Shadows of naked singularity in Brans-Dicke gravity

TL;DR

This paper explores how naked singularities in Brans-Dicke gravity can produce shadow features similar to black holes, with potential implications for interpreting EHT observations.

Contribution

It demonstrates that Brans-Dicke naked singularities can create observable shadows, expanding the understanding of possible compact objects beyond traditional black holes.

Findings

BD naked singularities can produce smaller shadows than Schwarzschild black holes.

Parameter space $-3/2 < mbda < 0$ yields physically viable solutions.

Shadow features depend on the BD parameter mbda and can mimic black hole images.

Abstract

We investigate the observational features of exact vacuum solutions in Brans-Dicke (BD) gravity, focusing on their implications for black hole shadow imaging. Motivated by the Event Horizon Telescope (EHT) observations, we revisit a class of BD solutions that exhibit a naked singularity. These solutions, despite lacking a conventional event horizon, exhibit photon spheres and produce shadow-like features. We analyze null geodesics and perform ray-tracing simulations under a simplified, optically thin accretion disk model to generate synthetic images. Our results show that BD naked singularities can cast shadows smaller than those of Schwarzschild black holes of equivalent mass. We identify the parameter space $-3/2 < \omega < 0$ as physically viable, ensuring attractive gravity and the absence of ghost fields. These findings suggest that BD naked singularities are possible candidates for compact astrophysical objects.