Magnetic Black Holes Research Articles

Thermal stability and phase transitions of static magnetic charged black holes in the background of perfect fluid-type dark matter: Analysis of crucial thermodynamic parameters and P–V criticality along with higher-order entropy corrections

This work focuses on the analysis of P–V criticality for several entropy corrections of uncorrected zeroth entropy of the static magnetic charged black hole embedded in perfect fluid-type dark matter. During the study of P–V criticality, critical points up to several orders are found out. However, the critical points for distinct orders are found to occur at distinct values of the radius of the event horizon. We have resolved the physical significance of those critical points. Further, we have observed that P–V curve wise characteristics do not follow Boyle’s law for some corrections of entropy but it pursues Boyle’s law if we modify the zeroth entropy in some different ways. Physical significance of this phenomenon is also discussed. Again, the heat capacity of the charged black hole for corrected entropies is calculated. Significantly, several phase transitions are observed after plotting those data. We have also investigated how these phase transitions affect the structure of the black hole. Besides, study of free energy and Hawking temperature gives different important cuspidal nodes. The physical significance of these cusps is also discussed. Finally, we obtained an explicit scenario of the phase evolution and stability of the concerned investigated black hole embedded in dark matter.

Corrected thermodynamics and stability of magnetic charged AdS black holes surrounded by quintessence

In this study, we explore the corrected thermodynamics of non-linear magnetic charged anti-de Sitter (AdS) black holes surrounded by quintessence, incorporating thermal fluctuations and deriving the corrected thermodynamic potentials. We analyze the effects of corrections due to thermal fluctuations on various thermodynamic potentials, including enthalpy, Helmholtz free energy, and Gibbs free energy. Our results show significant impacts on smaller black holes, with first-order corrections destabilizing them, while second-order corrections enhance stability with increasing parameter values. The specific heat analysis further elucidates the stability criteria, indicating that the large black holes ensure stability against phase transitions. However, the thermal fluctuations do not affect the physical limitation points as well as the second-order phase transition points of the black hole. Our findings highlight the intricate role of thermal fluctuations in black hole thermodynamics and their influence on stability, providing deeper insights into the behaviour of black holes under corrected thermodynamic conditions.

QPOs from charged particles around magnetized black holes in braneworlds

Quasiperiodic oscillations (QPOs) are a powerful tool for testing gravity theories, probing gravitational and electromagnetic field properties, and obtaining constraints on the black hole and field parameters. This work considers charged particle dynamics near uniformly magnetized black holes in braneworlds. First, we obtain the solution of the Maxwell equation for magnetic fields and calculate the radial and angular magnetic field components. We derive and analyze the effective potential of charged particles for circular orbits and investigate the energy and angular momentum for the circular orbits. We also analyze the combined effects of magnetic interaction and braneworlds on the charged particles’ innermost stable circular orbits (ISCOs). We calculate the angular momentum of charged particles in Keplerian orbits in the presence of an external magnetic field and braneworlds. Also, we investigate frequencies of the particle oscillations along vertical and angular directions. We applied our studies on particle oscillations to the QPO studies in the relativistic precession model. Finally, we obtain constraints on magnetic interaction and braneworld parameters together with the black hole mass and QPO orbits using Monte Carlo Markov Chain (MCMC) simulation in the four-dimensional parameter space for the QPOs observed in the microquasars XTE J1550-564, GRO J1655-40 & GRS 1915-105, and at the center of galaxies M82 and Milky Way.

The heat engine of magnetic black holes in AdS space with rational nonlinear electrodynamics

The heat engine of magnetic black holes in Einstein–AdS gravity coupled to rational nonlinear electrodynamics, as the working substance, is studied. The dynamical negative cosmological constant is considered as a thermodynamic pressure. We investigate the efficiency of black hole heat engines in extended space thermodynamics for rectangle closed path in the P− V plane and the maximally efficient Carnot cycles. The exact efficiency formula that is written in terms of the mass of the black hole is obtained. It was demonstrated that the black hole efficiency decreases when the nonlinear electrodynamics coupling increases and the black hole efficiency increases if the magnetic charge increases. The relation between the efficiency, event horizon radiuses (entropy), and pressure is obtained. We study an efficiency of the holographic heat engine of a cycle in the vicinity of a critical point. Thus, the heat engine of our model can produce work.

Magnetic black holes in 4D Einstein–Gauss–Bonnet massive gravity coupled to nonlinear electrodynamics

We investigated Einstein–Gauss–Bonnet (EGB) 4D massive gravity coupled to nonlinear electrodynamics (NED) in an anti-de Sitter (AdS) background and found an exact magnetically charged black hole solution. The metric function was analyzed for different values of massive gravity parameters. The first law of black hole thermodynamics and generalized Smarr formula were verified, where we treated the cosmological constant as thermodynamic pressure. We defined vacuum polarization as the conjugate to NED parameter. To analyze the local stability of the black hole, we computed specific heat. We investigated the van der Waals-like/re-entrant phase transition of the black holes and estimated the critical points. We observed small black hole (SBH)/large black hole (LBH) and SBH/intermediate black hole (IBH)/LBH phase transitions. The Joule–Thomson coefficient, inversion, and isenthalpic curves were discussed. Finally, the minimum inversion temperature and the corresponding event horizon radius were obtained using numerical techniques.

Center of Mass Energy of Two Charged Particles Around a Magnetic Kerr Black Hole

Center of Mass Energy of Two Charged Particles Around a Magnetic Kerr Black Hole

Thermodynamics of Magnetic Black Holes with Nonlinear Electrodynamics in Extended Phase Space

We study Einstein’s gravity in AdS space coupled to nonlinear electrodynamics. Thermodynamics in extended phase space of magnetically charged black holes is investigated. We compute the metric and mass functions and their asymptotics, showing that black holes may have one or two horizons. The metric function is regular, f(0)=1, and corrections to the Reissner–Nordström solution are in the order of O(r−3) when the Schwarzschild mass is zero. We prove that the first law of black hole thermodynamics and the generalized Smarr relation hold. The magnetic potential and vacuum polarization conjugated to coupling are computed and depicted. We calculate the Gibbs free energy and the heat capacity showing that first-order and second-order phase transitions take place.

Energy extraction via magnetic reconnection in magnetized black holes

The Comisso-Asenjo mechanism is a novel mechanism proposed recently to extract energy from black holes through magnetic reconnection of the surrounding charged plasma, in which the magnetic field plays a crucial role. In this work, we revisit this process by taking into account the backreaction of the magnetic field on the black hole's geometry. We employ the Kerr-Melvin metric to describe the local near-horizon geometry of the magnetized black hole. By analyzing the circular orbits in the equatorial plane, energy extraction conditions, power and efficiency of the energy extraction, we found that while a stronger magnetic field can enhance plasma magnetization and aid energy extraction, its backreaction on the spacetime may hinder the process, with a larger magnetic field posing a greater obstacle. Balancing these effects, an optimal moderate magnetic field strength is found to be most conducive to energy extraction. Moreover, there is a maximum limit to the magnetic field strength associated with the black hole's spin, beyond which circular orbits in the equatorial plane are prohibited, thereby impeding energy extraction in the current scenario.

Thermodynamics of magnetic black holes with rational nonlinear electrodynamics in AdS spacetime and in the background of perfect fluid dark matter

We study magnetic black holes in Einstein’ gravity with negative cosmological constant coupled to rational nonlinear electrodynamics in the background of perfect fluid dark matter (PFDM). The thermodynamics and phase transitions in expanded phase space are investigated. We obtain the black hole metric function, its asymptotic and analyse the horizon radiuses. It was shown that black holes can have one or two horizons. The first law of black hole thermodynamics and Smarr’s relation are proven. We calculate the magnetic potential and conjugates to PFDM parameter and coupling. The specific heat and Gibbs’s free energy are computed and plotted. We evaluate critical specific volumes, critical temperatures and pressures. There are corrections to the critical ratio 3/8 of Van der Waals fluid. The phase transitions and their dependence on the dark matter parameter are analysed. We observe a van der Waals-like behaviour of isotherms, first-order and second-order phase transitions.

On the Role of the Tail Term in Electromagnetic Radiation Reaction

In a recent study devoted to the influence of electromagnetic radiation reaction on the motion of radiating charged particles in magnetized black hole spacetimes the authors claim that the tail term cannot be neglected in the complete DeWitt–Brehme equation, putting into doubt the previous papers where such an approximation was used. Here, we demonstrate by using simple dimensional arguments that such a statement is misleading in many astrophysically relevant situations. In the case of relativistic electrons moving around a stellar-mass black hole, the tail term is ignorable if a magnetic field of at least a few Gauss is present.On the other hand, in different situations, the tail term can be relevant, as demonstrated in the case of orbital widening, where it can even amplify the effect.

Hidden conformal symmetry and Schwinger effect in extremal magnetized Kerr black holes

This paper explores the near-extremal and extremal magnetized Kerr black hole, revealing the Schwinger effect in the absorption cross section at the spacetime's extremal limit. The agreement with CFT2 hints at hidden conformal symmetry. The analysis uncovers SL(2,R)L×SL(2,R)R symmetry for the massless scalar near the black hole, suggesting the Kerr/CFT correspondence for the magnetized Kerr black holes. Cardy formula of the conformal field theory is used to reproduce the black hole entropy in both extremal and near-extremal cases.

Magnetic Black Hole Thermodynamics in an Extended Phase Space with Nonlinear Electrodynamics.

We study Einstein's gravity coupled to nonlinear electrodynamics with two parameters in anti-de Sitter spacetime. Magnetically charged black holes in an extended phase space are investigated. We obtain the mass and metric functions and the asymptotic and corrections to the Reissner-Nordström metric function when the cosmological constant vanishes. The first law of black hole thermodynamics in an extended phase space is formulated and the magnetic potential and the thermodynamic conjugate to the coupling are obtained. We prove the generalized Smarr relation. The heat capacity and the Gibbs free energy are computed and the phase transitions are studied. It is shown that the electric fields of charged objects at the origin and the electrostatic self-energy are finite within the nonlinear electrodynamics proposed.

Pair of dyon production near magnetized dyonic Reissner-Nordstrom black holes* *Supported by LPPM UNPAR

We investigate the phenomenon of pair production of massive scalar particles with magnetic charge near the horizon of a magnetized dyonic Reissner-Nordstrom black hole. The intrinsic symmetry between the electric and magnetic quantities in the Einstein-Maxwell equations suggests that the pair can be generated through Hawking radiation and the Schwinger effect, provided that the Dirac quantization condition is satisfied.

Exact massless scalar quasibound states of the Ernst black hole

In this work, we present a detailed derivation of novel exact massless scalar quasibound state a static magnetized Ernst black hole background. We successfully solve the governing covariant Klein–Gordon equation and discover the exact radial solutions in terms of the Confluent Heun functions. With the exact radial wave solution in hand, applying its polynomial condition leads to the discovery of the quantized energy levels expression that depends on the black hole’s mass M, magnetic field strength B0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_0$$\\end{document} and also the magnetic and main quantum number (mℓ,n).\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(m_\\ell , n).$$\\end{document} A massive scalar field around the black hole has complex valued energy levels while massless particle has purely imaginary energy levels. Further investigation in small black hole limit and zero magnetic field, the massless scalar’s purely imaginary energy expression is recovered. We also discover the equivalence between massless scalar field around an Ernst black hole with massive scalar field around a Schwarzschild black hole. In the last section, the Hawking radiation in investigated and applying the Damour–Ruffini method, the Hawking temperature is obtained out of the radiation distribution function.

Black holes shielded by magnetic fields

Black holes (BHs) formed by collapsing and/or merging of magnetized progenitors, have magnetic fields penetrating the event horizon, and there are several possible scenarios. Thus, the no-hair theorem that assumes the outside medium is a vacuum, is not applicable in this case. Bearing this in mind and considering a Schwarzschild BH of mass M immersed in a uniform magnetic field B, we show that all three frequencies related to the equatorial circular orbit of a test particle become imaginary for the orbits of radii rB>2B−1. It signifies that if a BH is surrounded by a magnetic field of order B∼Rg−1 (where Rg is the gravitational radius of the BH), a test particle could unable to continue its regular geodesic motion from/at r>rB, hence the accretion disk could not be formed, and the motion of other stellar objects around the BH could be absent. As the BHs are generally detected by watching for their effects on nearby stars and gas, a magnetic field of order B∼Rg−1 could be able to shield a BH in such a way that it could remain undetectable. Motivated with this theoretical investigation and considering the sphere (of radius rf) of magnetic influence around an astrophysical BH, we constrain B, above which a magnetized BH could remain undetectable. For example, M=109M⊙ BH surrounded by B>106 G and M=10M⊙ BH surrounded by B>1014 G could remain undetectable for rf∼105Rg. In other words, our result also explains why a detected SMBH has surprisingly weak magnetic field.

Confinement and nonlinear electrodynamics: Asymptotic Schwarzschild charged black hole

While most nonlinear electrodynamics (NED) models tend to Maxwell’s linear theory in the weak field regime, very recently a model of NED has been proposed in the context of heavy quark–antiquark confinement that gives the same limit in the strong field regime. This form of correction to Maxwell’s linear theory is shown to be applicable in such a confined system. In this model, the radial electric field of a point charge is described by E=qr2+ζqr which consists of a Coulomb term plus a term proportional to the NED parameter ζ. Here in this paper, we extend the previous study on the model and accordingly, first, present more on the properties of the model and then introduce the magnetic black hole solution obtained in the gravity coupled minimally to this NED. The solution due to the unique property of the NED is asymptotically Schwarzschild black hole. In addition to the thermodynamics of the black hole, we investigate the circular speed–radius curve of the hypothetical star orbiting the mentioned black hole. It is shown that again due to the correction of Maxwell’s theory in the weak field limit these curves are equivalent to the corresponding curves in the Schwarzschild black hole.

Particle dynamics and shadow of a regular non-minimal magnetic black hole

Particle dynamics and shadow of a regular non-minimal magnetic black hole

Magnetic black holes: From Thomson dipoles to the Penrose process and cosmic censorship

Magnetic black holes: From Thomson dipoles to the Penrose process and cosmic censorship

Einstein-AdS Gravity Coupled to Nonlinear Electrodynamics, Magnetic Black Holes, Thermodynamics in an Extended Phase Space and Joule–Thomson Expansion

We studied Einstein’s gravity with negative cosmological constant coupled to nonlinear electrodynamics proposed earlier. The metric and mass functions and corrections to the Reissner–Nordström solution are obtained. Black hole solutions can have one or two horizons. Thermodynamics and phase transitions of magnetically charged black holes in Anti-de Sitter spacetime are investigated. The first law of black hole thermodynamics is formulated and the generalized Smarr relation is proofed. By calculating the Gibbs free energy and heat capacity we study the black hole stability. Zero-order (reentrant), first-order, and second-order phase transitions are analyzed. The Joule–Thomson expansion is considered, showing the cooling and heating phase transitions. It was shown that the principles of causality and unitarity are satisfied in the model under consideration.

Gravitational capture of magnetic monopoles by primordial black holes in the early universe

It is intriguing to ask whether the existence of primordial black holes (PBHs) in the early universe could significantly reduce the abundance of certain stable massive particles (SMP) via gravitational capture, after which the PBHs evaporate before BBN to avoid conflict with stringent bounds. For example, this mechanism is relevant to an alternative solution of the monopole problem proposed by Stojkovic and Freese, in which magnetic monopoles produced in the early universe are captured by PBHs, thus freeing inflation from having to occur during or after the corresponding phase transitions that produced the monopoles. In this work, we reanalyze the solution by modelling the capture process in the same way as the coexisting monopole annihilation. A subtle issue which is not handled properly in the previous literature is the choice of an effective capture cross section for diffusive capture. We model this aspect properly and justify our treatment. A monochromatic PBH mass function and a radiation-dominated era before PBH evaporation are assumed. We find that for Pati-Salam monopoles corresponding to a symmetry breaking scale between 1010 GeV and 1015 GeV, the capture rate is many orders of magnitude below what is needed to cause a significant reduction of the monopole density. Within our assumptions, we also find that the magnetic charge that is large enough to make an extremal magnetic black hole cosmologically stable cannot be obtained from magnetic charge fluctuation via monopole capture. The large magnetic charged required by cosmological stability can nevertheless be obtained from magnetic charge fluctuation at PBH formation, and if later the monopole abundance can be reduced significantly by some non-inflationary mechanism, long-lived near-extremal magnetic black holes of observational relevance might result.