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1.
Now there are two basic observational techniques to investigate a gravitational potential at the Galactic Center, namely, (a) monitoring the orbits of bright stars near the Galactic Center to reconstruct a gravitational potential; (b) measuring the size and shape of shadows around black hole giving an alternative possibility to evaluate black hole parameters in mm-band with VLBI-technique. At the moment, one can use a small relativistic correction approach for stellar orbit analysis (however, in the future the approximation will not be precise enough due to enormous progress of observational facilities) while for smallest structure analysis in VLBI observations one really needs a strong gravitational field approximation. We discuss results of observations, their conventional interpretations, tensions between observations and models and possible hints for a new physics from the observational data and tensions between observations and interpretations. We discuss an opportunity to use a Schwarzschild metric for data interpretation or we have to use more exotic models such as Reissner–Nordstrom or Schwarzschild–de-Sitter metrics for better fits.  相似文献   

2.
The radial motion along null geodesics in static charged black hole space–times, in particular, the Reissner–Nordström and stringy charged black holes, are studied. We analyzed the properties of the effective potential. The circular photon orbits in these space–times are investigated. We found that the radius of circular photon orbits in both charged black holes are different and differ from that given in Schwarzschild space–time. We studied the physical effects of the gravitational field between two test particles in stringy charged black hole and compared the results with that given in Schwarzschild and Reissner–Nordström black holes.  相似文献   

3.
The Hawking radiation is considered as a quantum tunneling process, which can be studied in the framework of the Hamilton–Jacobi method. In this study, we present the wave equation for a mass generating massive and charged scalar particle (boson). In sequel, we analyse the quantum tunneling of these bosons from a generic 4-dimensional spherically symmetric black hole. We apply the Hamilton–Jacobi formalism to derive the radial integral solution for the classically forbidden action which leads to the tunneling probability. To support our arguments, we take the dyonic Reissner–Nordström black hole as a test background. Comparing the tunneling probability obtained with the Boltzmann formula, we succeed in reading the standard Hawking temperature of the dyonic Reissner–Nordström black hole.  相似文献   

4.
Using the Darmois–Israel formalism the dynamical analysis of Reissner Nordstrom de-Sitter thin shell wormholes, at the wormhole throat, are determined by considering linearized radial perturbations around static solutions.The region of stability in the presence of a large value of charge is significantly increased. Also, the region of stability in the presence of a positive large value of cosmological constant is significantly increased.  相似文献   

5.
We calculate the fields surrounding and the power radiated by a slowly rotating neutron star with a frozen-in magnetic dipole field, tilted with respect to the rotation axis, including the effects of spacetime curvature. The general relativistic effects suppress the radiated power relative to flat space by factors up to 1/7 for magnetic dipole radiation and 1/50 for the associated electric quadrupole radiation. This suppression exceeds that which might be expected from a surface red shift alone.Numerical results are found using power series which describe the behavior of electromagnetic fields exterior to a black hole or slowly rotating neutron star. These new solutions, appropriate near the stellar surface, converge for all radii exterior to the neutron star (or black hole) making analytic continuation of the power series unnecessary as well as allowing matching to a linear combination of asymptotic expansions, appropriate for large radius. Typical numerical values for these functions are presented as well as techniques for accelerating the convergence of their respective power series which make them attractive alternatives to numerical integration.Supported in part by NSF Grant PHY 77 28356.  相似文献   

6.
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7.
In this article the charged analogues of recently derived Buchdahl’s type fluid spheres have been obtained by considering a particular form of electric field intensity. In this process, Einstein–Maxwell field equations yield eight different classes of solutions, joining smoothly with the exterior Reissner–Nordstrom metric at the pressure free intersurface. Out of the eight solutions only seven could be utilized to represent superdense star models with ultrahigh surface density of the order 2×1014 gm cm−3. The maximum masses of the star models were found to be 8.223931MΘ and 8.460857MΘ subject to strong and weak energy conditions, respectively, which are much higher than the maximum masses 3.82MΘ and 4.57MΘ allowed in the neutral cases. The velocity of sound seen to be less than that of light throughout the star models.  相似文献   

8.
In this paper, the orbital dynamics of the gravitational field in Bardeen space-time are investigated. The equations of the particle’s orbital motion are given by solving the Lagrangian equation, and the stability and types of orbits are studied by means of analysing the effective potential of particles. Also, with the help of phase-plane method, the closed and non-closed orbits of test particle are analysed. We find that the stability and types of orbits in the Bardeen space-time are determined not only by the particles’ energy but also by the angular momentum. And for q=0.5M and b<3.3731M, absorbed by the black hole is the only fate of the test particle. We also find that the position of the innermost stable circular orbit of Bardeen black hole occurs at r min =5.5722M.  相似文献   

9.
The growth of supermassive black holes by merging and accretion in hierarchical models of galaxy formation is studied by means of Monte Carlo simulations. A tight linear relation between masses of black holes and masses of bulges arises if the mass accreted by supermassive black holes scales linearly with the mass-forming stars and if the redshift evolution of mass accretion tracks closely that of star formation. Differences in redshift evolution between black hole accretion and star formation introduce a considerable scatter in this relation. A non-linear relation between black hole accretion and star formation results in a non-linear relation between masses of remnant black holes and masses of bulges. The relation of black hole mass to bulge luminosity observed in nearby galaxies and its scatter are reproduced reasonably well by models in which black hole accretion and star formation are linearly related but do not track each other in redshift. This suggests that a common mechanism determines the efficiency for black hole accretion and the efficiency for star formation, especially for bright bulges.  相似文献   

10.
It has long been known that galaxy interactions are associated with enhanced star formation. In a companion paper, we explored this connection by applying a variety of statistics to Sloan Digital Sky Survey (SDSS) data. In particular, we showed that specific star formation rates of galaxies are higher if they have close neighbours. Here, we apply exactly the same techniques to active galactic nuclei (AGN) in the survey, showing that close neighbours are not associated with any similar enhancement of nuclear activity. Star formation is enhanced in AGN with close neighbours in exactly the same way as in inactive galaxies, but the accretion rate on to the black hole, as estimated from the extinction-corrected [O  iii ] luminosity, is not influenced by the presence or absence of companions. Previous work has shown that galaxies with more strongly accreting black holes contain more young stars in their inner regions. This leads us to conclude that star formation induced by a close companion and star formation associated with black hole accretion are distinct events. These events may be part of the same physical process, for example a merger, provided they are separated in time. In this case, accretion on to the black hole and its associated star formation would occur only after the two interacting galaxies have merged. The major caveat in this work is our assumption that the extinction-corrected [O  iii ] luminosity is a robust indicator of the bolometric luminosity of the central black hole. It is thus important to check our results using indicators of AGN activity at other wavelengths.  相似文献   

11.
In the framework of Darmois-Israel formalism, the general equations describing the motion of thin shell wormhole with a general form of equation of state of a polytropic gas are derived. The mechanical stability analysis of thin shell wormhole with charge in Reissner–Nordstrom (RN) to linearized spherically symmetric perturbation about static equilibrium solution is carried out.  相似文献   

12.
The thermodynamics of the Reissner–Nordström black hole at the charge-to-mass ratio of \(\sqrt{3}/2\) is studied. We show that there exists infinite discontinuity not only in the heat capacity but also in the electromagnetic potential and hence in the Gibbs free energy. Despite the existence of an infinite discontinuity in the heat capacity, it is shown that there exists no phase transition in the Reissner–Nordström black hole. The discontinuity may be merely an artefact of the change in the slope of the |Q| vs. M curve when the charge-to-mass ratio crosses \(\sqrt{3}/2\). This may signify that the horizon temperature is not a well-behaved thermodynamic parameter in the black hole thermodynamics.  相似文献   

13.
We obtain a new parametric class of exact solutions of Einstein–Maxwell field equations which are well behaved. We present a charged super-dense star model after prescribing particular forms of the metric potential and electric intensity. The metric describing the super dense stars joins smoothly with the Reissner–Nordstrom metric at the pressure free boundary. The electric density assumed is where n may take the values 0,1,2,3,4 and so on and K is a positive constant. For n=0,1 we rediscover the solutions by Gupta and Maurya (Astrophys. Space Sci. 334(1):155, 2011) and Fuloria et al. (J. Math. 2:1156, 2011) respectively. The solution for n=2 have been discussed extensively keeping in view of well behaved nature of the charged solution of Einstein–Maxwell field equations. The solution for n=3 and n=4 can be also studied likewise. In absence of the charge we are left behind with the regular and well behaved fifth model of Durgapal (J. Phys. A 15:2637, 1982). The outmarch of pressure, density, pressure-density ratio and the velocity of sound is monotonically decreasing, however, the electric intensity is monotonically increasing in nature. For this class of solutions the mass of a star is maximized with all degree of suitability, compatible with Neutron stars and Pulsars.  相似文献   

14.
Hawking radiation can be viewed as a process of particle quantum tunneling near a black hole horizon. When a particle with angular momentum tunnels across the event horizon of a Reissner–Nordstrom black hole, the black hole will change into a Kerr–Newman one. In previous papers, axisymmetric black hole has been studied only when a keeps constant. Changing from Reissner–Nordstrom to Kerr–Newman should be a simple case when a varies. After this, more general radiation including changed a in Kerr or Kerr–Newman spacetimes can be studied in the future. The emission rate of the massless particles with angular momentum is calculated, and the result is consistent with an underlying unitary theory.   相似文献   

15.
GRB 170817A was confirmed to be associated with GW170817, which was produced by a neutron star - neutron star merger. It indicates that at least some short gamma-ray bursts come from binary neutron star mergers. Theoretically, it is widely accepted that short gamma-ray bursts can be produced by two distinctly different mechanisms, binary neutron star mergers and neutron star - black hole mergers. These two kinds of bursts should be different observationally due to their different trigger mechanisms. Motivated by this idea, we collect a universal data set constituted of 51 short gamma-ray bursts observed by Swift/BAT, among which 14 events have extended emission component. We study the observational features of these 51 events statistically. It is found that our samples consist of two distinct groups. They clearly show a bimodal distribution when their peak photon fluxes at 15–150 keV band are plotted against the corresponding fluences. Most interestingly, all the 14 short bursts with extended emission lie in a particular region of this plot. When the fluences are plotted against the burst durations, short bursts with extended emission again tend to concentrate in the long duration segment. These features strongly indicate that short gamma-ray bursts really may come from two distinct types of progenitors. We argue that those short gamma-ray bursts with extended emission come from the coalescence of neutron stars, while the short gamma-ray bursts without extended emission come from neutron star - black hole mergers.  相似文献   

16.
Data from the Fermi Gamma-ray Burst Monitor satellite observatory suggested that the recently discovered gravitational wave source, a pair of two coalescing black holes, was related to a gamma-ray burst. The observed high-energy electromagnetic radiation (above 50 keV) originated from a weak transient source and lasted for about 1 s. Its localization is consistent with the direction to GW150914. We speculate about the possible scenario for the formation of a gamma-ray burst accompanied by the gravitational-wave signal. Our model invokes a tight binary system consisting of a massive star and a black hole which leads to the triggering of a collapse of the star’s nucleus, the formation of a second black hole, and finally to the binary black hole merger. For the most-likely configuration of the binary spin vectors with respect to the orbital angular momentum in the GW150914 event, the recoil speed (kick velocity) acquired by the final black hole through gravitational wave emission is of the order of a few hundred km/s and this might be sufficient to get it closer to the envelope of surrounding material and capture a small fraction of matter from the remnant of the host star. The gamma-ray burst is produced by the accretion of this remnant matter onto the final black hole. The moderate spin of the final black hole suggests that the gamma-ray burst jet is powered by weak neutrino emission rather than the Blandford–Znajek mechanism, and hence explains the low power available for the observed GRB signal.  相似文献   

17.
Our study illuminates the effects of gravitational collapse by considering heat flux anisotropic matter sources within the framework of the f(R) theory of gravity. We assume the non-static spherically symmetric configuration to narrate the nature of the interior spacetime and match it with the Vaidya exterior geometry. Further, we employ the well-known Karmarkar condition, as it reduces the solution-generating method of field equations to a single metric potential. To ensure the viability of our collapsing system, a comprehensive graphical analysis is presented in the context of the Logarithmic-corrected R2 gravity model. Our investigation argues that there are no traces of trapped surfaces in the collapsing procedure. Thus, naked singularity and black hole are not the final fate of the gravitational collapse.  相似文献   

18.
In this paper, perturbations of an accretion disk by a star orbiting around a black hole are studied. We report on a numerical experiment, which has been carried out by using a parallel-machine code originally developed by Dönmez (2004). An initially steady state accretion disk near a non-rotating (Schwarzschild) black hole interacts with a “star”, modeled as an initially circular region of increased density. Part of the disk is affected by the interaction. In some cases, a gap develops and shock wave propagates through the disk. We follow the evolution for order of one dynamical period and we show how the non-axisymetric density perturbation further evolves and moves downwards where the material of the disk and the star become eventually accreted onto the central body. When the star perturbs the steady state accretion disk, the disk around the black hole is destroyed by the effect of perturbation. The perturbed accretion disk creates a shock wave during the evolution and it loses angular momentum when the gas hits on the shock waves. Colliding gas with the shock wave is the one of the basic mechanism of emitting the X-rays in the accretion disk. The series of supernovae occurring in the inner disk could entirely destroy the disk in that region which leaves a more massive black hole behind, at the center of galaxies.  相似文献   

19.
This paper is devoted to study the effects of electromagnetic on the collapse and expansion of anisotropic gravitating source. For this purpose, we have evaluated the generating solutions of Einstein–Maxwell field equations with spherically symmetric anisotropic gravitating source. We found that a single function generates the various anisotropic solutions. In this case every generating function involves an arbitrary function of time which can be chosen to fit several astrophysical time profiles. Two physical phenomenon occur, one is gravitational collapse and other is the cosmological expanding solution. In both cases electromagnetic field effects the anisotropy of the model. For collapse the anisotropy is increased while for expansion it deceases from maximum value to finite positive value. In case of collapse there exits two horizons like in case of Reissner–Nordström metric.  相似文献   

20.
We present a number of calculations involving the production and propagation of electromagnetic waves in the Schwarzschild metric. They are based on algorithms developed from the power series solutions of the Schwarzschild radial equation (Regge-Wheeler equation) of Arenstorf, Cohen and Kegeles. These include the scattering of electromagnetic plane waves from a Schwarzschild black hole where we find that previous approximate and numerical work is correct and extend those results to higher frequencies and multipolarities. Exact results for the absorption cross-section are presented. We calculate the power radiated from a radially vibrating neutron star and find that the radiation can be hyperemissive. For example, we find for a surface radius of 1.8 Schwarzschild radii the power radiated is enhanced by as much as factor of 3.7, 4.1, 5.1, for dipole, quadrupole and octupole radiation respectively, making electromagnetic radiation a more effective damping mechanism than in flat space. The Schwarzschild radial functions are extensively treated in the appendices and numerical results are presented for various frequencies and radii. A simple asymptotic expansion for one of the connection constants, appropriate for high frequency, is also given.Supported in part by NSF Grant PHY 77-28356.  相似文献   

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