Photon Orbits and Thermodynamic Phase Transition of Regular AdS Black Holes

TL;DR

This paper investigates the connection between photon orbits and thermodynamic phase transitions in regular AdS black holes, revealing that photon orbit parameters serve as indicators of small-large black hole phase changes with critical behavior.

Contribution

It introduces a novel approach linking photon orbit characteristics to thermodynamic phase transitions in regular AdS black holes, highlighting their close relationship.

Findings

Photon orbit radius and impact parameter exhibit non-monotonous behavior near phase transition points.

Differences in photon orbit parameters act as order parameters with a critical exponent of 1/2.

A strong correlation between gravitational dynamics and thermodynamics in regular AdS black holes.

Abstract

We probe the phase structure of the regular AdS black holes using the null geodesics. The radius of photon orbit and minimum impact parameter shows a non-monotonous behaviour below the critical values of the temperature and the pressure, corresponding to the phase transition in extended phase space. The respective differences of the radius of unstable circular orbit and the minimum impact parameter can be seen as the order parameter for the small-large black hole phase transition, with a critical exponent $1/2$. Our study shows that there exists a close relationship between the gravity and thermodynamics for the regular AdS black holes.