arXiv subjects

Cristian Stelea

Publications and source records attributed to Cristian Stelea.

At least 19 recordsLinked to original sources

arXiv2026

Particle dynamics around an electrically charged Kiselev black hole embedded in quintessence

We introduce and study a new solution describing a static, spherically symmetric and electrically charged black hole embedded in a charged quintessence fluid, which corresponds to an electric generalization of the Kiselev geometry. We derive the effective potential and analyze the various types of orbits followed by charged particles. A special attention is given to circular orbits and their stability. We found that for uncharged particles the periapsis shifts for bounded orbits is always prograde. However, for charged test particles the periapsis shifts can become retrograde in some cases.

gr-qc↗

arXiv2025

Accelerating charged and rotating black holes in scalar multipolar universes

Recently, Cardoso and Natario constructed an exact solution of Einstein-scalar field equations that describes a scalar counterpart of the Schwarzschild-Melvin Universe. In fact, this solution belongs to a more general class of solutions described by Herdeiro in [7]. In this work we show how to further generalize these solutions in presence of acceleration, rotation and various charges. More specifically, we describe general accelerating charged rotating black holes with NUT charge in scalar multipolar universes and present some of their properties.

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arXiv2025

Charged Particles Orbiting a Magnetized Black Hole Immersed in Quintessential Matter

A new exact magnetized solution describing a Kiselev black hole immersed in a magnetic field is used for studying the dynamics of charged particles. Different types of trajectories are discussed. In the particular case of a weak magnetic field, we employ a first-order perturbative approach to analyze the perturbed circular orbits near the minimum of the effective potential. We obtain an approximate solution for the bounded equatorial trajectory subjected to small radial and latitudinal oscillations. The shape of the trajectory localized near the stable circular orbit depends on the relation between the attractive gravitational force and the repulsive quintessence contribution.

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arXiv2024

Charging axially symmetric interior solutions in General Relativity

We present two solution-generating techniques, which are direct generalizations of certain Ehlers-Harrison transformations in the Ernst formalism, while adapted to work in presence of an anisotropic fluid source with axial symmetry. Based on these procedures, we were able to construct the electrically charged and the magnetized solution for any static axially-symmetric geometry, which is sourced in general by an anisotropic fluid described by a non-diagonal anisotropic stress-energy tensor. As our main examples we derived and analyzed two new exact solutions with axial symmetry that describe the electrically charged Zipoy-Vorhees interior solution as well as the magnetized Zipoy-Vorhees interior solution, and presented some of their properties. As further examples of our solution-generating techniques we show how to derive two new solutions describing the electrically charged version of the Bowers and Liang solution, as well as a magnetized version of an exact solution with axial symmetry.

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arXiv2024

Charged black holes with dark halos

Recently, Cardoso et al. constructed an exact solution of Einstein's equations that describes a supermassive black hole immersed into a dark matter halo. In this work use a solution-generating technique, which is a direct generalization of some of the Ehlers-Harrison transformation in the Ehlers formalism in order to construct in an exact analytical form the charged version of the Cardoso et al. solution. We describe some of its physical properties and, finally, we also present its magnetized version.

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arXiv2024

Charged particles in the background of the Kiselev solution in power-Maxwell electrodynamics

In this work we analyze the motion of charged particles in the background of the Kiselev geometry, which is considered here as an exact solution in the context of power-Maxwell electrodynamics. As it is well known, one can use either an electric ansatz or a magnetic one for the nonlinear electromagnetic field. We study the motion of an electrically charged particle for an electrically charged black hole and also for a magnetically charged black hole. In the second case the motion is restricted to Poincaré cones of various angles, as expected.

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arXiv2024

Charged particles moving around a spherically symmetric dilatonic black hole

For the static spherically symmetric dilatonic black hole described by the Gibbons-Maeda-Garfinkle-Horowitz-Strominger geometry, we analyze the timelike trajectories for electrically charged test particles. Both cases of an electric black hole and a magnetic one are considered. Finally, we are obtaining the solution to the Klein--Gordon equation in terms of Heun confluent functions and the corresponding energy spectrum. A special attention is given to the role of the dilaton parameter.

hep-th↗

arXiv2022

The Kiselev solution in power-Maxwell electrodynamics

In this work we reconsider the solution describing black holes surrounded by a `quintessence'-like fluid. This geometry was introduced by Kiselev in 2003 and its physical source was originally modeled by an anisotropic fluid. We show that the Kiselev geometry is actually an exact solution of the Einstein equations coupled to nonlinear electrodynamics. More specifically, we show that the Kiselev geometry becomes an exact solution in the context of power-Maxwell electrodynamics, using either an electric ansatz or a magnetic one. In both cases the physical source can be modeled by a power-Maxwell Lagrangian, albeit with different powers corresponding to the electric or the magnetic charges. We briefly investigate the motion of charged particles in this geometry. Finally, we give the proper interpretation of the black-hole thermodynamics in this context. Similarly to the Schwarzschild-de Sitter case, we note the presence of the Schottky peaks in the heat capacity, signaling out the possibility of this thermodynamic black hole system to function as a continuous heat machine.

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arXiv2022

Probing the Ellis-Bronnikov wormhole geometry with a scalar field: clouds, waves and Q-balls

The Ellis-Bronnikov solution provides a simple toy model for the study of various aspects of wormhole physics. In this work we solve the Klein-Gordon equation in this background and find an exact solution in terms of Heun's function. This may describe 'scalar clouds' ($i.e.$ localized, particle-like configuration) or scalar waves. However, in the former case, the radial derivative of the scalar field is discontinuous at the wormhole's throat (except for the spherical case). This pathology is absent for a suitable scalar field self-interaction, and we provide evidence for the existence of spherically symmetric and spinning Q-balls in a Ellis-Bronnikov wormhole background.

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arXiv2021

Dirac Equation on Kerr--Newman spacetime and Heun functions

By employing a pseudo-orthonormal coordinate-free approach, the Dirac equation for particles in the Kerr--Newman spacetime is separated into its radial and angular parts. In the massless case to which a special attention is given, the general Heun-type equations turn into their confluent form. We show how one recovers some results previously obtained in literature, by other means.

hep-th↗

arXiv2019

Massless fermions on static general prolate metrics and their Heun solutions

Employing a pseudo-orthonormal coordinate-free approach we write down the Dirac equation in spacetimes with static generally prolate metrics. As examples, we consider the electrically charged C-metric, the vacuum C-metric, the Reissner-Nordstrom and Schwarszchild spacetimes and the BBMB black hole and show that the solutions to the Dirac equations for particles these spacetimes can be derived in terms of Heun's general functions and their confluent and double confluent forms.

hep-th↗

arXiv2019

Heun-type solutions of the Klein--Gordon and Dirac equations in the Garfinkle--Horowitz--Strominger dilaton black hole background

We study the Klein-Gordon and the Dirac equations in the background of the Garfinkle-Horowitz-Strominger black hole, in the Einstein frame. Using a $SO(3,1) \times U(1)-$gauge covariant approach, as an alternative to the Newman-Penrose formalism for the Dirac equation, it turns out that these solutions can be expressed in terms of Heun confluent functions and we discuss some of their properties.

hep-th↗

arXiv2018

New bound of the mass-to-radius ratio for electrically charged stars

Using a general solution-generating technique for electrically charged relativistic stars with spherical symmetry, we derive a new bound on the mass-radius ratio. This compactness bound is based on the already established bounds for uncharged interior solutions and it will provide the corresponding generalizations in presence of the electric charge.

gr-qc↗

arXiv2018

On magnetized anisotropic stars

We extend a known solution generating technique for isotropic fluids in order to construct more general models of anisotropic stars with poloidal magnetic fields. In particular, we discuss the magnetized versions of some well-known exact solutions describing anisotropic stars and dark energy stars and we describe some of their properties.

gr-qc↗

arXiv2017

On double-black hole solutions of the Einstein-Maxwell-Dilaton theory in five dimensions

We describe a solution-generating technique that will map a static charged solution of the Einstein-Maxwell theory in four (or five) dimensions to a five-dimensional solution of the Einstein-Maxwell-Dilaton theory. As examples of this technique first we show first how to construct the dilatonic version of the Reissner-Nordström solution in five dimensions and then we consider the more general case of the double black hole solutions and describe some of their properties. We found that in the general case the value of the conical singularities in between the black holes is affected by the dilaton's coupling constant to the gauge field and only in the particular case when all charges are proportional to the masses this dependence cancels out.

gr-qc↗

arXiv2014

Thermodynamics of non-extremal Kaluza-Klein multi-black holes in five dimensions

Using a solution-generating method, we derive an exact solution of the Einstein's field equations in five dimensions describing multi-black hole configurations. More specifically, this solution describes systems of non-extremal static black holes with Kaluza-Klein asymptotics. As expected, we find that, in general, there are conical singularities in-between the Kaluza-Klein black holes that cannot be completely eliminated. Notwithstanding the presence of these conical singularities, such solutions still exhibit interesting thermodynamical properties. By choosing an appropriate set of thermodynamic variables we show that the entropy of these objects still obeys the Bekenstein-Hawking law for spaces with Kaluza-Klein asymptotics. This extends the previously known thermodynamic description of asymptotically flat spaces with conical singularities to general spaces with Kaluza-Klein asymptotics with conical singularities. Finally, we obtain a charged generalization of this multi-black hole solution in the general Einstein-Maxwell-Dilaton theory and show how to recover the extremal multi-black hole solution as a particular case.

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arXiv2013

Charged black holes on Kaluza-Klein bubbles

We construct exact solutions of the Einstein-Maxwell-Dilaton field equations in five dimensions, which describe general configurations of charged and static black holes sitting on a Kaluza-Klein bubble. More specifically we discuss the configurations describing two black holes sitting on a Kaluza-Klein bubble and also the general charged static black Saturn balanced by a Kaluza-Klein bubble. A straightforward extension of the solution generating technique leads to a new solution describing the charged static black Saturn on the Taub-bolt instanton. We compute the conserved charges and investigate some of the thermodynamic properties of these systems.

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arXiv2012

A black ring on the Taub-bolt instanton in five dimensions

Using a solution generating technique, we derive a new exact solution describing a charged static black ring on the Taub-bolt gravitational instanton in five dimensions. Unlike the black ring constructed on the self-dual Taub-NUT instanton, it turns out that it is possible to find values of the parameters for which the static black ring is in equilibrium and the conical singularities disappear. We compute its conserved charges and discuss some of its thermodynamic properties.

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