Quasinormal modes, photon orbits and shadow of Kerr–Newman black holes in scalar–tensor–vector gravity

We study the properties of Kerr-Newman black holes (BHs) in scalar-tensor-vector gravity (STVG) and emphasize the effects of rotation, electric charge, and the STVG coupling parameter. We adopt the rotating metric as an effective Kerr-Newman-like STVG ansatz for our analysis. Building on the rotating extension of the STVG solution, we analyze the horizon structure and effective mass, highlighting the roles of frame-dragging and gravitational corrections. We then investigate null geodesics and photon dynamics to determine the photon regions and corresponding BH shadow. Using these results, we compute the shadow radius and distortion and compare them with Event Horizon Telescope (EHT) observations of M87* and Sgr A*, performing qualitative consistency checks on the model parameters. Furthermore, we examine the energy emission rate associated with Hawking radiation and explore how modified gravity affects the emission spectrum. Finally, we study quasinormal modes (QNMs) in the eikonal limit via the photon ring correspondence and discuss their connection with shadow observables. Our results show that STVG introduces measurable deviations from the standard Kerr–Newman geometry, while current observations still favor parameter ranges close to general relativity.

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