共查询到20条相似文献，搜索用时 15 毫秒
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As is well known, black hole entropy is proportional to the area of the horizon suggesting a holographic principle wherein all degrees of freedom contributing to the entropy reside on the surface. In this note, we point out that large scale dark energy (such as a cosmological constant) constraining cosmic structures can imply a similar situation for the entropy of a hierarchy of such objects. 相似文献
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Luminous accreting stellar mass and supermassive black holes produce power–law continuum X-ray emission from a compact central corona. Reverberation time lags occur due to light travel time delays between changes in the direct coronal emission and corresponding variations in its reflection from the accretion flow. Reverberation is detectable using light curves made in different X-ray energy bands, since the direct and reflected components have different spectral shapes. Larger, lower frequency, lags are also seen and are identified with propagation of fluctuations through the accretion flow and associated corona. We review the evidence for X-ray reverberation in active galactic nuclei and black hole X-ray binaries, showing how it can be best measured and how it may be modelled. The timescales and energy dependence of the high-frequency reverberation lags show that much of the signal is originating from very close to the black hole in some objects, within a few gravitational radii of the event horizon. We consider how these signals can be studied in the future to carry out X-ray reverberation mapping of the regions closest to black holes. 相似文献
4.
Here we consider our universe as homogeneous spherically symmetric FRW model and analyze the thermodynamics of this model
of the universe in scalar-tensor theory. Assuming the first law of thermodynamics validity of the generalized second law of
thermodynamics (GSLT) at the event horizon is examined in both the cases when the universe is filled with perfect fluid and
the holographic dark energy. 相似文献
5.
Sanjay Sarkar 《Astrophysics and Space Science》2014,352(2):859-866
The present work deals with the accretion of two minimally interacting fluids: dark matter and a hypothetical isotropic fluid as the holographic dark energy components onto black hole and wormhole in a spatially homogeneous and anisotropic Bianchi type-V universe. To obtain an exact solution of the Einstein’s field equations, we use the assumption of linearly varying deceleration parameter. Solution describes effectively the actual acceleration and indicates a big rip type future singularity of the universe. We have studied the evolution of the mass of black hole and the wormhole embedded in this anisotropic universe in order to reproduce a stable universe protected against future-time singularity. It is observed that the accretion of these dark components leads to a gradual decrease and increase of black hole and wormhole mass respectively. Finally, we have found that contrary to our previous case (Sarkar in Astrophys. Space. Sci. 341:651, 2014a), the big rip singularity of the universe with a divergent Hubble parameter of this dark energy model may be avoided by a big trip. 相似文献
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The interaction of modified holographic dark energy and dark matter with varying G in flat Kaluza Klein universe is considered. Further, we take infrared cutoff scale L as future event horizon. In this scenario, equations of state parameter as well as evolution are explored. We also check
the validity of the generalized second law of thermodynamics. It is interesting to mention here that our results show consistency
with the present observations. 相似文献
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This paper is aimed to investigate 5D holographic dark energy (HDE) in DGP-Brane cosmology by employing a combination of Sne Ia, BAO and CMB observational data and constraining cosmological parameters. The FRW dynamics for the normal branch (?=+1) solution of induced gravity brane-world model is taken with the assumption that matter in 5D bulk is HDE such that its holographic nature is reproduced effectively in 4D universe. In the HDE model, we used Hubble horizon as IR cutoff instead of future event horizon. This way, while the model predicts current universe acceleration, it also removes the problem of circular reasoning and causality observed in using future event horizon as IR cutoff. 相似文献
8.
Apparent horizon and event horizon thermodynamics of?a?Vaidya?black hole using Damour-Ruffini method
Using Damour-Ruffini method, Hawking radiation from the apparent horizon of a Vaidya black hole is calculated. The thermodynamics
can be built successfully on the apparent horizon. In the meantime, when a time-dependent perturbation is given to the apparent
horizon, the first law of thermodynamics can also be constructed successfully at a new supersurface near the apparent horizon.
The expressions of the characteristic position and temperature are consistent with the previous results. It is concluded that
the thermodynamics should be constructed on the apparent horizon exactly while the event horizon thermodynamics is just one
of the perturbations near the apparent horizon. These conclusions can be regarded as providing some new evidences for our
previous viewpoint. 相似文献
9.
Antonio Pasqua A. Khodam-Mohammadi Mubasher Jamil R. Myrzakulov 《Astrophysics and Space Science》2012,340(1):199-208
Motivated by the holographic principle, it has been suggested that the dark energy density may be inversely proportional to the area A of the event horizon of the universe. However, such a model would have a causality problem. In this work, we consider the entropy-corrected version of the holographic dark energy model in the non-flat FRW universe and we propose to replace the future event horizon area with the inverse of the Ricci scalar curvature. We obtain the equation of state (EoS) parameter ω Λ, the deceleration parameter q and WD￠\Omega_{D}' in the presence of interaction between Dark Energy (DE) and Dark Matter (DM). Moreover, we reconstruct the potential and the dynamics of the tachyon, K-essence, dilaton and quintessence scalar field models according to the evolutionary behavior of the interacting entropy-corrected holographic dark energy model. 相似文献
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Using the analytic extension method, we study Hawking radiation of an (n+4)-dimensional Schwarzschild-de Sitter black hole. Under the condition that the total energy is conserved, taking the reaction of the radiation of particles to the spacetime into consideration and considering the relation between the black hole event horizon and cosmological horizon, we obtain the radiation spectrum of de Sitter spacetime. This radiation spectrum is no longer a strictly pure thermal spectrum. It is related to the change of the Bekenstein-Hawking (B-H) entropy corresponding the black hole event horizon and cosmological horizon. The result satisfies the unitary principle. At the same time, we also testify that the entropy of de Sitter spacetime is the sum of the entropy of black hole event horizon and the one of cosmological horizon. 相似文献
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We present results from a numerical study of the runaway instability of thick discs around black holes. This instability is an important issue for most models of cosmic gamma-ray bursts, where the central engine responsible for the initial energy release is such a system consisting of a thick disc surrounding a black hole. We have carried out a comprehensive number of time-dependent simulations aimed at exploring the appearance of the instability. Our study has been performed using a fully relativistic hydrodynamics code. The general relativistic hydrodynamic equations are formulated as a hyperbolic flux-conservative system and solved using a suitable Godunov-type scheme. We build a series of constant angular momentum discs around a Schwarzschild black hole. Furthermore, the self-gravity of the disc is neglected and the evolution of the central black hole is assumed to be that of a sequence of exact Schwarzschild black holes of varying mass. The black hole mass increase is thus determined by the mass accretion rate across the event horizon. In agreement with previous studies based on stationary models, we find that by allowing the mass of the black hole to grow the disc becomes unstable. Our hydrodynamical simulations show that for all disc-to-hole mass ratios considered (between 1 and 0.05), the runaway instability appears very fast on a dynamical time-scale of a few orbital periods, typically a few 10 ms and never exceeding 1 s for our particular choice of the mass of the black hole (2.5 M-3 M-1 ) . The implications of our results in the context of gamma-ray bursts are briefly discussed. 相似文献
12.
Atreyee Biswas 《Astrophysics and Space Science》2018,363(10):203
The present work deals with irreversible thermodynamics of universe containing interacting dark fluids. Recent observational evidences reveal that the universe is dominated by two dark components-dark matter and dark energy. The interaction between them leads to spontaneous heat flow between the horizon and the fluid system and as a result the system will no longer be in thermal equilibrium. In this paper dark matter is chosen as pressureless dust while modified Chaplygin gas has been considered as dark energy. In two separate cases we have considered the universe to be bounded by apparent horizon and event horizon and the validity of generalized second law of thermodynamics in the context of irreversible thermodynamics has been studied for both the cases. 相似文献
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We study a black hole in an expanding Universe during the radiation-dominated stage. In particular, such a black hole may be of the primordial origin. In the case when the black hole radius is much smaller than the cosmological horizon, we found a self-consistent solution for the metric and the matter distribution and its velocity far from the black hole. At distances much smaller than the cosmological horizon our solution coincides with the previously obtained solution for quasi-stationary accretion. Our results can be applied, in particular, for the formation of dark matter density spikes around primordial black holes, and for the evolution of dark matter clumps during the radiation-dominated stage. 相似文献
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We obtain renormalized stress tensor of a mass-less, charge-less dynamical quantum scalar field, minimally coupled with a spherically symmetric static Lukewarm black hole. In two dimensional analog the minimal coupling reduces to the conformal coupling and the stress tensor is found to be determined by the nonlocal contribution of the anomalous trace and some additional parameters in close relation to the work presented by Christensen and Fulling. Lukewarm black holes are a special class of Reissner-Nordström-de Sitter space times where its electric charge is equal to its mass. Having the obtained renormalized stress tensor we attempt to obtain a time-independent solution of the well known metric back reaction equation. Mathematical derivations predict that the final state of an evaporating quantum Lukewarm black hole reduces to a remnant stable mini black hole with moved locations of the horizons. Namely the perturbed black hole (cosmological) horizon is compressed (extended) to scales which is smaller (larger) than the corresponding classical radius of the event horizons. Hence there is not obtained an deviation on the cosmic sensor-ship hypothesis. 相似文献
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Dynamical behaviour of an evaporating black hole is investigated for a Vaidya-type metric. The Raychaudhuri equation is examined with including terms up to the second order in the luminosity near the event horizon. Such a solution is found that the luminosity increases as the mass decreases during the evaporation. 相似文献
16.
There has been a renewed interest in the recent years in the possibility of deviations from the predictions of Newton’s “inverse-square
law” of universal gravitation. One of the reasons for renewing this interest lies in various theoretical attempts to construct
a unified elementary particle theory, in which there is a natural prediction of new forces over macroscopic distances. Therefore
the existence of such a force would only coexist with gravity, and in principle could only be detected as a deviation from
the inverse square law, or in the “universality of free fall” experiments. New experimental techniques such that of Sagnac
interferometry can help explore the range of the Yukawa correction λ≥1014 m where such forces might be present. It may be, that future space missions might be operating in this range which has been
unexplored for very long time. In this paper we derive the basic thermodynamic parameters of such a Yukawa stationary spherically
symmetric black hole. First, the expression for the event horizon of such a black hole is derived, with the help of which
the temperature, entropy and heat capacity of this particular black hole are obtained. We have also obtained analytical expressions
for the change of mass of such black hole, and also its corresponding evaporation time. 相似文献
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用在brick模型基础上发展起来的membrane模型 ,计算了缘于任意自旋场的非静态黑洞———Vaidya黑洞的自由能和熵。结果表明 ,玻色子场 (自旋s =1,2 )和费米子场 (自旋s =1/2 )的熵都恰好与黑洞的视界面积成正比 ,这与静态和稳态的情况相同。而且 ,玻色子和费米子场的熵具有相同的形式 ,二者相差一个系数 相似文献
19.
Sumanta Chakraborty 《Astrophysics and Space Science》2013,347(2):411-421
The general misconception regarding velocity measurements of a test particle as it approaches black hole is addressed by introducing generalized observer set. For a general static spherically symmetric metric applicable to both Einstein and alternative gravities as well as for some well known solutions in alternative gravity theories, we find that velocity of the test particle do not approach that of light at event horizon by considering ingoing observers and test particles. 相似文献
20.
Hawking effect from a dynamical Kerr black hole is investigated using the improved Damour-Ruffini method with a new tortoise
coordinate transformation. Hawking temperature of the black hole can be obtained point by point at the event horizon. It is
found that Hawking temperatures of different points on the surface are different. Moreover, the temperature does not turn
to zero while the dynamical black hole turns to an extreme one. 相似文献