Kerr-MOG-(A)dS black hole and its shadow in scalar-tensor-vector gravity theory

TL;DR

This paper constructs and analyzes rotating black hole solutions in scalar-tensor-vector gravity, exploring how their shadows are affected by the MOG parameter and cosmological constant, with implications for observational signatures and constraints.

Contribution

It introduces Kerr-MOG-(A)dS black hole solutions in STVG theory and studies their shadows, revealing effects of modified gravity parameters on observable features.

Findings

Black hole shadow size decreases with increasing cosmological constant.

Shadow expands with increasing MOG parameter, reaching a maximum.

Numerical ray-tracing distinguishes degeneracy between parameters.

Abstract

The scalar-tensor-vector gravity (STVG) theory has attracted significant interest due to its ability to effectively address the issue of galaxy rotation curves and clusters of galaxies without considering the influence of dark matter. In this paper, we construct rotating black hole solutions with a cosmological constant in the STVG theory (i.e., Kerr-MOG-(A)dS black hole solutions), where the import of a gravitational charge as a source modifies the gravitational constant, determined by $ G=G_{\text{N}}(1+\alpha) $. For Kerr-MOG-dS spacetime, the observer is situated at a specific location within the domain of outer communication, rather than being located infinitely far away. Since black hole shadows are shaped by light propagation in spacetime, the interaction between the MOG parameter and the cosmological constant is expected to produce novel effects on these shadows. As the cosmological constant $\Lambda$ increases, the apparent size of the black hole shadow decreases. Additionally, the shadow expands with an increase in the MOG parameter $\alpha$, reaching a maximum at a certain value, and its shape becomes more rounded under an arbitrary rotation parameter, which leads to degeneracy between different black hole parameters. However, by employing numerical ray-tracing techniques, we have found that gravitational lensing and the frame-dragging effect effectively distinguish this degeneracy. Our work contributes to a deeper understanding of black holes in modified gravity, their observational signatures, and constraints.