Can we distinguish black holes from naked singularities by the images of their accretion disks?

TL;DR

This paper compares images of accretion disks around black holes and naked singularities, finding that certain naked singularity models can mimic black hole images, while others produce distinguishable features.

Contribution

It provides a detailed analysis of accretion disk images around different compact objects, highlighting potential observational signatures to differentiate black holes from naked singularities.

Findings

Naked singularities with photon spheres can mimic black hole images.

Naked singularities without photon spheres produce distinguishable images.

Different naked singularity models can be distinguished through their accretion disk images.

Abstract

We study here images of thin accretion disks around black holes and two classes of naked singularity spacetimes and compare these scenarios. The naked singularity models which have photon spheres have single accretion disk with its inner edge lying outside the photon sphere. The images and shadows created by these models mimic those of black holes. It follows, therefore, that further and more detailed analysis of the images and shadows structure in such case is needed to confirm or otherwise the existence of an event horizon for the compact objects such as the galactic centers. However, naked singularity models which do not have any photon spheres can have either double disks or a single disk extending up to the singularity. The images obtained from such models significantly differ from those of black holes. Moreover, the images of the two classes of naked singularities in this latter case, differ also from one another, thereby allowing them to be distinguish from one another through the observation of the images.