Temperature Profile of Black Hole Accretion Disc with Magnetic Coupling

Two new mapping relations between the angular coordinate on the black hole (BH) horizon and radialcoordinate on the disc are given according to the requirement of general relativity and Maxwell‘s equations, and theeffects of magnetic coupling (MC) on temperature of accretion disc are investigated by comparing with pure accretion.It is shown that the MC effects on the temperature profile are related intimately to the BH spin, and the influenceon the peak value of disc temperature based on the modified mapping relations is not as great as that based on thelinear mapping.The peak value and the corresponding radius of peak value ring of disc temperature do not increasemonotonically as the increasing spin of BH, each containing a maximum for the fast-spinning BH. The value ranges ofthe bolometric luminosity and color temperature of the disc are both extended by the MC effects.     

Dark Energy Accretion onto a Black Hole in an Expanding Universe

By using the solution describing a black hole embedded in the FLRW universe, we obtain the evolving equation of the black hole mass expressed in terms of the cosmological parameters. The evolving equation indicates that in the phantom dark energy universe the black hole mass becomes zero before the Big Rip is reached.     

Nucleosynthesis in Advection-Dominated Accretion Flow onto a Black Hole

Nucleosynthesis in advection-dominated accretion flow(ADAF) onto a black hole is proposed to be an important role in chemical evolution around compact stars. We investigate the nucleosynthesis in ADAF relevant for a black hole of low mass,different from that of the self-similar solution. in particular,the presence of supersolar metal mass fractions of some isotopes seems to be associated with the known black hole nucleosynthesis in ADAF,which offers further evidence of diversity of the chemical enrichment.     

Two Kinds of Magnetic Connection in Black-Hole Accretion Disc

We discuss two kinds of magnetic connection （MC） in the black hole （BH） accretion disc： the magnetic connection between the BH and the disc （MCHD） and that between the plunging region and the disc （MCPD）. The magnetic field configuration is produced by an electric current flowing at the inner edge of the disc. It turns out that the transfer direction of energy and angular momentum depends on the BH spin and a parameter λ for adjusting the angular velocities of the plunging matter, which corresponds to at most five regions in the disc. The effect of MCPD results in a much steeper emissivity than a standard accretion disc in the inner disc, however it fails to reach the observation range 4.3-5.5 in several objects, such as Seyfert 1 galaxy MCG-6-30-15, microquasars XTE J1650-500 and GX 399-4.     

Standing Rankine-Hugoniot Shocks in Black Hole Accretion Discs

We study the problem of standing shocks in viscous disc-like accretion flows around black holes. For the first time we parametrize such a flow with two physical constants, namely the specific angular momentum accreted by the black hole j and the energy quantity K. By providing the global dependence of shock formation in the j- K parameter space, we show that a significant parameter region can ensure solutions with Rankine-Hugoniot shocks; and that the possibilities of shock formation are the largest for inviscid flows, decreasing with increasing viscosity, and ceasing to exist for a strong enough viscosity. Our results support the view that the standing shock is an essential ingredient in black hole accretion discs and is a general phenomenon in astrophysics, and that there should be a continuous change from the properties of inviscid flows to those of viscous ones.     

Accretion of Phantom Energy by Bardeen Black Hole

In this paper we deal with the accretion of phantom energy onto static spherically symmetric Bardeen black hole. It is shown that the mass of black hole reduces with the accretion of phantom energy. We compute accretion rate onto Bardeen black hole at critical point. Furthermore, we obtain the conditions at critical point, under which accretion is possible and also discuss certain relevant cases. Finally, we discuss the validity of generalized second law of thermodynamics at the event horizon of Bardeen black hole.     

Phantom Accretion onto the Schwarzschild AdS Black Hole with Topological Defect

In this paper, we have studied phantom energy accretion of prefect fluid onto the Schwarzschild AdS black hole with topological defect. We have obtained critical point during the accretion of fluid on the black hole where the speed of flow is equal speed of sound (Sharif and Abbas in Phantom accretion onto the Schwarzschild de-Sitter black hole, 2011, [gr-qc]). The critical velocities have been computed so that the speed of fluid into the black hole is less than speed of sound. Finally, we have found that the critical point is near the black hole horizon.     

Stability of Circular Orbits around a Tidal Charged Black Hole

We study the effects of the tidal charge on the equatorial circular motion of neutral test particles near a tidal charged black hole. This analysis investigates stable as well as unstable circular orbits in all possible configurations of nonextremal and extremal cases. It is found that a negative tidal charge will increase the energy and angular momentum of a neutral test particle moving around a black hole. We obtain a continuous region of stability for both extremal and nonextremal cases. We conclude that the region of stability as well as radius of last stable circular orbit shows increasing behavior for Q < 0.     

Quasinormal Modes of Electromagnetic Perturbation around a Stringy Black Hole

We investigate the electromagnetic perturbation around a stringy black hole. A second-order differential equation is obtained for the perturbation. The variation of the effective potential with r is presented. The complex frequencies of the quasinormal modes of electromagnetic perturbation around a stringy black hole are computed by the third Wentzel-Kramers-Brillouin （WKB） approximation. The results show that the parameters resulted from the compactification of higher dimensions can influence the quasinormal complex frequencies, and the Maxwell field around a stringy black hole damps more slowly than that around a Schwarzschild black hole.     

Neutral Particle Motion around a Schwarzschild Black Hole in Modified Gravity

We investigate circular motion of neutral test particles on equatorial plane near a black hole in scalar-tensor-vector gravity. We consider three cases (i) α < G/G_N (ii) α = G/G_N and (iii) α > G/G_N to find the regions where motion can exist. The corresponding effective potential, energy, angular momentum and center of mass energy are evaluated. Further, we define four different cases for α > G/G_N and identify stable and unstable regions of circular orbits. It is found that circular orbits having zero angular momentum exist at r = αGNM due to repulsive gravity effects. We conclude that the structure of stable regions for α < G/G_N as well as α = G/G_N case is completely different from that of α > G/G_N.     

Magnetoelastic Instability of a Long Graphene Nano-Ribbon Carrying Electric Current

This paper aims at investigating the resonance frequencies and stability of a long Graphene Nano-Ribbon (GNR) carrying electric current. The governing equation of motion is obtained based on the Euler-Bernoulli beam model along with Hamilton's principle. The transverse force distribution on the GNR due to the interaction of the electric current with its own magnetic field is determined by the Biot-Savart and Lorentz force laws. Using Galerkin's method, the governing equation is solved and the effect of current strength and dimensions of the GNR on the stability and resonance frequencies are investigated.     

Quasi-Normal Modes of Gravitational Perturbation around a Reissner-Nordstroem Black Hole Surrounded by Quintessence

We investigate quasi-normal （QN） modes of gravitational perturbation around a Reissner-Nordstroem black hole surrounded by quintessence. The third-order Wentzel-Kramers-Brillouin approximation is used to evaluate QN frequencies. The behavior of the gravitational perturbation is plotted for some frequencies. Due to the presence of quintessence, QN modes of the Reissner-Nordstroem black hole damp at a slower rate.     

Transverse Wave Propagation in Relativistic Two-Fluid Plasmas around Schwarzschild-de Sitter Black Hole

We investigate transverse electromagnetic waves propagating in a plasma influenced by the gravitational field of the Schwarzschild-de Sitter black hole. Applying 3+1 spacetime split we derive the relativistic two-fluid equations to take account of gravitational effects due to the event horizon and describe the set of simultaneous linear equations for the perturbations. We use a local approximation to investigate the one-dimensional radial propagation of Alfvén and high frequency electromagnetic waves. We derive the dispersion relation for these waves and solve it for the wave number k numerically.     

Entropy of an Arbitrarily Accelerating Black Hole

The entropy of an arbitrarily accelerating black hole is studied. As the metric is neither axisymmetric nor stationary, its entropy is difficult to calculate. We overcome the difficulty via introduction of a new coordinate system in which ₀₀ is zero at the event horizon's surface r = r _h , and calculate the entropy locally via the improved brick-wall model, that is, the thin film model with the locally thermal equilibrium satisfied. The results confirm that the entropy is proportional to its area both in the stationary space-time and non-stationary one.     

Chaotic Motion of a Charged Particle around a Weakly Magnetized Schwarzschild Black Hole Containing Cosmic String

We discuss the conditions where a charged particle that was originally revolving around a weakly magnetized black hole containing cosmic string in the innermost stable circular orbit will escape to infinity after it is kicked by another particle or photon. We find that the motion of the kicked particle is chaotic. The critical escape energy and velocity of the kicked charged particle with different initial radial velocities are obtained.     

Quantum Corrections for a Black Hole in an Asymptotically Safe Gravity with Higher Derivatives

By using the quantum tunneling approach over semiclassical approximations, we study the quantum corrections to the Hawking temperature, entropy and Bekenstein-Hawking entropy-area relation for a black hole in an asymptotically safe gravity with higher derivatives. The leading and non leading corrections to the area law are obtained.     

Entropy of a Black Hole with Distinct Surface Gravities

In gravitational thermodynamics, the entropy of a black hole with distinct surface gravities can be evaluated in a microcanonical ensemble. At the WKB level, the entropy becomes the negative of the Euclidean action of the constrained instanton, which is the seed for the black hole creation in the no-boundary universe. Using the Gauss-Bonnet theorem, we prove the quite universal formula in Euclidean quantum gravity that the entropy of a nonrotating black hole is one quarter the sum of the products of the Euler characteristics and the areas of the horizons. For Lovelock gravity, the entropy and quantum creation of a black hole are also studied.     

Area Spectrum of a Kerr-Newman Black Hole Via an Adiabatic Invariant

By virtue of a semiclassical adiabatic invariant in this paper, we quantize the horizon area of a Kerr-Newman black hole by making use of the period of the gravity system. We exploit exclusively the basic properties of the adiabatic invariant. It is found that the result produced by our method is consistent with the one obtained by calculating the adiabatic invariant step by step.     

Entangled Particles Tunneling From a Schwarzschild Black Hole immersed in an Electromagnetic Universe with GUP

Quantum gravity has exciting peculiarities on the Planck scale.The effect of generalized uncertainty principle (GUP) to the entangled scalar/fermion particles’ tunneling from a Schwarzschild black hole immersed in an electromagnetic Universe is investigated by the help of semi-classical tunneling method. The quantum corrected Hawking temperature of this black hole with an external parameter “a” modifies the Hawking temperature for the entangled particles.