Observing naked singularities by the present and next-generation Event Horizon Telescope

Abstract: We consider the observational signatures of reflective naked singularities as seen by the current and next-generation Event Horizon Telescope (EHT). The reflective naked singularities lead to a distinctive morphology of their accretion disk images producing a series of bright rings at the central part of the image. We explore the capacity of the present and near-future EHT arrays to detect this structure considering two particular naked singularity spacetimes and modeling the galactic target M87*. We obtain that the 2017 EHT array is incapable of resolving the bright ring series. However, it detects an increased overall intensity of the central brightness depression reaching with an order of magnitude higher values than for the Kerr black hole. This metric can be used as a quantitative measure for the absence of an event horizon. The observations with the next-generation EHT at 230 GHz would reveal two orders of magnitude difference in the intensity of the central brightness depression between naked singularities and black holes. Introducing a second observational frequency at 345 GHz would already resolve qualitative effects in the morphology of the disk image for naked singularities as certain bright spots become apparent at the center of the image.