Three distinct non-minimal curvature-EM couplings produce different enlargements or reductions of black hole shadows and alter photon ring separations in characteristic ways.
Shadow of rotating regular black holes
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abstract
We study the shadows cast by the different types of rotating regular black holes viz. Ay\'on-Beato-Garc\'ia {(ABG)}, Hayward, and Bardeen. These black holes have in addition to the total mass ($M$) and rotation parameter ($a$), different parameters as electric charge ($Q$), deviation parameter ($g$), and magnetic charge ($g_{*}$), respectively. Interestingly, the size of the shadow is affected by these parameters in addition to the rotation parameter. We found that the radius of the shadow in each case decreases monotonically and the distortion parameter increases when the value of these parameters increase. A comparison with the standard Kerr case is also investigated. We have also studied the influence of the plasma environment around regular black holes to discuss its shadow. The presence of the plasma affects the apparent size of the regular black hole's shadow to be increased due to two effects (i) gravitational redshift of the photons and (ii) radial dependence of plasma density.
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Combining regular black hole metrics with memory burden suppresses evaporation and opens a 10^6-10^8 g PBH mass window that can comprise all dark matter.
Rotating Ayón-Beato-García black holes produce smaller and sometimes D-shaped shadows whose size constrains the charge parameter ζ to the range 0.132811M–0.213607M when matched to EHT observations of M87* and Sgr A*.
EHT shadow observations constrain the Lorentz-violating parameter ℓ in Kalb-Ramond gravity for charged rotating black holes to roughly |ℓ| ≲ 0.1-0.2, with an upper bound ℓ ≲ 0.19 from Sgr A*.
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Photon rings and shadows of black holes with non-minimal couplings between curvature and electromagnetic field
Three distinct non-minimal curvature-EM couplings produce different enlargements or reductions of black hole shadows and alter photon ring separations in characteristic ways.
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Probing Kalb-Ramond gravity with charged rotating black holes: constraints from EHT observations
EHT shadow observations constrain the Lorentz-violating parameter ℓ in Kalb-Ramond gravity for charged rotating black holes to roughly |ℓ| ≲ 0.1-0.2, with an upper bound ℓ ≲ 0.19 from Sgr A*.
- Breaking Parameter Degeneracies in a Magnetically Charged Black Hole Embedded in a Hernquist Dark-Matter Halo: A Multi-Observable Analysis