Schwarzschild Black Hole Case Research Articles

Accretion disks properties around regular black hole solutions obtained from non-linear electrodynamics

We investigate a family of spherically symmetric, static, charged regular black hole solutions derived within the framework of Einstein-nonlinear electrodynamics. Our study focuses on examining the characteristics of accretion disks in the spacetimes described by the Dymnikova and Fan-Wang solutions. We explore circular geodesics of test particles and calculate various properties, including the radius of the innermost stable circular orbit, radiant energy, temperature, and conversion efficiency of accretion mass into radiation. We employ the Novikov-Thorne-Page thin accretion disk model as a background. By comparing our findings with those obtained in the Schwarzschild black hole case, we reveal significant modifications in the overall spectral properties. Specifically, we observe an increase in the energy emitted from the disk surface, resulting in higher temperatures for the accretion disks under certain values of the free parameters. Consequently, we note an enhanced efficiency of mass conversion into radiation compared to the Schwarzschild spacetime.

Particle motion and lensing with plasma of acoustic Schwarzschild black hole

This paper is motivationally based on the study revealing the characteristics of Acoustic Schwarzschild BHs in respect of particle dynamics, and weak gravitational plasma lensing. We discuss the particle dynamics by studying the effective potential, ISCO, for massive particle and photon motion. We consider the weak gravitation field to study the gravitational lensed photons. This purpose of lensing is served by taking under consideration three fields of plasma uniform plasma, singular isothermal sphere and a nonsingular isothermal sphere. Each field is separately incorporated to calculate the plasma deflection angle, which is further utilized in the image magnification associated with the source brightness for uniform plasma and singular isothermal sphere as a selective case. All the obtained results are compared with the Schwarzschild black hole case as a standard.

Shadows and gravitational weak lensing by the Schwarzschild black hole in the string cloud background with quintessential field* *G. Mustafa acknowledges the Grant No. ZC304022919 to support his Postdoctoral Fellowship at Zhejiang Normal University. F.A. acknowledges the support of Inha University in Tashkent and research work has been supported by the Visitor Research Fellowship at Zhejiang Normal University. This research

In this study, we observe that, in the presence of the string cloud parameter a and the quintessence parameter γ, with the equation of state parameter , the radius of the shadow of the Schwarzschild black hole increases as compared with that in the pure Schwarzschild black hole case. The existence of both quintessential dark energy and the cloud of strings increases the shadow size; hence, the strength of the gravitational field around the Schwarzschild black hole increases. Using the data collected by the Event Horizon Telescope (EHT) collaboration for M87* and Sgr A*, we obtain upper bounds on the values of a and γ. Further, we see the effects of a and γ on the rate of emission energy for the Schwarzschild black hole. We notice that the rate of emission energy is higher in the presence of clouds of strings and quintessence. Moreover, we study the weak deflection angle using the Gauss-Bonnet theorem. We show the influence of a and γ on the weak deflection angle. We notice that both a and γ increase the deflection angle α.

Entanglement at the soft-hair horizon

We study entanglement between two modes of a free bosonic and fermionic field as seen by two relatively accelerating observers at the soft-hair horizon of a four-dimensional supertranslated Schwarzschild black hole. First, we associate the shock wave to the near horizon geometry by explicit construction of map between their metric as well as relation between wave form factor and soft hair function. We then compute mutual information and entanglement negativity as a measure of entanglement between these two observers and show that their angular dependence at the soft-hair horizon. We also show that for vanishing soft hair function our results are equal to that of an ordinary Schwarzschild black hole case.

Thin accretion disk in the Simpson-Visser black-bounce and wormhole spacetimes

We compare the optical appearance of a thin accretion disk in the Simpson-Visser spacetime to the Schwarzschild black hole case in this paper. We calculate and illustrate the red-shift and observed flux distributions as viewed by distant observers at various inclination angles. Simpson-Visser family of metrics create Novikov-Thorne (NT) accretion disks images that nearly look like a Schwarzschild black hole's NT accretion disk. We have studied also the embedding diagram, the electromagnetic properties of the accretion disk such as the temperature and the radiation flux of the energy by the accretion disk and the accretion efficiency. Compared to the Schwarzschild black hole, we find that the temperature, radiation flux of the energy, and the luminosity of the accretion disk increase by increasing the regularization parameter $'l'$. We conclude that, based on astrophysical observational signatures in the properties of the electromagnetic spectrum, we can distinguish the wormhole geometries from the regular black holes (black-bounce) and the Schwarzschild black hole.

Pseudospectrum and Black Hole Quasinormal Mode Instability

We study the stability of quasinormal modes (QNM) in asymptotically flat black hole spacetimes by means of a pseudospectrum analysis. The construction of the Schwarzschild QNM pseudospectrum reveals the following: (i) the stability of the slowest-decaying QNM under perturbations respecting the asymptotic structure, reassessing the instability of the fundamental QNM discussed by Nollert [H. P. Nollert, About the Significance of Quasinormal Modes of Black Holes, Phys. Rev. D 53, 4397 (1996)] as an "infrared" effect; (ii) the instability of all overtones under small-scale ("ultraviolet") perturbations of sufficiently high frequency, which migrate towards universal QNM branches along pseudospectra boundaries, shedding light on Nollert's pioneer work and Nollert and Price's analysis [H. P. Nollert and R. H. Price, Quantifying Excitations of Quasinormal Mode Systems, J. Math. Phys. (N.Y.) 40, 980 (1999)]. Methodologically, a compactified hyperboloidal approach to QNMs is adopted to cast QNMs in terms of the spectral problem of a non-self-adjoint operator. In this setting, spectral (in)stability is naturally addressed through the pseudospectrum notion that we construct numerically via Chebyshev spectral methods and foster in gravitational physics. After illustrating the approach with the P\"oschl-Teller potential, we address the Schwarzschild black hole case, where QNM (in)stabilities are physically relevant in the context of black hole spectroscopy in gravitational-wave physics and, conceivably, as probes into fundamental high-frequency spacetime fluctuations at the Planck scale.

Accretion disks around naked singularities

We investigate here the thermal properties of accretion disks in a spacetime for some galactic density profiles in spherical symmetry. The matter distributions have a finite outer radius with a naked central singularity. The luminosities of the accretion disks for some density profile models are found to be higher than those for a Schwarzschild black hole of the same mass. The slopes for the luminosity distributions with respect to frequencies are significantly different, especially at higher frequencies, from that in the Schwarzschild black hole case. Such features may be used to distinguish black holes from naked singularities. The efficiencies for the conversion of mass energy of the accreting gas into radiation and the strength of naked singularities are analyzed. The novel feature that we find is, the strength of the singularity is different depending on the profiles considered, and the stronger the singularity is, the higher is the efficiency for the accretion disk.

Shadows around the q-metric

One crucial problem in relativistic astrophysics is that of the nature of black hole candidates. It is usually assumed that astrophysical black holes are described by the Schwarzschild or Kerr space–times; however, there is no direct evidence to assert this. Moreover, there are various solutions in general relativity that can be alternatives to black holes, usually called black hole mimickers. In this work, we study the shadow produced by a compact object described by the q-metric, which is the simplest static and axially symmetric solution of Einstein equations with a non-vanishing quadrupole moment. This particular space–time has the property of containing an independent parameter q, which is related to the compact object deformation. The solution corresponds to naked singularities for some specific values of this parameter. Additionally, we analyze the eigenvalues of the Riemann tensor using the SO(3, C) representation, which allows us to find, in an invariant way, regions where there may be repulsive effects. Furthermore, we numerically solve the motion equations to show the shadow, the Einstein ring, and the gravitational lensing to establish a possible signature of such repulsive effects. We found that as q is smaller, the Einstein ring decreases, but the shape is the same as the Schwarzschild black hole case. However, for values of q lower or equal than −0.5, repulsive gravitational effects appear in the gravitational lensing close to the compact object, where a strong dependence of the system to the initial conditions seems to take place.

Accretion onto RN-AdS black hole surrounded by quintessence

Accretion is the process by which matter around a compact massive gravitational object or a system flow into its center of mass. In this paper we consider the accretion onto an RN-AdS black hole surrounded by quintessence. We derive the general analytic expressions for the critical points and determine the physical conditions and we also compare our results with the standard Schwarzschild black hole case. At the same time the critical radius, the critical velocity and the mass accretion rate, as well as the gas compression and temperature profile, are found. We find that the accretion rate decreases with the increasing of the charge parameters Q and the quintessence parameter $$\sigma $$ .

Building a linear equation-of-state for trapped gravitons from finite size effects and the Schwarzschild black hole case

In this paper, we continue the investigations present in [S. Viaggiu, Physica A 473 (2017) 412; 488 (2017) 72.] concerning the spectrum of trapped gravitons in a spherical box, and in particular, inside a Schwarzschild black hole (BH). We explore the possibility that, due to finite size effects, the frequency of the radiation made of trapped gravitons can be modified in such a way that a linear equation-of-state [Formula: see text] for the pressure [Formula: see text] and the internal energy [Formula: see text] arises. Firstly, we study the case with [Formula: see text], where only fluids with [Formula: see text] are possible. If corrections [Formula: see text] are added to [Formula: see text], for [Formula: see text], we found no limitation on the allowed value for the areal radius of the trapped sphere [Formula: see text]. Moreover, for [Formula: see text], we have a minimum allowed value for [Formula: see text] of the order of the Planck length [Formula: see text]. Conversely, a fluid with [Formula: see text] can be obtained but with a maximum allowed value for [Formula: see text]. With the added term looking like [Formula: see text] to the BH internal energy [Formula: see text], the well-known logarithmic corrections to the BH entropy naturally emerge for any linear equation-of-state. The results of this paper suggest that finite size effects could modify the structure of graviton’s radiation inside, showing a possible mechanism to transform radiation into dark energy.

The effects of massive graviton on the equilibrium between the black hole and radiation gas in an isolated box

It is well known that the black hole can have temperature and radiate the particles with black body spectrum, i.e. Hawking radiation. Therefore, if the black hole is surrounded by an isolated box, there is a thermal equilibrium between the black hole and radiation gas. A simple case considering the thermal equilibrium between the Schwarzschild black hole and radiation gas in an isolated box has been well investigated previously in detail, i.e. taking the conservation of energy and principle of maximal entropy for the isolated system into account. In this paper, following the above spirit, the effects of massive graviton on the thermal equilibrium will be investigated. For the gravity with massive graviton, we will use the de Rham–Gabadadze–Tolley (dRGT) massive gravity which has been proven to be ghost free. Because the graviton mass depends on two parameters in the dRGT massive gravity, here we just investigate two simple cases related to the two parameters, respectively. Our results show that in the first case the massive graviton can suppress or increase the condensation of black hole in the radiation gas although the T–E diagram is similar as the Schwarzschild black hole case. For the second case, a new T–E diagram has been obtained. Moreover, an interesting and important prediction is that the condensation of black hole just increases from the zero radius of horizon in this case, which is very different from the Schwarzschild black hole case.

Gyroscope precession along unbound equatorial plane orbits around a Kerr black hole

The precession of a test gyroscope along unbound equatorial plane geodesic orbits around a Kerr black hole is analyzed with respect to a static reference frame whose axes point towards the ``fixed stars.'' The accumulated precession angle after a complete scattering process is evaluated and compared with the corresponding change in the orbital angle. Limiting results for the nonrotating Schwarzschild black hole case are also discussed.

Asymptotic quasi-normal frequencies, horizon area spectra and multi-horizon spacetimes

There exists a long term debate about a possible link of the asymptotic quasinormal (QNM) modes to the black hole thermodynamics. The first conjecture providing a link between the classical asymptotic black hole oscillation frequencies and black hole thermodynamics was formulated more than a decade ago by Hod. The conjecture was later modified by Maggiore. We analyse the behavior of the asymptotic frequencies of the spherically symmetric multi-horizon spacetimes (in particular Reissner-Nordström, Schwarzschild-deSitter, Reissner-Nordström-deSitter spacetime) and provide some suggestions for how to interpret the results following the spirit of the modified Hod's conjecture. The interpretation suggested is in some sense analogical to the Schwarzschild black hole case, but has some new specific features. This paper1 refers to work done over a longer period of time contained in papers [1, 2, 3, 4] and also to some extent in [5].

Strong field limit analysis of gravitational lensing in Kerr-Taub-NUT spacetime

In this paper, we study numerically the quasi-equatorial lensing by the stationary, axially-symmetric black hole in Kerr-Taub-NUT spacetime in the strong field limit. The deflection angle of light ray and other strong deflection limit coefficients are obtained numerically and they are found to be closely dependent on the NUT charge n and spin a. We also compute the magnification and the positions of the relativistic images. The caustics are studied and the results show that these caustics drift away from the optical axis, which is quite different from the Schwarzschild black hole case. Moreover, the intersections of the critical curves on the equatorial plane are obtained and it is shown that they increase with the NUT charge. These results show that there is a significant effect of the NUT charge on the strong gravitational lensing.

Fermion fields in the soliton background of Kaluza-Klein theories.

Field equations for neutrinos and electrons in the background of soliton solutions of the five-dimensional Kaluza-Klein theory are formulated and illustrated in the spherically symmetric soliton cases. Neutrino equations are decoupled into ordinary differential equations which agree with those obtained by the null-tetrad formalism in the Schwarzschild black-hole case.

Gravitational radiation induced by a particle falling along the Z-axis into a Kerr black hole

We have computed the spectrum and the energy of gravitational radiation induced by a test particle of mass μ falling along the z-axis into a Kerr black hole of mass M(⪢ μ) and angular momentum Ma( a < M). It is found that the total energy radiated is 0.0170 0.0170 μc 2 μM when α = 0.99 M, which is 1.65 times larger than that when α = 0, i.e., the Schwarzschild black hole case.