Ali Övgün- Ph.D. in Physics
- Professor (Associate) at Eastern Mediterranean University
Ali Övgün
- Ph.D. in Physics
- Professor (Associate) at Eastern Mediterranean University
Quantum Gravity, Black holes, Cosmology, Wormholes, Gravitational Lensing, Shadow, Quasinormal modes, Greybody factor
About
449
Publications
132,719
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10,652
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Introduction
Current institution
Additional affiliations
August 2018 - July 2020
July 2018 - August 2018
Position
- Research visitor
Description
- PITP 2018 Prospects in Theoretical Physics 2018 From Qubits to Spacetime
April 2018 - May 2018
Education
February 2013 - June 2016
September 2011 - February 2013
September 2010 - June 2011
Publications
Publications (449)
In this paper the deflection angle of light by a rotating Teo wormhole spacetime is calculated in the weak limit approximation. We mainly focus on the weak deflection angle by revealing the gravitational lensing as a partially global topological effect. We apply the Gauss-Bonnet theorem (GBT) to the optical geometry osculating the Teo-Randers wormh...
We present a careful study of accelerating black holes in anti-de Sitter spacetime, formulating the thermodynamics and resolving discrepancies that have appeared in previous investigations of the topic. We compute the dual stress-energy tensor for the spacetime and identify the energy density associated with a static observer at infinity. The dual...
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 General Relativity (GR) BH solutions, and constrain them using the Event Horizon Telescope (EHT) observations o...
Motivated by recent work on the Modified Maxwell (ModMax) black holes [Phys.Lett.B 10.1016/j.physletb.2020.136011], which are invariant in duality rotations and conformal transformations founded in [ Phys.Rev.D 10.1103/PhysRevD.102.121703], we probe its effects on the shadow cast, weak field gravitational lensing, and neutrino propagation in its vi...
Motivated by recent work on the Symmergent black hole [Phys. Dark Univ. 10.1016/j.dark.2021.100900, 2021], here we study spinning black holes in Symmergent gravity, with spin parameter $a$. The goal is to uncover the deviations caused by the Symmergent gravity parameters relative to the known Kerr solution. To this aim, we first investigate the dev...
In this paper, we investigate the gravitational lensing properties of magnetically charged black holes within the framework of nonlinear electrodynamics. We derive the deflection angle and examine the influence of the nonlinear electrodynamics parameter $$\xi $$ ξ on light bending. We initially employ a geometric approach based on the Gauss–Bonnet...
In this paper, we investigate the phenomenology of electrically charged black holes in a Lorentz-violating gravitational framework mediated by a background Kalb-Ramond (KR) antisymmetric tensor field. Employing the Gauss-Bonnet theorem in a non-asymptotically flat geometry, we derive analytic expressions for the weak deflection angle of light and m...
In this study, we investigate traversable wormholes within the framework of Einstein-Euler-Heisenberg (EEH) nonlinear electrodynamics. By employing the Einstein field equations with quantum corrections from the Euler-Heisenberg Lagrangian, we derive wormhole solutions and examine their geometric, physical, and gravitational properties. Two redshift...
In this work, we derive new analytic, static, symmetric black hole solutions in theories involving dark photons with minimal and higher-order magnetic dipole interactions. Starting from the effective non-relativistic potential between fermions mediated by a dark photon, we derive explicit corrections to the Schwarzschild geometry induced by dark ph...
We investigate the influence of the generalized Compton wavelength (GCW), emerging from a three-dimensional dynamical quantum vacuum (3D DQV) on Schwarzschild-like black hole spacetimes, motivated by the work of Fiscaletti [10.1134/S0040577925020096] \cite{Fiscaletti:2025iuh}. The GCW modifies the classical geometry through a deformation parameter...
In this paper, we investigate gravitational collapse scenarios involving baryonic matter transitioning into quark-gluon plasma under extreme astrophysical conditions, focusing on their implications for the formation of regular black holes. Standard gravitational collapse models inevitably predict central singularities, highlighting the limitations...
In this study, we explore a static, spherically symmetric black hole solution in the context of a self-interacting Kalb-Ramond field coupled with a global monopole. By incorporating the effects of Lorentz-violating term $\ell$ and the monopole charge $\eta$ in the KR field, we derive the modified gravitational field equations and analyze the result...
Recent advances, including gravitational wave detections and imaging of black hole shadows, have strongly validated general relativity. Nevertheless, ongoing cosmological observations suggest potential limitations of general relativity, spurring interest in modified theories of gravity. This study explores Lorentz gauge theory, an alternative gravi...
In this paper, we study the influence of the axion-plasmon medium, as proposed in [10.1103/PhysRevLett.120.181803]\cite{Tercas:2018gxv}, on the optical properties of black holes in a Lorentz-violating spacetime containing a global monopole. Our primary aim is to provide a test for detecting the effects of a fixed axion-plasmon background within the...
The standard model of cosmology has provided a good phenomenological description of a wide range of observations both at astrophysical and cosmological scales for several decades. This concordance model is constructed by a universal cosmological constant and supported by a matter sector described by the standard model of particle physics and a cold...
In this study, we investigate traversable wormholes within the framework of Einstein-Euler-Heisenberg (EEH) nonlinear electrodynamics. By employing the Einstein field equations with quantum corrections from the Euler-Heisenberg Lagrangian, we derive wormhole solutions and examine their geometric, physical, and gravitational properties. Two redshift...
This study explores novel static, neutral black hole solutions within Kalb-Ramond (KR) gravity in asymptotically (anti-)de Sitter [(A)dS] spacetimes, incorporating spontaneous Lorentz symmetry breaking via an antisymmetric tensor field. Focusing on two metric configurations, we derive general analytical expressions for the horizon radius, photon sp...
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![Deflection angle ψ1\documentclass[12pt]{minimal} \usepackage{amsmath}...](publication/389702132/figure/fig2/AS:11431281326652121@1743044861995/Deflection-angle-ps1documentclass12ptminimal-usepackageamsmath_Q320.jpg)
In this article, we examine the gravitational deflection of particles in curved spacetime immersed in perfect fluid in the context of Rastall theory. We propose an infinite region approach to Gibbons-Werner to avoid singularity, given that the integral region is generally infinite. In the Rastall theory framework, the black hole solutions in the du...
This work explores both classical and quantum aspects of an axisymmetric black
hole within a non–commutative gauge theory. The rotating solution is derived us-
ing a modified Newman–Janis procedure. The analysis begins with the horizon
structure, ergospheres, and angular velocity. The thermodynamic properties are ex-
amined through surface gravity,...
In this paper, we investigate the gravitational lensing properties of magnetically charged black holes within the framework of nonlinear electrodynamics. We derive the deflection angle and examine the influence of the nonlinear electrodynamics parameter $\xi$ on light bending. Initially, we employ a geometric approach based on the Gauss-Bonnet theo...
We investigate regular black hole formation through the gravitational collapse of baryonic matter characterized by a time- and radius-dependent coefficient of equation of state. Our analysis yields exact solutions to Einstein's field equations that describe singularity-free spacetimes. These solutions are matched to the Husain metric, providing a c...
In this work, we analyze various phenomena influenced by the gravitational field in a bumblebee gravity solution, with a particular emphasis on a traversable wormhole for massless particle modes. Specifically, we calculate the index of refraction, group velocity, time delay, modified distances, and interparticle potential, demonstrating the possibi...
Motivated by the work of Cardoso et al. [Phys. Rev. D 105 (2022) 6, L061501, https://doi.org/10.1103/PhysRevD.105.L061501] on black holes in galaxies, we derive a new black hole solution surrounded by a Dekel-Zhao dark matter profile. The derived metric, influenced by DZ profile parameters, exhibits two distinct regimes: for $r \ll r_{\rm ch}$, exp...
The unification of quantum mechanics and general relativity has long been elusive. Only recently have empirical predictions of various possible theories of quantum gravity been put to test, where a clear signal of quantum properties of gravity is still missing. The dawn of multi-messenger high-energy astrophysics has been tremendously beneficial, a...
In this paper, we present three exact solutions to the Einstein field equations, each illustrating different black hole models. The first solution introduces a black hole with a variable equation of state, P=k(r)ρ, which can represent both singular and regular black holes depending on the parameters M0 and w0. The second solution features a black h...
Inspired by the so-called Palatini formulation of General Relativity and of its modifications and extensions, we consider an analogous formulation of the dynamics of a self-interacting gauge field which is determined by non-linear extension of Maxwell's theory, usually known as nonlinear electrodynamics. In this first order formalism the field stre...
A real astrophysical black hole, surrounded by an accretion disc, experiences time-dependent mass variation due to accretion, impacting observable features like the shadow. In this work, we analyzed the dynamical shadow by extending the concept of the photon sphere to time-dependent spacetimes, incorporating induced, centrifugal, and relativistic f...
This paper explores gravitational phenomena associated with a non-commutative black hole. Geodesic equations are derived, and a thin accretion disk is analyzed to model the black hole shadow image, considering an optically thin, radiating, and infalling gas. Retrolensing effects are examined to trace photon emission configurations, while gravitatio...
This work examines the implications of a black hole featuring a de Sitter core. We begin by analyzing the spacetime and event horizon in the presence of de Sitter core. Then the partial wave equation necessary for calculating quasinormal modes is derived and the relation of scalar quasinormal modes with the de Sitter core parameter is explored. Sub...
This paper links the advanced formulation of the Generalized Uncertainty Principle, termed the Asymptotic Generalized Extended Uncertainty Principle (AGEUP), to the corpuscular framework to derive the AGEUP-inspired black hole metric. The former incorporates spacetime curvature effects to explore black hole dynamics under quantum gravitational corr...
We explored how the Lorentz symmetry breaking parameter ℓ affects the Reissner-Nordstöm BH solution in the context of weak field deflection angle, and the black hole shadow. We aim to derive the general expression for the weak deflection angle using the non-asymptotic version of the Gauss-Bonnet theorem, and we presented a way to simplify the calcu...
Black hole shadows and photon spheres offer valuable tools for investigating black hole properties. Recent observations by the Event Horizon Telescope Collaboration have confirmed the existence of rotating black holes. Black hole parameters influence the observed shadow size. This paper aims to extend the work in [V. Vertogradov and A. Övgün, Analy...
In this work, we start by examining a spherically symmetric black hole within the framework of non-commutative geometry and apply a modified Newman-Janis method to obtain a new rotating solution. We then investigate its consequences, focusing on the horizon structure, ergospheres, and the black hole's angular velocity. Following this, a detailed th...
The paper investigates black hole solutions with a cosmological constant in Einstein-Bumblebee gravity, which incorporates Lorentz symmetry breaking. Focusing on black hole thermodynamics, the study examines modifications to the first law, the equation of state, and critical points, providing insight into black hole behavior in anti-de Sitter (AdS)...
In recent times, the study of the Casimir effect in quantum field theory has garnered increasing attention because of its potential to be an ideal source of exotic matter needed for stabilizing traversable wormholes. It has been confirmed through experimental evidence that this phenomenon involves fluctuations in the vacuum field, leading to a nega...
In this work, we investigate the signatures of black holes within an effective quantum gravity framework recently proposed in the literature [1] . We begin by outlining the general setup, highlighting the two distinct models under consideration. This includes a discussion of their general properties, interpretations, and the structure of the event...
In recent times, the study of the Casimir effect in quantum field theory has garnered increasing attention because of its potential to be an ideal source of exotic matter needed for stabilizing traversable wormholes. It has been confirmed through experimental evidence that this phenomenon involves fluctuations in the vacuum field, leading to a nega...
In this paper, we investigate quasinormal modes (QNMs) and greybody factors within the framework of Symmergent gravity, an emergent gravity model with an $R + R^2$ curvature sector. Building on our previous work on static spherically-symmetric solutions [Class.Quant.Grav. 40 (2023) 19, 195003], we explore the effects of the key parameters, includin...
In this work, we analyze various phenomena influenced by the gravitational field in a bumblebee gravity solution, with a particular emphasis on a traversable wormhole for massless particle modes. Specifically, we calculate the index of refraction, group velocity, time delay, modified distances, and interparticle potential, demonstrating the possibi...
In this paper, we thoroughly explore two crucial aspects of a quantum Schwarzschild black solution within four-dimensional space-time: i) the weak deflection angle, ii) the rigorous greybody factor and, iii) the Dirac quasinormal modes}. Our investigation involves employing the Gauss-Bonnet theorem to precisely compute the deflection angle and esta...
In this paper, we study the thermodynamics of black holes (BHs) that exhibit nontrivial topological characteristics in their phase transition diagrams. We examine D-dimensional dyonic anti-de Sitter BHs within Einstein-Gauss-Bonnet gravity coupled with quasitopological electromagnetism. These BHs feature two types of charges: electric and magnetic....
In this paper, we investigate the properties of relativistic stars made of isotropic matter within the framework of the minimal Standard Model Extension, where a bumblebee field coupled to spacetime induces spontaneous Lorentz symmetry breaking. We adopt analytic equations-of-state describing either condensate dark stars or strange quark stars. We...
In this work, we explore a gravitational non-commutative black hole by gauging the de Sitter SO(4,1) group and employing the Seiberg-Witten map. Specifically, we examine modifications of non-commutativity represented through mass deformation. Initially, we address modifications to Hawking radiation for bosonic particle modes by analyzing the Klein-...
As a way to explore the potential consequences of Lorentz symmetry breaking on gravitational and cosmological phenomena, the Bumblebee model was proposed as a type of modified gravity theory that incorporates spontaneous Lorentz symmetry breaking, achieved by a Bumblebee vector field acquiring a non-zero vacuum expectation value in some preferred d...
In this paper, we present three exact solutions to the Einstein field equations, each showing different black hole models. The first solution introduces a black hole with a variable equation of state, \( P=k(r)\rho \), that can represent both singular and regular black holes based on parameters \( M_0 \) and \( w_0 \). The second solution features...
In this study, we examine the effects of weak gravitational lensing and determine the shadow radius around black holes within the Dyonic ModMax (DM) spacetime, also accounting for models with nonuniform plasma distributions. By analyzing various gravitational lens models, we compare corrections to vacuum lensing due to gravitational effects within...
This study investigates the impact of the quantum-gravity correction at the third-order curvature ($c_6$) on the black hole's shadow and deflection angle on the weak field regime, both involving finite distances of observers. While the calculation of the photonsphere and shadow radius $R_{\rm sh}$ can easily be achieved by the standard Lagrangian f...
The Einstein-Euler-Heisenberg (EEH) black hole model is an extension of classical black hole solutions in general relativity, incorporating quantum electrodynamics (QED) effects via the Euler-Heisenberg Lagrangian. The Euler-Heisenberg Lagrangian describes the nonlinear corrections to Maxwell's equations due to virtual electron-positron pair produc...
In this study, we investigate the signatures of a non-commutative black hole solution. Initially, we calculate the thermodynamic properties of the system, including entropy, heat capacity, and Hawking radiation. For the latter quantity, we employ two distinct methods: surface gravity and the topological approach. Additionally, we examine the emissi...
In this study, we investigate the signatures of a non-commutative black hole solution. Initially, we calculate the thermodynamic properties of the system, including entropy, heat capacity, and Hawking radiation. For the latter quantity, we employ two distinct methods: surface gravity and the topological approach. Additionally, we examine the emissi...
In this study, we investigate the thermodynamic characteristics of the Rindler-Schwarzschild black hole solution. Our analysis encompasses the examination of energy emission, Gibbs free energy, and thermal fluctuations. We calculate various quantities such as the Hawking temperature, geometric mass, and heat capacity to assess the local and global...
This paper investigates the novel phenomenon of gravitational lensing experienced by gravitational waves traveling past a Schwarzschild black hole perturbed by a specific, first-order, polar gravitational wave. We utilize the Gauss-Bonnet theorem, uncovering a topological contribution to the deflection of light rays passing near the black hole. We...
This paper investigates the novel phenomenon of gravitational lensing experienced by gravitational waves traveling past a Schwarzschild black hole perturbed by a specific, first-order, polar gravitational wave. We utilize the Gauss-Bonnet theorem, uncovering a topological contribution to the deflection of light rays passing near the black hole. We...
In this paper we investigate new dyonic black holes of massive gravity sourced by generalized quasitopological electromagnetism in arbitrary dimensions. We begin by deriving the exact solution to the field equations defining these black holes and look at how graviton’s mass, dimensionality parameter, and quasitopological electromagnetic field affec...
Symmergent gravity is an emergent gravity model with an R+R2$R+R^2$ curvature sector and an extended particle sector having new particles beyond the known ones. With constant scalar curvature, asymptotically flat black hole solutions are known to have no sensitivity to the quadratic curvature term (coefficient of R2$R^2$). With variable scalar curv...
We study the tunneling radiation from a charged-accelerating AdS black hole with gauge potential under the impact of quantum gravity. Using the semi-classical phenomenon known as the Hamilton-Jacobi ansatz, it is studied that tunneling radiation occurs via the horizon of a black hole and also employs the Lagrangian equation using the generalised un...
The research presented in this paper discusses the impact that the parameters of charge ( Q ) and screening factor ( γ ) have on properties of the horizon and silhouette of rotating charged ModMax black holes which were reviewed in [ Eur. Phys. J. C (2022) 82:1155] recently, building upon previous findings in the field. Furthermore, the study explo...
In this paper, we obtain a new spherically symmetric black hole surrounded by the pseudo-isothermal dark matter halo. Furthermore, to explore the effects of the pseudo-isothermal halo profile on a rotating black hole at the M87 galactic center, we derive a rotating black hole solution encompassed by the pseudo-isothermal halo by using the Newman-Ja...
Traversable wormholes and regular black holes usually represent completely different scenarios. But in the black bounce spacetime they can be described by a same line element, which is very attractive. Furthermore, the black hole photos taken by EHT show that black holes have spin, so spin is an indispensable intrinsic property of black holes in th...
In this paper, we investigate Schwarzschild-like black holes within the framework of metric-affine bumblebee gravity. We explore the implications of such a gravitational setup on various astrophysical phenomena, including the presence of an accretion disk, the deflection angle of light rays, the establishment of greybody bounds, and the propagation...
Four spherically symmetric but non‐asymptotically flat black hole solutions surrounded with spherical dark matter distribution perceived under the minimal length scale effect is derived via the generalized uncertainty principle. Here, the effect of this quantum correction, described by the parameter γ, is considered on a toy model galaxy with dark...
This work is devoted to discussing spinning particles’ motion in the surrounding dynamic phantom AdS Black hole (BH) with phantom scalar field k. The primary goal of this research is to differentiate between the effects of electric and magnetic charges on dynamic phantom AdS BH. The study analyzes the dependence of the innermost stable circular orb...
In this paper, we investigate a solution for an asymptotic, magnetically-charged, non-singular (AMCNS) black hole. By utilizing the Gauss–Bonnet theorems, we aim to unravel the intricate astrophysics associated with this unique black hole. The study explored various aspects including the black hole’s gravitational field, intrinsic properties, light...
In this paper, we report on exact charged black hole solutions in symmergent gravity with Maxwell field. Symmergent gravity induces the gravitational constant $G$, quadratic curvature coefficient $c_{\rm O}$, and the vacuum energy $V_{\rm O}$ from the flat spacetime matter loops. In the limit in which all fields are degenerate in mass, the vacuum e...
In this paper we investigate new dyonic black holes of massive gravity sourced by generalized quasitopological electromagnetism in arbitrary dimensions. We begin by deriving the exact solution to the field equations defining these black holes and look at how graviton's mass, dimensionality parameter, and quasitopological electromagnetic field affec...
In this paper, we report on exact charged black hole solutions in symmergent gravity with Maxwell field. Symmergent gravity induces the gravitational constant $G$, quadratic curvature coefficient $c_{\rm O}$, and the vacuum energy $V_{\rm O}$ from the flat spacetime matter loops. In the limit in which all fields are degenerate in mass, the vacuum e...
This research focuses on exploring gravitational lensing of the wormhole in Einstein-bumblebee gravity with an antisymmetric tensor. The Gibbons and Werner technique based on the Gauss-Bonnet theorem is utilized to calculate the bending angle of light. The effects of non-plasma and plasma medium on the bending angles are investigated. Furthermore,...
The major goal of this study is to investigate the structure of a thin-shell by matching the inner flat and exterior hairy Schwarzschild black holes using Visser’s approach. Then, by using the equation of motion and the Klein–Gordon equation, we investigate the evolutionary behavior of a thin-shell composed of scalar fields (massive and massless)....
Questions
Questions (21)
Astronomers have uncovered a near-record breaking supermassive black hole, weighing 17 billion suns, in an unlikely place: in the center of a galaxy in a sparsely populated area of the universe. The observations, made by NASA’s Hubble Space Telescope and the Gemini Telescope in Hawaii, may indicate that these monster objects may be more common than once thought.
Has LIGO detected the cross-polarized cylindrical gravitational waves of Einstein and Rosen which is published 28 years ago by M. Halilsoy?
"The researchers, from the University of Cambridge and Queen Mary University of London, have successfully simulated a black hole shaped like a very thin ring, which gives rise to a series of 'bulges' connected by strings that become thinner over time. These strings eventually become so thin that they pinch off into a series of miniature black holes, similar to how a thin stream of water from a tap breaks up into droplets.
Ring-shaped black holes were 'discovered' by theoretical physicists in 2002, but this is the first time that their dynamics have been successfully simulated using supercomputers. Should this type of black hole form, it would lead to the appearance of a 'naked singularity', which would cause the equations behind general relativity to break down. The results are published in the journal Physical Review Letters."
"As long as singularities stay hidden behind an event horizon, they do not cause trouble and general relativity holds - the 'cosmic censorship conjecture' says that this is always the case," said study co-author Markus Kunesch, a PhD student at Cambridge's Department of Applied Mathematics and Theoretical Physics (DAMTP). "As long as the cosmic censorship conjecture is valid, we can safely predict the future outside of black holes. Because ultimately, what we're trying to do in physics is to predict the future given knowledge about the state of the universe now."
But what if a singularity existed outside of an event horizon? If it did, not only would it be visible from the outside, but it would represent an object that has collapsed to an infinite density, a state which causes the laws of physics to break down. Theoretical physicists have hypothesised that such a thing, called a naked singularity, might exist in higher dimensions.
"If naked singularities exist, general relativity breaks down,"
What the Cambridge researchers, along with their co-author Pau Figueras from Queen Mary University of London, have found is that if the ring is thin enough, it can lead to the formation of naked singularities.
