Clarifications on black/white hole metastable relics as dark matter

The idea that the evaporation of black holes could end around the Planck mass and lead to relics possibly accounting for dark matter is quite old. In this article we focus on new models where the relics are metastable, typically with a lifetime of order $M^5$, where $M$ is the initial mass of the black hole. We show that those relics would actually be quite luminous, radiating – possibly as much as the stars – in the optical or UV band. We explicitly construct a proposal for their direct detection.