Abstract:
We probe the phase structure of the regular anti–de Sitter (AdS) black holes using the null geodesics. The
radius of photon orbit and minimum impact parameter shows a nonmonotonous behavior 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.
