Testing general relativity with the Event Horizon Telescope

Psaltis, Dimitrios

doi:10.1007/s10714-019-2611-5

Cited by 139 publications

(98 citation statements)

References 172 publications

(201 reference statements)

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“…We upgrade classical black-hole spacetimes by incorporating this scale dependence, assuming that the relevant physical scale is the local curvature scale. Therefore, modifications are largest close to the horizon and thus our work is one example of the general point that the shadow size is a powerful test of gravity [95,120]. In constructing the asymptotic-safety inspired spacetime, we for the first time take into account the angular dependence of the local curvature scale in axisymmetric spacetimes, and add to the evidence that the scale-dependence of the Newton coupling could lead to singularity-resolution.…”

Section: Discussionmentioning

confidence: 93%

“…Due to the no-hair theorem, the mass and spin of the black hole are the only two parameters determining shape and size of the shadow in GR. In this case, the black-hole shadow is nearly circular in shape even for rapidly spinning black holes [120]. In alternative theories of gravity, richer structures are possible [31,32,94].…”

Section: Motivationmentioning

confidence: 92%

“…In contrast, both the origin of the detected gravitational-wave signals as well as the radio-emission detected by the EHT lie in the strong-field regime, where curvature effects become significant. A clear prerequisite for tests of GR based on EHT observations, as advocated in [30,45,61,92,93,95,120,121,152], is the development of model-predictions from modifications of GR, some of which might be of quantum origin. Specifically, the observable we focus on is the shape and size of black-hole shadows, which has become visible in images of horizon-scale structures [38][39][40][41][42][43].…”

Section: Motivationmentioning

confidence: 99%

See 2 more Smart Citations

Asymptotic safety casts its shadow

Held

Gold

Eichhorn

2019

J. Cosmol. Astropart. Phys.

122

138

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We set out to bridge the gap between regular black-hole spacetimes and observations of a black-hole shadow by the Event Horizon Telescope. We explore modifications of spinning and non-spinning black-hole spacetimes inspired by asymptotically safe quantum gravity which features a scale dependence of the Newton coupling. As a consequence, the predictions of our model, such as the shadow shape and size, depend on one free parameter determining the curvature scale at which deviations from General Relativity set in. In more general new-physics settings, it can also depart substantially from the Planck scale. In this case, the free parameter is constrained by observations, since the corresponding curvature scale is significantly below the Planck-scale. The leading new-physics effect can be recast as a scale-dependent black-hole mass, resulting in distinct observational signatures of our model. As a concrete example, we show that two mass-measurements, extracted from the size of the shadow and from Keplerian orbital motion of stars, allow to distinguish the classical from the modified, regular black-hole spacetime, yielding a bound on the free parameter. For spinning black holes, we further find that the singularity-resolving new physics puts a characteristic dent in the shadow. Finally, we argue, based on the underlying physical mechanism, that the effects we derive could be generic consequences of a large class of quantum-gravity theories.

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Section: Discussionmentioning

confidence: 93%

Section: Motivationmentioning

confidence: 92%

Section: Motivationmentioning

confidence: 99%

See 1 more Smart Citation

Asymptotic safety casts its shadow

Held

Gold

Eichhorn

2019

J. Cosmol. Astropart. Phys.

122

138

View full text Add to dashboard Cite

show abstract

“…Let us imagine for instance what would happen if observations conclude that L obs ∼ m and that 1; M l should be then proportional to 2 . This could be compared with other independent determinations of these parameters through observations of the environment of astrophysical black holes, such as the ones that will be carried out by the Event Horizon Telescope [30,31]. Hence, Eqs.…”

Section: Implications and Conclusionmentioning

confidence: 99%

Generalized no-hair theorems without horizons

Barceló

Carballo-Rubio

Liberati

2019

Class. Quantum Grav.

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The simplicity of black holes, as characterized by no-hair theorems, is one of the most important mathematical results in the framework of general relativity. Are these theorems unique to black hole spacetimes, or do they also constrain the geometry around regions of spacetime with arbitrarily large (although finite) redshift? This paper presents a systematic study of this question and illustrates that no-hair theorems are not restricted to spacetimes with event horizons but are instead characteristic of spacetimes with deep enough gravitational wells, extending Israel's theorem to static spacetimes without event horizons that contain small deviations from spherical symmetry.Instead of a uniqueness result, we obtain a theorem that constrains the allowed deviations from the Schwarzschild metric and guarantees that these deviations decrease with the maximum redshift of the gravitational well in the external vacuum region. Israel's theorem is recovered continuously in the limit of infinite redshift. This result provides a first extension of no-hair theorems to ultracompact stars, wormholes, and other exotic objects, and paves the way for the construction of similar results for stationary spacetimes describing rotating objects.

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“…It is exciting that very soon the Event Horizon Telescope (EHT) will provide the first images ever, of horizon size scale observations of the two most studied supermassive black holes Sgr A * [1][2][3] and that in M87 [4]. The accessible information obtained from the observations will reveal the most interesting features of the physics developing near the black hole horizon, including tests of conventional models of matter revolving around the black hole [5], the magnetic fields involved [6], radiation-matter coupling models happening at very strong gravitational fields [7], quantum effects like Hawking radiation processes [8], tests of General Relativity in such strong field scenario [9], among other applications.…”

Section: Introductionmentioning

confidence: 99%

Classification of a black hole spin out of its shadow using support vector machines

González

Guzmán

2019

Phys. Rev. D

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We use Support Vector Machines (SVMs) to classify the spin of a black hole. The SVMs are trained and tested with a catalog of numerically generated images of black holes, assuming disk and spherical matter models with monochromatic emission with wavelength of 4mm. We determine the accuracy of the SVM to classify the spin in terms of the image resolution, for which we consider three resolutions of 16 2 , 32 2 and 64 2 pixels. Our approach is applied to the specific mass of the Supermassive Black Hole (SMBH) at the center of the Milky Way. Our findings are that when the distribution is a thin disk, the accuracy in the classification is acceptable even for the coarsest resolution with accuracy over 90%, whereas for the spherical distribution it drops below 80% for low and intermediate resolutions. The results show how the distribution of matter, the angle of vision and the image resolution influence the difficulty to determine the correct range of black hole spin.

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Testing general relativity with the Event Horizon Telescope

Abstract: The Event Horizon Telescope is a millimeter VLBI array that aims to take the first pictures of the black holes in the center of the Milky Way and of the M87 galaxy, with horizon scale resolution.

Cited by 139 publications

References 172 publications

Asymptotic safety casts its shadow

Asymptotic safety casts its shadow

Generalized no-hair theorems without horizons

Classification of a black hole spin out of its shadow using support vector machines

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