[Submitted on 31 Oct 2022]

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

    Submission history

    From: Georgios Antoniou [view email]

    Mon, 31 Oct 2022 17:49:14 UTC (1,604 KB)

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