Shadow and Thermodynamics of deformed Schwarzschild-AdS black hole with a Cloud of Strings embedded in Perfect Fluid Dark Matter

Abstract

We investigate the optical and thermodynamic properties of a deformed Schwarzschild Anti-de Sitter (AdS) black hole coupled to a cloud of strings and embedded in perfect fluid dark matter. We analyze the photon sphere and the corresponding black hole shadow, determining how these observables are affected by the string cloud, dark matter distribution, and geometric deformation. The thermodynamic behavior is studied through both the quasi-homogeneous fundamental equation within the classical physical approach and the geometric framework of geometrothermodynamics (GTD), showing full consistency between the two descriptions. In the extended phase space, we examine the critical structure and phase behavior of the system. Our analysis reveals that neither the geometric deformation nor the dark matter parameter generates new phase transitions; criticality emerges only in the vicinity of the Reissner--Nordström--AdS solution (RN--AdS), where the deformation parameter effectively plays the role of an electric charge squared. These results clarify the interplay between matter distributions, geometric deformations, and the phase structure of AdS black holes.

Figures (10)

• Figure 2: Behavior of the effective potential as a function of dimensonless radial distance $r/M$ for various values of $\lambda,\,\beta$ and $\gamma$. Here $\alpha/M=1,\,\mathrm{L}=1$.
• Figure 3: Photon sphere radius as a function of $\beta/M$ and $\gamma$ for two values of $\lambda/M$. Here $\alpha=1$.
• Figure 4: Shadow radius as a function of $\beta/M$ and $\gamma$ for two values of $\lambda/M$. Here $\alpha/M=1,\,r_O/M=50$.
• Figure 5: Thermodynamic functions of the deformed AdS black hole: (i) temperature $T(S)$, (ii) $\Pi_\alpha(S)$, (iii) $\Pi_\beta(S)$, and (iv) $\Pi_\lambda(S)$, with the remaining parameters fixed.
• Figure 6: Equation of state $P(v,T)$ for the deformed AdS black hole with fixed $\alpha,\beta,\gamma,\lambda$. The dashed curve corresponds to the critical isotherm. The black dot marks the critical point $(P_c,v_c,T_c) \simeq (0.00201,\,5.337,\,0.0304)$.