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Gamma-ray emission in active galaxies is likely produced within the innerjet, or in the close vicinity of the supermassive black hole (SMBH) atsub-parsec distances. Gamma rays have to pass through the surrounding massivestellar cluster which luminous stars can accidentally appear close to theobserver's line of sight. In such a case, soft radiation of massive stars cancreate enough target for transient absorption of the gamma rays in multi-GeV toTeV energy range. We consider the effect of such stellar encounters on thegamma-ray spectrum produced within the massive stellar cluster surrounding acentral SMBH. We predict characteristic, time-dependent effects on thegamma-ray spectra due to the encounter with the single luminous star and alsostellar binary system. We conclude that during the encounter, the gamma-rayspectrum of an active galaxy should steepen at tens of GeV and harden in therange of hundreds of GeV. As an example, we consider such effects on thespectra observed from a typical blazar, 1ES\ 1959+650 (in an active state) andalso in the case of a radio galaxy M87 (in a low state). It is shown thatobservation of such transient characteristic features in the gamma-ray spectra,observed from blazars and radio galaxies, lays within the sensitivity of thefuture Cherenkov Telescope Array.

Absorption effects in the blazar's gamma-ray spectra due to luminous stars crossing the jet