitting or absorbing charged null fluids and generalize the Vaidya and Bonnor-Vaidya solutions of general relativity and of Einstein-Maxwell theory, respectively. The a = 1 case stands out as special, in the sense that it is the only choice of the coupling that allows for a time-dependent dilaton field in this class of solutions. As a by-product, when a = 1 we show that an electrically charged black hole in this theory can be overcharged by bombarding it with a stream of electrically charged null fluid, resulting in the formation of a naked singularity. This provides an example of cosmic censorship violation in an exact dynamical solution to low-energy effective string theory and in a case in which the total stress-energy tensor satisfies all energy conditions. When a ≠ 1, our solutions necessarily have a time-independent scalar field and consequently cannot be overcharged.19 p.application/pdfengcc-by (c) Aniceto, Pedro et al., 2016http://creativecommons.org/licenses/by/3.0/esForats negres (Astronomia)Espai i tempsBlack holes (Astronomy)Space and timeinfo:eu-repo/semantics/article6701862017-07-17info:eu-repo/semantics/openAccess