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We investigate Einstein-\AE ther gravity in light of the recent Event Horizon Telescope (EHT) observations of the M87*. The shape and size of the observed black hole shadow contains information of the geometry in its vicinity, and thus one…

General Relativity and Quantum Cosmology · Physics 2021-05-20 Mohsen Khodadi , Emmanuel N. Saridakis

A key obstacle for theory-specific tests of general relativity is the lack of accurate black-hole solutions in beyond-Einstein theories, especially for moderate to high spins. We address this by developing a general framework--based on…

General Relativity and Quantum Cosmology · Physics 2026-01-19 Kelvin Ka-Ho Lam , Adrian Ka-Wai Chung , Nicolás Yunes

Horizon-scale images of black holes (BHs) and their shadows have opened an unprecedented window onto tests of gravity and fundamental physics in the strong-field regime. We consider a wide range of well-motivated deviations from classical…

Our Galactic Center, Sagittarius A* (Sgr A*), is believed to harbour a supermassive black hole (BH), as suggested by observations tracking individual orbiting stars. Upcoming sub-millimetre very-long-baseline-interferometry (VLBI) images of…

Astrophysical black holes (BHs) are universally expected to be described by the Kerr metric, a stationary, vacuum solution of general relativity (GR). Indeed, by imaging M87$^\star$ and Sgr A$^\star$ and measuring the size of their shadows,…

General Relativity and Quantum Cosmology · Physics 2024-03-07 Prashant Kocherlakota , Luciano Rezzolla , Rittick Roy , Maciek Wielgus

The Event Horizon Telescope (EHT) collaboration unveiled event-horizon-scale images of the supermassive black holes (SMBHs) M87* and Sgr A*, revealing a dark brightness depression, namely the black hole shadow, whose shape and size may…

General Relativity and Quantum Cosmology · Physics 2023-07-27 Misba Afrin , Sushant G. Ghosh

The Event Horizon Telescope (EHT) has imaged the shadow of the supermassive black hole in M87. A library of general relativistic magnetohydrodynamics (GMRHD) models was fit to the observational data, providing constraints on black hole…

High Energy Astrophysical Phenomena · Physics 2021-06-09 Freek Roelofs , Christian M. Fromm , Yosuke Mizuno , Jordy Davelaar , Michael Janssen , Ziri Younsi , Luciano Rezzolla , Heino Falcke

Rapidly rotating black hole solutions in theories beyond general relativity play a key role in experimental gravity, as they allow us to compute observables in extreme spacetimes that deviate from the predictions of general relativity. Such…

General Relativity and Quantum Cosmology · Physics 2016-11-29 Robert McNees , Leo C. Stein , Nicolás Yunes

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 $…

General Relativity and Quantum Cosmology · Physics 2020-05-12 Rahul Kumar , Sushant G. Ghosh

Observations of black hole shadows with the Event Horizon Telescope have paved way for a novel approach to testing Einstein's theory of general relativity. Early analyses of the measured shadow put constraints on theory-agnostic parameters…

General Relativity and Quantum Cosmology · Physics 2021-08-04 Sourabh Nampalliwar , Saurabh K

Recently, two of us have found a family of singularity-free rotating black hole solutions in Einstein's conformal gravity. These spacetimes are characterized by three parameters: the black hole mass $M$, the black hole spin angular momentum…

General Relativity and Quantum Cosmology · Physics 2018-07-06 Menglei Zhou , Zheng Cao , Askar Abdikamalov , Dimitry Ayzenberg , Cosimo Bambi , Leonardo Modesto , Sourabh Nampalliwar

The Event Horizon Telescope (EHT) has provided a new tool for testing the strong-field regime of gravity by imaging the shadows of M87* and Sgr A*. These observations provide the first real opportunity to test whether quantum…

General Relativity and Quantum Cosmology · Physics 2026-05-29 Heena Ali , Sushant G. Ghosh

A mathematically consistent rotating black hole model in loop quantum gravity (LQG) is yet lacking. The scarcity of rotating black hole solutions in LQG substantially hampers the development of testing LQG from observations, e.g., from the…

General Relativity and Quantum Cosmology · Physics 2023-01-25 Shafqat Ul Islam , Jitendra Kumar , Rahul Kumar Walia , Sushant G. Ghosh

Recently, new exploratory channels have opened up for the physics of highly compact objects, such as gravitational waves and black hole shadows. Moreover, more precise analysis and observations are now possible in the physics of accretion…

General Relativity and Quantum Cosmology · Physics 2024-10-01 D. Pugliese , H. Quevedo

The horizon-scale images of supermassive black holes (BHs) by the Event Horizon Telescope Collaboration (EHT) have provided new opportunities to test general relativity and other theories of gravity. In view of future projects, such as the…

General Relativity and Quantum Cosmology · Physics 2025-11-12 Akhil Uniyal , Indu K. Dihingia , Yosuke Mizuno , Luciano Rezzolla

Astrophysical black holes are expected to be described by the Kerr metric. This is the only stationary, vacuum, axisymmetric metric, without electromagnetic charge, that satisfies Einstein's equations and does not have pathologies outside…

High Energy Astrophysical Phenomena · Physics 2023-11-17 The Event Horizon Telescope Collaboration

Black hole (BH) shadow observations and gravitational wave astronomy have become crucial approaches for exploring BH physics and testing gravitational theories in extreme environments. This paper investigates the charged black hole with…

General Relativity and Quantum Cosmology · Physics 2025-09-16 Lai Zhao , Meirong Tang , Zhaoyi Xu

The M87* black hole shadow observation by the Event Horizon Telescope (EHT) has enabled us to test the modified gravity theories in the extreme-field regime and estimating the black hole parameters. Having this assertion, we investigate the…

General Relativity and Quantum Cosmology · Physics 2023-02-06 Sushant G. Ghosh , Rahul Kumar Walia

Searching for violations of the no-hair theorem (NHT) is a powerful way to test gravity, and more generally fundamental physics, particularly with regards to the existence of additional scalar fields. The first observation of a black hole…

General Relativity and Quantum Cosmology · Physics 2020-09-15 Mohsen Khodadi , Alireza Allahyari , Sunny Vagnozzi , David F. Mota

We investigate the astrophysical consequences of black holes in quadratic gravity, characterized by the parameters $S_0$, $S_2$, $m_0$ and $m_2$, in addition to the black hole mass $M$. To evaluate the physical validity of the fundamental…

General Relativity and Quantum Cosmology · Physics 2024-12-24 Somi Aktar , Niyaz Uddin Molla , Farook Rahaman , G. Mustafa
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