Gravastar: An alternative to black hole

In this work, we review thoroughly the origin, development and present status of gravastar which has been thought to be an alternative to black hole along with its future feasibility in the sense of astrophysical observation. The Mazur–Mottola model of the gravastar is introduced first followed by a review of its generalizations within the context of general relativity including physical applications like primordial and cylindrical gravastars. The study of gravastar in higher- and lower-dimensional general relativity (GR) including the higher-dimensional theories with physical insight like the Randall–Sundrum model is presented. The gravastar models in a number of modified gravity models starting from [Formula: see text] to Rastall–Rainbow gravity have been reviewed.

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Observing the shadow of modified gravity black hole

International Journal of Modern Physics D ◽

10.1142/s0218271817501565 ◽

2017 ◽

Vol 26 (14) ◽

pp. 1750156 ◽

Cited By ~ 2

Author(s):

Ahmed Alhamzawi

Keyword(s):

Black Holes ◽

Black Hole ◽

Modified Gravity ◽

Kerr Black Hole ◽

Naked Singularity ◽

Gravity Models ◽

Considerable Contribution ◽

Rotating Black Holes ◽

Shadow Cast ◽

Modified Gravity Models

A study of the shadow cast by rotating black holes in different models of modified gravity is presented. It is shown that the size of the shadow cast depends on the modified gravity model used. The distortions of the shadow cast by modified gravity black holes are investigated and the effects are compared with the distortions cast by Kerr black hole. The shadow of a rotating black hole in modified gravity is found to be similar to the shadow cast by Kerr black hole but with different sizes and distortion effects. The naked singularity by rotating modified gravity black hole is discussed. Finally, it is shown that some modified gravity models can present a considerable contribution to the size of black hole shadow.

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Cosmological test of gravity using weak lensing voids

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2933 ◽

2019 ◽

Vol 490 (4) ◽

pp. 4907-4917 ◽

Cited By ~ 5

Author(s):

Christopher T Davies ◽

Marius Cautun ◽

Baojiu Li

Keyword(s):

General Relativity ◽

Modified Gravity ◽

Matter Field ◽

Gravity Models ◽

Weak Lensing ◽

Signal To Noise ◽

Alternative Approach ◽

Tests Of Gravity ◽

Modified Gravity Models ◽

Better Than

ABSTRACT Modifications to general relativity often incorporate screening mechanisms in order to remain compatible with existing tests of gravity. The screening is less efficient in underdense regions, which suggests that cosmic voids can be a useful cosmological probe for constraining modified gravity models. In particular, weak lensing by voids has been proposed as a promising test of such theories. Usually, voids are identified from galaxy distributions, making them biased tracers of the underlying matter field. An alternative approach is to study voids identified in weak lensing maps – weak lensing voids – which have been shown to better correspond to true underdense regions. In this paper, we study the ability of weak lensing voids to detect the signatures of modified gravity. Focusing on the void abundance and weak lensing profiles, we find that both statistics are sensitive probes of gravity. These are quantified in terms of the signal-to-noise ratios (SNR) with which an LSST-like survey will be able to distinguish between different gravity models. We find that the tangential shear profiles of weak lensing voids are considerably better than galaxy voids at this, though voids have somewhat lower SNR than weak lensing peaks. The abundances of voids and peaks have, respectively, $\rm {SNR} = 50$ and 70 for a popular class of modified gravity in an LSST-like survey.

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Black hole entropy in modified-gravity models

Physical Review D ◽

10.1103/physrevd.77.044009 ◽

2008 ◽

Vol 77 (4) ◽

Cited By ~ 53

Author(s):

F. Briscese ◽

E. Elizalde

Keyword(s):

Black Hole ◽

Modified Gravity ◽

Black Hole Entropy ◽

Gravity Models ◽

Modified Gravity Models

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Dwarf galaxies without dark matter: constraints on modified gravity

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3653 ◽

2020 ◽

Vol 501 (1) ◽

pp. 254-260

Author(s):

Ali Rida Khalifeh ◽

Raul Jimenez

Keyword(s):

Dark Matter ◽

Modified Gravity ◽

Virial Theorem ◽

Dwarf Galaxies ◽

Strong Support ◽

Gravity Models ◽

Birkhoff Theorem ◽

Astronomical Surveys ◽

Stringent Test ◽

Modified Gravity Models

ABSTRACT The discovery of 19 dwarf galaxies without dark matter (DM) provides, counterintuitively, strong support for the ΛCDM standard model of cosmology. Their presence is well accommodated in a scenario where the DM is in the form of cold dark particles. However, it is interesting to explore quantitatively what is needed from modified gravity models to accommodate the presence of these galaxies and what extra degree of freedom is needed in these models. To this end, we derive the dynamics at galaxy scales (Virial theorem) for a general class of modified gravity models. We distinguish between theories that satisfy the Jebsen–Birkhoff theorem, and those that do not. Our aim is to develop tests that can distinguish whether DM is part of the theory of gravity or a particle. The 19 dwarf galaxies discovered provide us with a stringent test for models of modified gravity. Our main finding is that there will always be an extra contribution to the Virial theorem coming from the modification of gravity, even if a certain galaxy shows very small, if not negligible, trace of DM, as has been reported recently. Thus, if these and more galaxies are confirmed as devoid (or negligible) of DM, while other similar galaxies have abundant DM, it seems interesting to find modifications of gravity to describe DM. Our result can be used by future astronomical surveys to put constraints on the parameters of modified gravity models at astrophysical scales where DM is described as such.

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