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Constraints on black-hole charges with the 2017 EHT observations of M87*

Prashant Kocherlakota et al. (EHT Collaboration)
Phys. Rev. D 103, 104047 – Published 20 May 2021
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  • INTRODUCTION
  • SPHERICAL NULL GEODESICS AND SHADOWS
  • SHADOW SIZE CONSTRAINTS FROM THE 2017…
  • NOTABLE PROPERTIES OF VARIOUS SPACETIMES
  • CHARGE CONSTRAINTS FROM THE EHT M87*…
  • CONCLUSIONS
  • ACKNOWLEDGMENTS
  • APPENDICES
    • References

    Abstract

    Our understanding of strong gravity near supermassive compact objects has recently improved thanks to the measurements made by the Event Horizon Telescope (EHT). We use here the M87* shadow size to infer constraints on the physical charges of a large variety of nonrotating or rotating black holes. For example, we show that the quality of the measurements is already sufficient to rule out that M87* is a highly charged dilaton black hole. Similarly, when considering black holes with two physical and independent charges, we are able to exclude considerable regions of the space of parameters for the doubly-charged dilaton and the Sen black holes.

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    • Received 29 November 2020
    • Accepted 21 April 2021

    DOI:https://doi.org/10.1103/PhysRevD.103.104047

    Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

    Published by the American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Alternative gravity theoriesExperimental studies of gravityGeneral relativityRadio, microwave, & sub-mm astronomy
    1. Physical Systems
    Accretion disk & black-hole plasmaClassical black holesGalaxies
    1. Techniques
    Electromagnetic radiation astronomy
    Gravitation, Cosmology & Astrophysics

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    Issue

    Vol. 103, Iss. 10 — 15 May 2021

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    • Figure 1
      Figure 1

      Left: variation in the photon sphere radii for the single-charge nonrotating solutions as a function of the normalized physical charge. Right: The same as in the left panel but for the ISCO radii. We include also, for comparison, the variation in the Kerr equatorial prograde and retrograde photon sphere and ISCO radii in the left and right panels respectively.

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    • Figure 2
      Figure 2

      Left: shadow radii r˜sh for various spherically symmetric black-hole solutions, as well as for the JNW and RN naked singularities (marked with an asterisk), as a function of the physical charge normalized to its maximum value. The gray/red shaded regions refer to the areas that are 1−σ consistent/inconsistent with the 2017 EHT observations and highlight that the latter set constraints on the physical charges (see also Fig. 3 for the EMd-2 black hole). Right: shadow areal radii rsh,A as a function of the dimensionless spin a for four families of black-hole solutions when viewed on the equatorial plane (i=π/2). Also in this case, the observations restrict the ranges of the physical charges of the Kerr-Newman and the Sen black holes (see also Fig. 3).

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    • Figure 3
      Figure 3

      Constraints set by the 2017 EHT observations on the nonrotating Einstein-Maxwell-dilaton 2 and on the rotating Sen black holes. Also in this case, the gray/red shaded regions refer to the areas that are 1−σ consistent/inconsistent with the 2017 EHT observations).

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    • Figure 4
      Figure 4

      Distortion parameter δsh for a number of stationary black holes observed on the equatorial plane (i=π/2) with dimensionless spin a. Because for observers viewing the black hole from inclinations increasingly close to the pole, the shadow boundary appears increasingly circular, the distortions reported can be taken as upper limits.

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