Einstein-Æther gravity in the light of event horizon telescope observations of M87*

Khodadi, Mohsen; Saridakis, Emmanuel N.

doi:10.1016/j.dark.2021.100835

Cited by 65 publications

(11 citation statements)

References 117 publications

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“…In order to describe the shadow as seen by large distances, one introduces the two celestial coordinates X and Y [85], namely X = lim r * →∞ −r 2 * sin θ 0 dφ dr and Y = lim r * →∞ r 2 * dθ dr , with r * the distance between the black hole and the observer, and θ 0 the inclination angle between the observer's line of sight and the black hole rotational axis. Using the geodesics equations we finally obtain [86].…”

Section: Barrow Entropy Effect On Black Hole Shadowsmentioning

confidence: 99%

Constraints on Barrow Entropy from M87* and S2 Star Observations

et al. 2022

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We use data from M87* central black hole shadow, as well as from the S2 star observations, in order to extract constraints on Barrow entropy. The latter is a modified entropy arising from quantum-gravitational effects on the black hole horizon, quantified by the new parameter Δ. Such a change in entropy leads to a change in temperature, as well as to the properties of the black hole and its shadow. We investigate the photon sphere and the shadow of a black hole with Barrow entropy, and assuming a simple model for infalling and radiating gas we estimate the corresponding intensity. Furthermore, we use the radius in order to extract the real part of the quasinormal modes, and for completeness we investigate the spherical accretion of matter onto the black hole, focusing on isothermal and polytropic test fluids. We extract the allowed parameter region, and by applying a Monte-Carlo-Markov Chains analysis we find that Δ≃0.0036−0.0145+0.0792. Hence, our results place the upper bound Δ≲0.0828 at 1σ, a constraint that is less strong than the Big Bang Nucleosynthesis one, but significantly stronger than the late-time cosmological constraints.

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Section: Barrow Entropy Effect On Black Hole Shadowsmentioning

confidence: 99%

Constraints on Barrow Entropy from M87* and S2 Star Observations

et al. 2022

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“…We adopt a rough analysis by using the generalized metric (66). Given that the leading term of the black hole spin parameter is only presence in the nondiagonal component tϕ of the Kerr black hole metric and this component does not deform the photon ring [95], we expect the qualitative conclusions will not be changed if we only focus on the overall size of photon ring. Nevertheless, given that the Eq.…”

Section: B Methods and Resultsmentioning

confidence: 99%

New test on the Einstein equivalence principle through the photon ring of black holes

Zhao

Cai

2021

Phys. Rev. D

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Einstein equivalence principle (EEP), as one of the foundations of general relativity, is a fundamental test of gravity theories. In this paper, we propose a new method to test the EEP of electromagnetic interactions through observations of black hole photon rings, which naturally extends the scale of Newtonian and post-Newtonian gravity where the EEP violation through a variable fine structure constant has been well constrained to that of stronger gravity. We start from a general form of Lagrangian that violates EEP, where a specific EEP violation model could be regarded as one of the cases of this Lagrangian. Within the geometrical optical approximation, we find that the dispersion relation of photons is modified: for photons moving in circular orbit, the dispersion relation simplifies, and behaves such that photons with different linear polarizations perceive different gravitational potentials. This makes the size of black hole photon ring depend on polarization. Further assuming that the EEP violation is small, we derive an approximate analytic expression for spherical black holes showing that the change in size of the photon ring is proportional to the violation parameters. We also discuss several cases of this analytic expression for specific models. Finally, we explore the effects of black hole rotation and derive a modified proportionality relation between the change in size of photon ring and the violation parameters. The numerical and analytic results show that the influence of black hole rotation on the constraints of EEP violation is relatively weak for small magnitude of EEP violation and small rotation speed of black holes.

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“…Recently, the polarization of the ring and magnetic field structure near the horizon was studied based on the first picture of M87* [36,37]. Up to now, black hole shadows have been studied widely [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52].…”

Section: Introductionmentioning

confidence: 99%

Shadow of a nonsingular black hole

Guo¹,

Wei²,

Liu³

2022

Preprint

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Seeking singularity free solutions are important for further understanding black holes in quantum level. Recently, a five-dimensional singularity free topology star/black hole was constructed [Phys. Rev. Lett. 126, 151101 (2021)]. Through the Kaluza-Klein reduction, an effective four-dimensional static spherically symmetric nonsingular black hole can be obtained. In this paper, we study shadow of this nonsingular black hole using three kinds of observers, i.e. static observers, surrounding observers, and freely falling observers, in four-dimensional spacetime. For a spherically symmetric black hole, the shadow is circular for any observer, but the shadow size depends on the motion status of the observer. The shadow size observed by a moving observer will tend to be shrunk. On the other hand, the effect of plasma is also investigated by a simple model. The radius of the photon sphere depends on the plasma model. Most importantly, we find that the shadow sizes do not monotonically decrease with r in some cases. This is a typical phenomenon for this nonsingular black hole.

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Einstein-Æther gravity in the light of event horizon telescope observations of M87*

Cited by 65 publications

References 117 publications

Constraints on Barrow Entropy from M87* and S2 Star Observations

Constraints on Barrow Entropy from M87* and S2 Star Observations

New test on the Einstein equivalence principle through the photon ring of black holes

Shadow of a nonsingular black hole

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