Corotating point sources on accretion disks near black holes distort the relative magnification factor distribution, modulating caustics and encoding accretion flow kinematics via time-delayed images.
Black Hole Parameter Estimation from Its Shadow
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abstract
The Event Horizon Telescope (EHT), a global submillimeter wavelength very long baseline interferometry array, unveiled event-horizon-scale images of the supermassive black hole M87* as an asymmetric bright emission ring with a diameter of $ 42 \pm 3\; \mu$as, and it is consistent with the shadow of a Kerr black hole of general relativity. A Kerr black hole is also a solution of some alternative theories of gravity, while several modified theories of gravity admit non-Kerr black holes. While earlier estimates for the M87* black hole mass, depending on the method used, fall in the range $ \approx 3\times 10^9 M_\odot- 7 \times 10^9 $$ M_\odot $, the EHT data indicated a mass for the M87* black hole of $(6.5 \pm 0.7) \times 10^9 M_\odot $. This offers another promising tool to estimate black hole parameters and to probe theories of gravity in its most extreme region near the event horizon. The important question arises: Is it possible by a simple technique to estimate black hole parameters from its shadow, for arbitrary models? In this paper, we present observables, expressed in terms of ordinary integrals, characterizing a haphazard shadow shape to estimate the parameters associated with black holes, and then illustrate its relevance to four different models: Kerr, Kerr$-$Newman, and two rotating regular models. Our method is robust, accurate, and consistent with the results obtained from existing formalism, and it is applicable to more general shadow shapes that may not be circular due to noisy data.
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gr-qc 4years
2026 4roles
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Charge most strongly controls JT inversion and cooling domains of the f(R,T)-NLED AdS black hole; NLED and modified-gravity parameters supply only sub-leading corrections that leave exterior geodesics close to RN-AdS.
A diffeomorphic inversion re-parameterizes Kerr, Kerr-MOG, and Horndeski black hole observables in terms of the shadow radius, yielding model-specific deflection and luminosity scalings that break mass degeneracy.
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*.
citing papers explorer
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Relative Magnification Factor of Point Sources on Accretion Disks
Corotating point sources on accretion disks near black holes distort the relative magnification factor distribution, modulating caustics and encoding accretion flow kinematics via time-delayed images.
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Joule-Thomson Effect and Geodesic Structure of Charged AdS Black Holes in f(R,T) Coupled with Nonlinear Electrodynamics
Charge most strongly controls JT inversion and cooling domains of the f(R,T)-NLED AdS black hole; NLED and modified-gravity parameters supply only sub-leading corrections that leave exterior geodesics close to RN-AdS.
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Shadow dependent phenomenology framework for rotating black hole metric
A diffeomorphic inversion re-parameterizes Kerr, Kerr-MOG, and Horndeski black hole observables in terms of the shadow radius, yielding model-specific deflection and luminosity scalings that break mass degeneracy.
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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*.