Photon sphere and phase transition of d-dimensional (d ≥ 5) charged Gauss-Bonnet AdS black holes

Shan-Zhong Han,Jie Jiang,Ming Zhang,Wen-Biao Liu

Figure 2. (a) Coexistence curve for five-dimensional charged GB-AdS black holes; (b) isobaric curves (blue solid line) with $\tilde{P}=0.9,1.0$ and 1.1 from bottom to top in $\tilde{T}-\tilde{{r}_{p}}$ diagram. Cyan dashed curve denotes the state calculated from the equation of state. Note that in this coexistence region, the equation of sate is invalid. Green (left) and Red (right) dashed curves correspond to saturated small and large black holes. Black dot S and L correspond to saturated small and large black hole for constant pressure $\tilde{P}=0.9$. Orange dot C denotes critical point. rps and rpl denote the photon sphere radius of small and large black holes. Here, we set Q = 1, α = 0.2.