Black holes immersed in modified Chaplygin-like dark fluid and cloud of strings: geodesics, shadows, and images

TL;DR

This paper explores how a modified Chaplygin-like dark fluid and a cloud of strings affect black hole properties, including geodesics, shadows, and images, providing insights into observational signatures and parameter constraints.

Contribution

It introduces a detailed analysis of black holes immersed in a MCDF and string cloud, examining their geodesic structure, shadow formation, and observational features, with parameter constraints based on Sgr A* and M87* data.

Findings

Existence of stable circular orbits depends on MCDF and string cloud parameters.

Shadow sizes are constrained by the influence of the MCDF and string cloud.

Brightness mainly from direct emission, with negligible photon ring contribution.

Abstract

This study investigates a black hole surrounded by a cloud of strings and a cosmological dark fluid characterized by a modified Chaplygin-like equation of state (MCDF), $p=A\rho-B/\rho^{\beta}$. We analyze its geodesic structure, shadow, and optical appearance. Analysis of the effective potential and epicyclic frequencies reveals that the existence of innermost/outermost stable circular orbits (ISCOs/OSCOs) for timelike particles is controlled by the parameters of the MCDF and the cloud of strings. The behavior of orbital conserved quantities and the Keplerian frequency are also examined. By equating the influence of the MCDF on the spacetime metric at spatial infinity with that of a cosmological constant, we constrain the MCDF parameters using the observed shadow radii of Sgr A* and M87*. We investigate the effects of the cloud of strings and MCDF on the black hole's shadows and optical images, assuming various thin disk accretion profiles. Using the method developed by Wald and collaborators, light trajectories are classified by their impact parameters into direct emission, the lensing ring, and the photon ring. The presence of OSCOs can lead to the existence of outer edges in the direct emission and lensing ring images. Observed brightness primarily originates from direct emission, with a minor contribution from the lensing ring, while the photon ring's contribution is negligible due to extreme demagnification. The influence of the cloud of strings and MCDF parameters on all results is analyzed throughout the study.