Probing Modified Gravity Theories with Scalar Fields Using Black-Hole Images

We study a number of well-motivated theories modified gravity with the common overarching theme that they predict existence compact objects such as black holes and wormholes endowed scalar hair. compute shadow radius resulting demonstrate hole images M87$^*$ or more recent SgrA$^*$ by Einstein Horizon Telescope (EHT) collaboration may provide powerful way to constrain deviations metric functions from what is expected general relativity (GR) solutions. focus our attention on Einstein-scalar-Gauss-Bonnet (EsGB) theory three well motivated couplings, including dilatonic $Z_2$ symmetric cases. then analyze in contest spontaneous scalarization scenario within EsGB an additional coupling Ricci (EsRGB). Finally, we turn Einstein-Maxwell-Scalar (EMS) impact parameters shadow. Our results show imaging important tool for constraining hair some part parameter space, solutions be marginally favoured compared GR.