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 theobserver inside such an isothermal background, we examine the influence of the cavitytemperature T cav and the charge Q on the involved optical features. Afterstudying the effect of the horizon radius by varying Q, we investigate the thermalbehaviors of the black hole shadows in a cavity. For fixed charge values, we find that theshadow radius r s increases by decreasing T cav. Varying such a temperature, wediscuss 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 blackholes. 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 thenon rotating black holes due to the cavity effect. Finally, we provide an evidence for theexistence of an universal ratio defined in terms of the photon sphere radius and the impactparameter. Concretely, we obtain an optical ratio b sp/r sp∼√(3).