The possible existence of naked singularities, hypothetical astrophysical objects, characterized by a gravitational singularity without an event horizon is still an open problem in present day astrophysics. From an observational point of view distinguishing between astrophysical black holes and naked singularities also represents a major challenge. One possible way of differentiating naked singularities from black holes is through the comparative study of thin accretion disks properties around these different types of compact objects. In the present paper we continue the comparative investigation of accretion disk properties around axially-symmetric rotating geometries in Brans—Dicke theory in the presence of a massless scalar field. Due to the differences in the exterior geometries between black holes and Brans—Dicke—Kerr naked singularities, the thermodynamic and electromagnetic properties of the disks energy flux, temperature distribution and equilibrium radiation spectrum are different for these two classes of compact objects, consequently giving clear observational signatures that could discriminate between black holes and naked singularities. The standard assumption about such objects is that they must be black holes, that is, objects whose surface is covered by an event horizon.
Dangerous 'naked' black holes could be hiding in the universe
Solutions of Kerr Black Holes subject to Naked Singularity and Wormholes - Authorea
Black holes are regions of infinite density, known as a singularity. And according to mainstream physics, each of these cosmic matter munchers is fringed by an event horizon —- a boundary where once you fall in, you never come out. But what if some black holes are naked — completely lacking such frontiers? As far as we can tell, singularities are always wrapped in event horizons, but a more detailed look at the math of general relativity suggests that doesn't have to be the case. If such naked black holes dot the universe, new research reveals how we might be able to detect one: by looking at the ring of light surrounding it.