Light trajectories and thermal shadows casted by black holes in a cavity

Abstract

We explore the shadows and the photon rings casted by black holes in cavity. Placing the observer inside such an isothermal background, we examine the influence of the cavity temperature T cav and the charge Q on the involved optical features. After studying the effect of the horizon radius by varying Q, we investigate the thermal behaviors of the black hole shadows in a cavity. For fixed charge values, we find that the shadow radius r s increases by decreasing T cav. Varying such a temperature, we discuss the associated energy emission rate. After that, we show that the curves in the r s-T cav plane share similarities with the G-T curves of the Anti de Sitter black holes. Then, we study the trajectories of the light rays casted by black holes in a cavity. We further observe that the light trajectory behaviors are different than the ones of the non rotating black holes due to the cavity effect. Finally, we provide an evidence for the existence of an universal ratio defined in terms of the photon sphere radius and the impact parameter. Concretely, we obtain an optical ratio b sp/r sp∼√(3).