Null Geodesics, Thermodynamics, Weak Gravitational Lensing, and Black Hole Shadow Characteristics of a Frolov Regular Black Hole with Constraints from EHT Observations (2503.19571v1)

Abstract: In this paper, we investigate the properties of null geodesics, thermodynamics, gravitational lensing, and black hole shadows in the vicinity of a static regular Frolov black hole. By analyzing the trajectories of null geodesics, we investigate the bending of light in weak field regimes. The black hole shadow is studied in detail, with constraints on its parameters derived from observational data of the EHT collaboration. Further, we examine shadow images under a spherically symmetric accretion flow and compute the energy emission rate to understand the black hole radiation characteristics. The obtained results demonstrate how the Frolov black hole differs from well-known black hole solutions, such as Schwarzschild, Reissner-Nordstr\"om, and Hayward black holes. This study provides new insights into the impact of modified non-rotating regular black hole metrics on observational signatures. The findings have significant implications for future astrophysical observations and the testing of alternative gravity theories.

Analysis of Null Geodesics, Thermodynamics, Weak Gravitational Lensing, and Black Hole Shadow Characteristics of Frolov Regular Black Holes

The paper of black holes (BHs) continues to yield profound insights into the nature of gravity, spacetime, and fundamental physics. This paper presents an exploration of various properties associated with the Frolov regular black hole, a non-singular solution designed to eliminate the core singularity typically associated with classical black holes. The investigation focuses on several critical aspects: null geodesics, thermodynamics, gravitational lensing, and black hole shadows, with observational constraints provided by the Event Horizon Telescope (EHT).

Geodesics and Horizon Structure

The null geodesic analysis of the Frolov regular black hole reveals deviations from traditional Schwarzschild, Reissner-Nordström (RN), and Hayward black holes. The effective potential associated with these geodesics demonstrates characteristic peaks and troughs, marking potential stable and unstable orbits. In terms of horizon structure, the Frolov metric can support up to two horizons, contingent upon specific values of charge ($q$) and the Hubble length parameter ($\alpha_0$), leading to a diverse range of geometric configurations, including naked singularities beyond certain parameter thresholds.

Thermodynamics

The thermodynamic properties, particularly the Hawking temperature and entropy, underscore the implications of modifying classic black hole metrics. The Hawking temperature is diminished with increasing charge, consistent with the behavior expected in RN solutions. A critical aspect of this paper is the delineation between theoretical and observable thermodynamic laws, correcting traditional equations to accommodate the effects of the metric modifications introduced by $\alpha_0$. Positive heat capacities within specific horizon radii indicate thermodynamic stability, a feature not typically present in standard BH thermodynamics.

Gravitational Lensing and Deflection

The gravitational lensing characteristics of the Frolov black hole further distinguish it from classical models. The deflection angle of light rays, computed using the Gauss-Bonnet theorem in this paper, collectively decreases as the Hubble length parameter increases, suggesting a dampening effect due to cosmic expansion. This phenomenon is mirrored in the computed shadow radius, which displays a shrinking trend when compared to RN and Schwarzschild counterparts as $q$ and $\alpha_0$ intensify.

Shadow Observations

The observationally significant metric of the black hole shadow is intricately examined, with particular focus on its potential constraints derived from EHT data on the Milky Way’s supermassive black hole, Sgr A*. A detailed comparison shows that the shadow size and shape are sensitive indicators of the underlying gravity theory parameters, such as $q$ and $\alpha_0$. Observations of shadow radii challenge the classical no-hair theorem by offering insight into characteristics that these regular black holes possess.

The paper shows that variations in the charge and Hubble length parameters have tangible effects on the shadow radius, consistent with the EHT observations at Sgr A*. The Frolov black hole, due to these distinct observational characteristics, remains a viable candidate for describing astrophysical phenomena amidst a universe where cosmic expansion and electromagnetic charge play significant roles.

Conclusion and Future Directions

This body of research significantly contributes to our understanding of black holes by integrating a non-singular regular solution within observational constraints. The findings hold implications for ongoing and future astrophysical surveys utilizing high-resolution telescopic arrays like the EHT. This work not only enriches the theoretical archive surrounding black holes but also presents observational strategies for constraining the parameters that define and differentiate regular black holes from singular models. Future studies may elaborate on the role of plasma environments and further quantify deviations in geodesic motion to enhance the predictive power of such black hole models in observational astrophysics and alternative gravity theories.