2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/201102We present a solution to the vacuum Einstein Equations which represents a collapse of a gravitational wave in 5 dimensions. Depending on the focal length of the wave, the collapse results, either in a black string covered by a horizon, or in a naked singularity which can be removed.Minor changes. A reference added. Matches the print version. To appear in Phys. Lett. AGeneral Relativity and Quantum CosmologyHigh Energy Physics - Theorytext