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Keywords = wormhole shadow

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30 pages, 2037 KiB  
Article
Probing Modified Gravity Theories with Scalar Fields Using Black-Hole Images
by Georgios Antoniou, Alexandros Papageorgiou and Panagiota Kanti
Universe 2023, 9(3), 147; https://doi.org/10.3390/universe9030147 - 11 Mar 2023
Cited by 11 | Viewed by 2791
Abstract
We study a number of well-motivated theories of modified gravity with the common overarching theme that they predict the existence of compact objects, such as black holes and wormholes endowed with scalar hair. We compute the shadow radius of the resulting compact objects [...] Read more.
We study a number of well-motivated theories of modified gravity with the common overarching theme that they predict the existence of compact objects, such as black holes and wormholes endowed with scalar hair. We compute the shadow radius of the resulting compact objects and demonstrate that black hole images, such as that of M87* or the more recent SgrA* by the Event Horizon Telescope (EHT) collaboration, could provide a powerful way to constrain deviations of the metric functions from what is expected from general relativity (GR) solutions. We focus our attention on Einstein-scalar-Gauss–Bonnet (EsGB) theory with three well-motivated couplings, including the dilatonic and Z2 symmetric cases. We then analyze the shadow radius of black holes in the context of the spontaneous scalarization scenario within EsGB theory with an additional coupling to the Ricci scalar (EsRGB). Finally, we turn our attention to spontaneous scalarization in the Einstein–Maxwell-Scalar (EMS) theory and demonstrate the impact of the parameters on the black hole shadow. Our results show that black hole imaging is an important tool for constraining black holes with scalar hair, and, for some part of the parameter space, black hole solutions with scalar hair may be marginally favored compared to solutions of GR. Full article
(This article belongs to the Section Gravitation)
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12 pages, 333 KiB  
Article
Analogue Metric in a Black-Bounce Background
by Kunal Pal, Kuntal Pal and Tapobrata Sarkar
Universe 2022, 8(4), 197; https://doi.org/10.3390/universe8040197 - 22 Mar 2022
Cited by 4 | Viewed by 2016
Abstract
The conventional approach of embedding an effective acoustic metric for sound motion in a background flat Minkowski space-time has recently been extended to incorporate more general curved background metrics, which might contain a black hole. Though the observational aspects of these kinds of [...] Read more.
The conventional approach of embedding an effective acoustic metric for sound motion in a background flat Minkowski space-time has recently been extended to incorporate more general curved background metrics, which might contain a black hole. Though the observational aspects of these kinds of acoustics horizons, including the sonic shadow structure and quasi normal modes, have received significant attention in the literature, there is room left for discussions about embedding more general classes of curved background space-times without optical horizons. Here, we propose and study a new class of acoustic metrics that is embedded in a black-bounce space-time, thereby giving a suitable tuneable system to understand possible observational effects of the presence or absence of acoustic horizons. After showing that the metric can represent five types of different effective backgrounds for sound motion, including a novel “acoustic wormhole–optical wormhole” branch, we discuss how the distinctive features of sonic shadows can appear even in the absence of any acoustic horizon due to the wormhole throat present in the acoustic metric. Full article
(This article belongs to the Special Issue Analogue Gravity)
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