Shadows of a generic class of spherically symmetric, static spacetimes

TL;DR

This paper investigates the shadows cast by a broad class of spherically symmetric, static spacetimes, analyzing how their parameters influence shadow size and linking these to potential observational signatures in various gravity theories.

Contribution

It introduces a general metric form with adjustable parameters, explores energy conditions, and connects shadow features to different gravitational theories and observational data.

Findings

Shadow radius depends on metric parameters within energy condition constraints

Certain parameter choices produce shadows consistent with recent observations

Metrics may originate from various gravity theories and physical scenarios

Abstract

We explore the characteristics of shadows for a general class of spherically symmetric, static spacetimes, which may arise in general relativity or in modified theories of gravity. The chosen line element involves a sum (with constant but different coefficients) of integer powers of $\frac{1}{\text{r}}$ in $\text{g}_\text{tt}$ and $\text{g}_\text{rr}$, in the Schwarzschild gauge. We begin our discussion by motivating the line element through a study of the energy conditions (null and weak) and the extent to which they are satisfied/violated for diverse choices of the parameters appearing in the metric functions. Subsequently, we construct the circular shadows and analyse the dependence of the shadow radius on the metric parameters. We find that with specific choices of the metric parameters (within the ranges allowed by the energy conditions) one can, in principle, obtain values that conform with recent observations on shadows, as available in the literature. We also mention where such metrics may arise (i.e., in which theory of gravity and the physical scenario therein), thereby proposing that the observed shadows may be representative signatures of different theoretical contexts.