Constraints on Slim Accretion Discs

We show that when the gravitational force in the vertical direction is correctly calculated, the well-known S- shaped sequence of thermal equilibrium solutions can be constructed only for small radii of black hole accretion flows, such that slim accretion discs can possibly exist only in the inner regions of these flows.     

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.     

Slim Discs with Varying Accretion Rates

It was revealed in our previous studies that there exists a maximal possible accretion rate for slim discs with constant accretion rates because the correctly calculated vertical gravitational force can only gather some limited amount of accreted matter. Here we show that when the accretion rate is not constant and instead decreases with decreasing radius because of outflows, such that the amount of accreted matter is adjusted to be within the allowed limit, global slim disc solutions can be constructed even for the case that accretion rates at large radii apparently exceed the maximal possible value. This result further demonstrates that outflows seem to be unavoidable for accretion flows with large accretion rates at large radii.     

A Toy Model for Magnetic Field Configurations in Black Hole Accretion Discs

We discuss the feature of the magnetic field configuration arising from double counter oriented electric currentrings in the accretion disc around a Kerr black hole （BH）. We discuss the relevant physical quantities corresponding to this configuration： （1） the power and torque transferred by the large-scale magnetic field, （2） the angular momentum and energy fluxes transferred from the BIt to the inner disc, （3） the radiation flux from the disc. In addition, we discuss the possibility that the closed magnetic field anchored at the disc probably evolves to the open magnetic field, which is helpful to produce the jet from the disc.     

Non-Thermal Photon Emission from Shell-Type Supernova Remnants

We study the non-thermal photon emission from shell-type supernova remnants （SNRs） in the frame of a two-zone model. In this model, the sites of acceleration, escape and subsequent radiation of particles （both electron and proton） are divided into acceleration and escape zones, respectively. The particle distributions consist of two components, one is produced inside the acceleration zone, the other in the escape zone. We apply this model to two young and one old shell-type SNRs and show that the observed multi-waveband photon spectra for the three SNRs can be explained well in this model and high-energy γ-rays from these SNRs may have hadronic origins.     

Leptonic Origin of TeV Gamma-Ray Emission from Crab Nebula

We study the nonthermal emission of the Crab nebula in the bands from radio to TeV γ-ray on a simplified timedependent injection model. In this model, relativistic electrons in the Crab nebula consists of two components and their injected spectrum is a broken power law with different indices and a break energy. The relativistic electrons emit nonthermal photons through synchrotron and inverse Compton scattering off soft photon fields inside the nebula. The resulting spectrum calculated with the model is well consistent with the observed data ranging from radio to very high energy γ-rays for the Crab nebula, where the emission from radio to medium γ-rays is from electron＇s synchrotron emission, whereas the emission above ～ 100 MeV primarily comes from the inverse Compton scattering of the relativistic electrons on synchrotron photons.     

Quasinormal modes in the background of charged Kaluza–Klein black hole with squashed horizons

We study the scalar perturbation in the background of the charged Kaluza–Klein black holes with squashed horizons. We find that the position of infinite discontinuities of the heat capacities can be reflected in quasinormal spectrum. This shows the possible non-trivial relation between the thermodynamical and dynamical properties of black holes.     

Quasinormal modes of black holes absorbing dark energy

We study perturbations of black holes absorbing dark energy. Due to the accretion of dark energy, the black hole mass changes. We observe distinct perturbation behaviors for absorption of different forms of dark energy onto the black holes. This provides the possibility of extracting information whether dark energy lies above or below the cosmological constant boundary w=−1$w=-1$. In particular, we find in the late time tail analysis that, differently from the other dark energy models, the accretion of phantom energy exhibits a growing mode in the perturbation tail. The instability behavior found in this work is consistent with the Big Rip scenario, in which all of the bound objects are torn apart with the presence of the phantom dark energy.     

Vacuum Outer-Gap Structure in Pulsar Outer Magnetospheres

We study the vacuum outer-gap structure in the outer magnetosphere of rotation-powered pulsars by considering the limit of trans-field height through a pair production process. In this case, the trans-field height is limited by the photon-photon pair production process and the outer boundary of the outer gap can be extended outside the light cylinder. By solving self-consistently the Poisson equation for electrical potential and the Boltzmann equations of electrons/positrons and γ-rays in a vacuum outer gap for the parameters of Vela pulsar, we obtain an approximate geometry of the outer gap, i.e. the trans-field height is limited by the pair-production process and increases with the radial distance to the star and the width of the outer gap starts at the inner boundary （near the null charge surface） and ends at the outer boundary which locates inside or outside the light cylinder depending on the inclination angle.     

Hawking Radiation from Topological Kerr Anti-de-Sitter Black Hole with One Rotational Parameter via Covariant Anomalies

Using anomalous viewpoint, we study the Hawking radiation from a kind of topological Kerr Anti-de-Sitter （Kerr-AdS） black hole with one rotational parameter. We employ the covariant gauge and gravitational anomalies. The result supports the Robinson-Wilczek opinion and shows that the Hawking temperature can be correctly determined by cancelling covariant gauge and gravitational anomalies at the horizon.     

A New Method to Study Hawking Radiation of Charged Particle from Stationary Axisymmetric Sen Black Hole

Taking the self-gravitation interaction and energy conservation,charge conservation and angular momentum conservation into accpunt, we discuss the tunnelling characteristics of the charged particle from Sen black hole by the Hamilton-Jacobi method. The result shows that the tunnelling probability is related to the change of Bekenstein-Hawking entropy, and the actual radiation spectrum deviates from the pure thermal one, which is consistent with the result of Parikh and Wilczek and gives a new method to correct the Hawking pure thermal spectrum of Sen black hole.     

Fermion Tunnelling of a New Form Finslerian Black Hole

We improve the fermion tunnelling theory proposed by Kerner and Mann, and research into the fermion tunnelling radiation from a Finslerian black hole. The Finsler black hole put forward by Rutz is a solution of Einstein＇s vacuum field equations in Finsler theory. We study the radiation from the black hole with a semi-classical method, and the result proves that the tunnelling rate depends on the tangent vector.     

Generalized uncertainty principle and black hole entropy

Recently, there has been much attention devoted to resolving the quantum corrections to the Bekenstein–Hawking black hole entropy. In particular, many researchers have expressed a vested interest in the coefficient of the logarithmic term of the black hole entropy correction term. In this Letter, we calculate the correction value of the black hole entropy by utilizing the generalized uncertainty principle and obtain the correction terms of entropy, temperature and energy caused by the generalized uncertainty principle. We calculate Cardy–Verlinde formula after considering the correction. In our calculation, we only think that the Bekenstein–Hawking area theorem is still valid after considering the generalized uncertainty principle and do not introduce any assumption. In the whole process, the physics idea is clear and calculation is simple. It offers a new way for studying the corrections caused by the generalized uncertainty principle to the black hole thermodynamic quantity of the complicated spacetime.     

Charged Particle Tunnels from the Slowly Varying Reissner-Nordstroem Black Hole

Extending Parikh and Wilczek＇s work to the non-stationary black hole, we discuss the Hawking radiation of the slowly varying Reissner-NordstrSm black hole by considering the unfixed background spacetime and the selfgravitation interaction. The result shows that the tunnelling rate is related to both the variation of BekensteinHawking entropy and the radiation spectrum deviating from the purely thermal one. This is in agreement with Parikh and Wilczek＇s result. Then a new method to study Hawking radiation of the non-stationary black holes is presented.     

Dirac Particles＇ Hawking Radiation from a Schwarzschild Black Hole

Considering energy conservation and the backreaction of particles to spacetime, we investigate the massless/massive Dirac particles＇ Hawking radiation from a Schwarzschild black hole, The exact expression of the emission rate near the horizon is obtained and the result indicates that Hawking radiation spectrum is not purely thermal. The result obtained is consistent with the results obtained before. It satisfies the underlying unitary theory and offers a possible mechanism to explain the information loss paradox. Whereas the improved Damour-Rufflni method is more concise and understandable,     

Geodesics of Spherical Dilaton Spacetimes

The properties of spherical dilaton black hole spacetimes are investigated through a study of their geodesics. The closed and non-closed orbits of test particles are analysed using the effective potential and phase-plane method. The stability and types of orbits are determined in terms of the energy and angular momentum of the test particles. The conditions of the existence of circular orbits for a spherical dilaton spacetime with an arbitrary dilaton coupling constant α are obtained. The properties of the orbits and in particular the position of the innermost stable circular orbit are compared to those of the Reissner-Nordstrom spacetime. The circumferential radius of innermost stable circular orbit and the corresponding angular momentum of the test particles increase for α≠ 0.     

Viscous Cosmology and Thermodynamics of Apparent Horizon

It is shown that the differential form of Friedmann equations of Friedman--Robertson--Walker (FRW) universe can be recast as a similar form of the first law T_hdS_h = dE + WdV of thermodynamics at the apparent horizon of FRW universe filled with the viscous fluid. It is also shown that by employing the general expression of temperature associated with the apparent horizon of an FRW universe and assumed that the temperature T_m of the energy inside the apparent horizon is proportional to the horizon temperature T_m= bT_h, we are able to show that the generalized second law of thermodynamics holds in the Einstein gravity provided T_h-T_m/r^~_A ≤(ρ+P^~).     

Gauss-Bonnet and Lovelock Gravities and the Generalized Second Law of Thermodynamics

It has been shown [Chin. Phys. Lett.25 （2008） 4199] that the generalized second law of thermodynamics holds in Einstein gravity. Here we extend this procedure for Gauss-Bonnet and Lovelock gravities. It is shown that by employing the general expression for temperature Th =｜κ｜/2π= 1/2πτA （1-τA/2HτA） associated with the apparent horizon of a Friedman Robertson-Walker （FRW） universe and assuming Tm = bTh, we are able to construct conditions for which the generalized second law holds in Gauss Bonnet and Lovelock gravities, where Tm and Th are the temperatures of the source and the horizon respectively.     

Thermodynamic Interpretation of Field Equations at Horizon of BTZ Black Hole

A spacetime horizon comprising with a black hole singularity acts like a boundary of a thermal system associated with the notions of temperature and entropy. In the case of static metric of Banados-Teitelboim-Zanelli （BTZ） black hole, the field equations near the horizon boundary can be expressed as a thermal identity dE = TdS＋ Pr dA, where E = M is the mass of BTZ black hole, dA is the change in the area of the black hole horizon when the horizon is displaced infinitesimally small, Pr is the radial pressure provided by the source of Einstein equations, S = 41πa is the entropy and T =κ/2π is the Hawking temperature associated with the horizon. This approach is studied further to generalize it for non-static BTZ black hole, showing that it is also possible to interpret the field equation near horizon as a thermodynamic identity dE = TdS ＋ PrdA ＋Ω＋dJ, where Ω＋ is the angular velocity and J is the angular momentum of BTZ black hole. These results indicate that the field equations for BTZ black hole possess intrinsic thermodynamic properties near the horizon.