We investigate the consequences for the black hole area of introducing fractal structure for the horizon geometry. We create a three-dimensional spherical analogue of a 'Koch Snowflake' using a infinite diminishing hierarchy of touching spheres around the Schwarzschild event horizon. We can create a fractal structure for the horizon with finite volume and infinite (or finite) area. This is a toy model for the possible effects of quantum gravitational spacetime foam, with significant implications for assessments of the entropy of black holes and the universe, which is generally larger than in standard picture of black hole structure and thermodynamics, potentially by very considerable factors. The entropy of the observable universe today becomes log(S) is approximately 120(1+D/2) with D = 0 for a smooth spacetime structure and D = 1 for the most intricate. The Hawking lifetime of black holes is also reduced.
It has been argued that the strong cosmic censorship conjecture is violated by Reissner-Nordström-de Sitter black holes: for near-extremal black holes, generic scalar field perturbations arising from smooth initial data have finite energy at the Cauchy horizon even though they are not continuously differentiable there. In this paper, we consider the analogous problem for coupled gravitational and electromagnetic perturbations. We find that such perturbations exhibit a much worse violation of strong cosmic censorship: for a sufficiently large near-extremal black hole, perturbations arising from…
We investigate the area spectrum for rotating black holes which are Kerr and BTZ black holes. For slowly rotating black holes, we use the Maggiore's idea combined with Kunstatter's method to derive their area spectra, which are equally spaced.
Black hole thermodynamics suggests that a black hole should have an entropy given by a quarter of the area of its horizon. Earlier calculations in U(1) loop quantum gravity have led to a dominant term proportional to the area, but there was a correction involving the logarithm of the area. We find however that SU(2) loop quantum gravity can provide an entropy that is strictly proportional to the area as expected from black hole thermodynamics.
The assimilation of a quantum (finite size) particle by a Reissner-Nordström black hole inevitably involves an increase in the black-hole surface area. It is shown that this increase can be minimized if one considers the capture of the lightest charged particle in nature. The unavoidable area increase is attributed to two physical reasons: the Heisenberg quantum uncertainty principle and a Schwinger-type charge emission (vacuum polarization). The fundamental lower bound on the area increase is $4 \hbar$, which is smaller than the value given by Bekenstein for neutral particles. Thus, this proc…
Since the Bekenstein's proposal that a black hole has equally spaced area spectrum, the quasinormal modes as the characteristic modes of a black hole have been used in obtaining the horizon area spectrum of the black hole. However, the area spectrum of the Kerr black hole in some previous works was inconsistent with the Bekenstein's proposal. In this paper, we notice that the Kerr black hole has three types of resonance modes which are quasinormal modes (QNM), total transmission modes (TTM), and total reflection modes (TRM). All of these resonances represent highly damped oscillations and only…
We consider the possibility that the horizon area is expressed by the general area spectrum in loop quantum gravity and calculate the black hole entropy by counting the degrees of freedom in spin-network states related to its area. Although the general area spectrum has a complex expression, we succeeded in obtaining the result that the black hole entropy is proportional to its area as in previous works where the simplified area formula has been used. This gives new values for the Barbero-Immirzi parameter ($γ=0.5802... \mathrm{or} 0.7847...$) which are larger than that of previous works.
Christodoulou and Rovelli have shown that black holes have large interiors that grow asymptotically linearly in advanced time, and speculated that this may be relevant to the information loss paradox. We show that there is no simple relation between the interior volume of an arbitrary black hole and its horizon area. That is, the volume enclosed is not necessarily a monotonically increasing function of the surface area.
We clarify the relation between gravitational entropy and the area of horizons. We first show that the entropy of an extreme Reissner-Nordström black hole is $zero$, despite the fact that its horizon has nonzero area. Next, we consider the pair creation of extremal and nonextremal black holes. It is shown that the action which governs the rate of this pair creation is directly related to the area of the acceleration horizon and (in the nonextremal case) the area of the black hole event horizon. This provides a simple explanation of the result that the rate of pair creation of non-extreme black…
In the framework of tunneling mechanism and employing Bekenstein's general expression for the variation of the black hole area, we determine the area quantum up to a constant. Depending on the value of this constant one can get either Bekenstein's lower bound or Hod's one for the change in the black hole area.
Whereas the usual understanding is that the entropy of only a non-extremal black hole is given by the area of the horizon, there are derivations of an area law for extremal black holes in some model calculations. It is explained here how such results can arise in an approach where one sums over topologies and imposes the extremality condition after quantization.
A conjecture by Hod states that for the black hole horizon the spacing of its area spectrum is determined by the asymptotic value of its quasinormal frequencies. Recently to overcome some difficulties, Maggiore proposes some changes to the original Hod's conjecture. Taking into account the modifications proposed by Maggiore we calculate the area spectrum of the d-dimensional Reissner-Nordstrom black hole in the small charge limit.
With the new physical interpretation of quasinormal modes proposed by Maggiore, the quantum area spectra of black holes have been investigated recently. Adopting the modified Hod's treatment, results show that the area spectra for black holes are equally spaced and the spacings are in a unified form, $\triangle A=8π\hbar$, in Einstein gravity. On the other hand, following Kunstatter's method, the studies show that the area spectrum for a nonrotating black hole with no charge is equidistant. And for a rotating (or charged) black hole, it is also equidistant and independent of the angular moment…
The recent proposal of Maggiore that the periodicity of a black hole may be the origin of area quantization law is analyzed in the context of three dimensional black holes. We use the period of motion of an outgoing wave which is shown to be related to the vibrational frequency of the perturbed black hole, to quantize the horizon area of rotating and non-rotating BTZ black holes. It is shown that the equally spaced area spectrum takes the same form as the obtained in the literature using the quasinormal mode analysis for both metrics. Using this method, we do not need to use the small angular …
Various approaches to black hole entropy yield the area law with logarithmic corrections, many involving a coefficient 1/2, and some involving 3/2. It is pointed out here that the standard quantum geometry formalism is not consistent with 3/2 and favours 1/2.
The black hole area theorem implies that when two black holes merge, the area of the final black hole should be greater than the sum of the areas of the two original black holes. We examine how this prediction can be tested with gravitational-wave observations of binary black holes. By separately fitting the early inspiral and final ringdown stages, we calculate the posterior distributions for the masses and spins of the two initial and the final black holes. This yields posterior distributions for the change in the area and thus a statistical test of the validity of the area increase law. We …
We investigate highly damped quasinormal modes of regular black hole coupled to nonlinear electrodynamics. Using the WKB approximation combined with complex-integration technique, we show that the real part of the frequency disappears in the highly damped limit. If we use the Bohr's correspondence principle, the area spectrum of this black hole is continuous. We discuss its implication in the loop quantum gravity.
We emphasize the importance of the Voros product in defining a noncommutative inspired Reissner-Nordström black hole. The entropy of this black hole is then computed in the tunneling approach and is shown to obey the area law at the next to leading order in the noncommutative parameter $θ$. Modifications to entropy/area law is then obtained by going beyond the semi-classical approximation. The leading correction to the semiclassical entropy/area law is found to be logarithmic and its coefficient involves the noncommutative parameter $θ$.
We study the existence and stability of isoperimetric surfaces in a family of rotating black holes in New Massive Gravity. We show that the stability of such surfaces is determined by the sign of the hair parameter. We use the isoperimetric surfaces to find a geometric inequality between the area and the angular momentum of the black hole, conjecturing geometric inequalities for more general black holes.
The thermodynamic and euclidean functional integral approaches to black hole entropy are discussed. The existence of some freedom in the definition of the entropy is pointed out and the possibility of a departure from the semiclassical expression discussed in the light of quantum corrections. The semiclassical area dependence of the entropy of matter in the background of a black hole is also reviewed and shown to break down in the case of extremal black holes. The cutoff dependence is shown to be different for the extreme dilatonic and Reissner - Nordstrom black holes.
I present a very simplistic toy model for the inflationary paradigm where the size of the universe undergoes a period of exponential growth. The basic assumption I make use of is that black holes might have a quantized area (mass) spectrum with a stable ground state and that the universe has started with a tightly packed collection of these objects alone.
Following Bekenstein's suggestion that the horizon area of a black hole should be quantized, the discrete spectrum of the horizon area has been investigated in various ways. By considering the quasinormal mode of a black hole, we obtain the transition frequency of the black hole, analogous to the case of a hydrogen atom, in the semiclassical limit. According to Bohr's correspondence principle, this transition frequency at large quantum number is equal to classical oscillation frequency. For the corresponding classical system of periodic motion with this oscillation frequency, an action variabl…
A. Ghosh and P. Mitra made the proposal how to explain the area law for the entropy of extreme black holes in some model calculations. I argue that their approach implicitly operates with strongly singular geometries and says nothing about the contribution of regular metrics of extreme black holes into the partition function.
The recent proposal of Maggiore that the periodicity of a black hole may be the origin of area quantization law is analyzed in the context of black holes in string theory. We use the period of motion of an outgoing wave, which is shown to be related to the vibrational frequency of the perturbed black hole, to quantize the horizon areas of a Sen black hole. It is shown that the equally spaced area spectrum takes the same form as the obtained by Zeng et. al. for Schwarzschild and Kerr black holes and the spacing is the same as that obtained through the quasinormal mode frequencies. In order to o…
In this research work, predominantly we acquire area, angular velocity, entropy, surface gravity and Hawking temperature of inner and outer horizons for Kerr-Newman black hole in presence of quintessence. Additionally, we determine area sum, area product, entropy sum and entropy product. We examine that the area product and entropy product are free from mass $M$ but they surly rely upon the angular momentum $J$, charge $q$, spin parameter $a$ and the normalization factor $c$. We monitor that these thermodynamic products are universal. We investigate that the area sum and entropy sum rely upon …
We present an exact expression for the quasinormal modes of acoustic disturbances in a rotating 2+1 dimensional sonic black hole (draining bathtub fluid flow) in the low frequency limit and evaluate the adiabatic invariant proposed by Kunstatter. We also compute,via Bohr-Sommerfeld quantization rule the equivalent area spectrum for this acoustic black hole, and we compute the superradiance phenomena for pure spinning 2+1 black holes.
We study the equal area law and charge-electric potential criticality for the charged Anti-de Sitter black holes. Considering that the black hole charge is a double-valued function of the electric potential, we investigate the equal area law in detail. We find that the equal area law has two different expressions when the thermodynamic quantities are near the critical point and far from the critical point. For these two different cases, we obtain the analytical coexistence curve for the low and high electric potential black hole phases by using these two expressions of the equal area law. Base…
In this letter, we provide an alternative method to study the area spectrum of certain classes of extremal black holes which have near-horizon geometry as warped AdS. We argue that previous methods which are based on the existence of quasinormal modes may not be applicable in the extremal limit. The topology difference of the near-horizon geometry between non-extremal and extremal black holes implies a separate treatment is needed to study the area discreteness in the extremal limit. To be specific, we will study area spectrum of supersymmetric BMPV black holes/black rings and Reissner-Norstro…
Most calculations of black hole entropy in loop quantum gravity indicate a term proportional to the area eigenvalue A with a correction involving the logarithm of A. This violates the additivity of the entropy. An entropy proportional to A, with a correction term involving the logarithm of the classical area k, which is consistent with the additivity of entropy, is derived in both U(1) and SU(2) formulations.
Non-commutative corrections to the classical expression for the fuzzy sphere area are found out through the asymptotic expansion for its heat kernel trace. As an important consequence, some quantum gravity deviations in the luminosity of black holes must appear. We calculate these deviations for a static, spherically symmetric, black-hole with a horizon modeled by a fuzzy sphere. The results obtained could be verified through the radiation of black holes formed in the Large Hadron Collider (LHC).
We argue that a process where a fuzzy space splits in two others can be used to explain the origin of the black hole entropy, and why a "generalized second law of thermodynamics" appears to hold in the presence of black holes. We reach the Bekenstein-Hawking formula from the count of the microstates of a black hole modeled by a fuzzy space. In this approach, a discrete area spectrum for the black hole, which becomes increasingly spaced as the black hole approaches the Planck scale, is obtained. We show that, as a consequence of this, the black hole radiation becomes less and less entropic as t…
We compute the area(or entropy) product formula for a regular black hole derived by Ayón-Beato and García in 1998\cite{abg}. By explicit and exact calculation, it is shown that the entropy product formula of two physical horizons strictly \emph{depends} upon the ADM mass parameter that means it is \emph{not} an universal(mass-independent) quantity. But a slightly more complicated function of event horizon area and Cauchy horizon area is indeed a \emph{mass-independent} quantity. We also compute other thermodynamic properties of the said black hole. We further study the stability of such black …
We compute area (or entropy) product formula for Newman-Unti-Tamburino (NUT) class of black holes. Specifically, we derive the area product of outer horizon and inner horizon (${ \mathcal{H}}^{\pm }$) for Taub-NUT, Euclidean Taub-NUT black hole, Reissner-Nordström--Taub-NUT black hole, Kerr-Taub-NUT black hole and Kerr-Newman-Taub-NUT black hole under the formalism developed very recently by Wu et al. \cite{wu} [PRD 100, 101501(R) (2019)]. The formalism is that a generic four dimensional Taub-NUT spacetime should be described completely in terms of three or four different types of thermodynami…
We consider the area and entropy spectra of black holes in topologically massive gravity with gravitational Chern-Simons term. The examples we consider are the BTZ black hole and the warped AdS black hole. For the non-rotating BTZ black hole, the area and entropy spectra are equally spaced and independent of the coupling constant $\v$ of the Chern-Simons term. For the rotating BTZ black hole case, the spectra of the inner and outer horizon areas are not equally spaced in general and dependent of the coupling constant $\v$. However the entropy spectrum is equally spaced and independent of the c…
We investigate highly damped quasinormal mode of single-horizon black holes motivated by its relation to the loop quantum gravity. Using the WKB approximation, we show that the real part of the frequency approaches the value $T_{\rm H}\ln 3$ for dilatonic black hole as conjectured by Medved et al. and Padmanabhan. It is surprising since the area specrtum of the black hole determined by the Bohr's correspondence principle completely agrees with that of Schwarzschild black hole for any values of the electromagnetic charge or the dilaton coupling. We discuss its generality for single-horizon blac…
Gravitational radiation is locally defined where the wavefronts are roughly spherical. A local energy tensor is defined for the gravitational radiation. Including this energy tensor as a source in the truncated Einstein equations describes gravitational radiation reaction, such as back-reaction on a roughly spherical black hole. The energy-momentum in a canonical frame is covariantly conserved. The strain to be measured by a distant detector is simply defined.
We present explicit results for the product of all horizon areas for general rotating multi-charge black holes, both in asymptotically flat and asymptotically anti-de Sitter spacetimes in four and higher dimensions. The expressions are universal, and depend only on the quantized charges, quantized angular momenta and the cosmological constant. If the latter is also quantized these universal results may provide a "looking glass" for probing the microscopics of general black holes.
Using a graphical analysis, we show that for the horizon radius $r_h\gtrsim 4.8\sqrtθ$, the standard semiclassical Bekenstein-Hawking area law for noncommutative Schwarzschild black hole exactly holds for all orders of $θ$. We also give the corrections to the area law to get the exact nature of the Bekenstein-Hawking entropy when $r_h<4.8\sqrtθ$ till the extremal point $r_h=3.0\sqrtθ$.
We derive various important thermodynamic relations of the inner and outer horizon in the background of Taub-NUT(Newman-Unti-Tamburino) black hole in four dimensional \emph{Lorentzian geometry}. We compare these properties with the properties of Reissner Nordstrøm black hole. We compute \emph{area product, area sum, area minus and area division} of black hole horizons. We show that they all are not universal quantities. Based on these relations, we compute the area bound of all horizons. From area bound, we derive entropy bound and irreducible mass bound for both the horizons. We further study…
We show the importance of the Voros product in defining a noncommutative Schwarzschild black hole. The corrected entropy/area-law is then computed in the tunneling formalism. Two types of corrections are considered; one, due to the effects of noncommutativity and the other, due to the effects of going beyond the semiclassical approximation. The leading correction to the semiclassical entropy/area-law is logarithmic and its coefficient involves the noncommutative parameter.
A classical black hole is characterized by a horizon that absorbs radiation of all frequencies incident on it. Perturbation of these black holes is well-understood via exponentially damped sinusoids known as quasi-normal modes. Any departure from such classical behavior near the horizon may induce significant modifications in the late time evolution of the perturbation leading to so-called gravitational wave echoes. This work considers the effect of black hole area-quantization on the formation of gravitational wave echoes. We investigate how the resulting echo waveform may depend on various m…
We investigate a holographic version of Maxwell's equal area law analogous to that for the phase transition in the black hole temperature/black hole entropy plane of a charged AdS black hole. We consider proposed area laws for both the black hole temperature/holographic entanglement entropy plane and the black hole temperature/2-point correlation function plane. Despite recent claims to the contrary, we demonstrate numerically that neither proposal is valid. We argue that there is no physical reason to expect such a construction in these planes.
We have shown that the dynamics of the scalar field $ϕ(x)= ``G^{-1}(x)"$ in Brans-Dicke theories of gravity makes the surface area of the black hole horizon {\it oscillatory} during its dynamical evolution. It explicitly explains why the area theorem does not hold in Brans-Dicke theory. However, we show that there exists a certain non-decreasing quantity defined on the event horizon which is proportional to the black hole entropy for the case of stationary solutions in Brans-Dicke theory. Some numerical simulations have been demonstrated for Oppenheimer-Snyder collapse in Brans-Dicke theory.
It is known that, in the noncommutative Schwarzschild black hole spacetime, the point-like object is replaced by the smeared object, whose mass density is described by a Gaussian distribution of minimal width $\sqrtθ$ with $θ$ the noncommutative parameter. The elimination of the point-like structures makes it quite different from the conventional Schwarzschild black hole. In this paper, we mainly investigate the area spectrum and entropy spectrum for the noncommutative Schwarzschild black hole with $0\leq θ\leq (\frac{M}{1.90412})^{2}$. By the use of the new physical interpretation of the quas…
Extremal rotating black holes in Einstein-Maxwell theory feature two branches. On the branch emerging from the Myers-Perry solutions their angular momentum is proportional to their horizon area, while on the branch emerging from the Tangherlini solutions their angular momentum is proportional to their horizon angular momentum. The transition between these branches occurs at a critical value of the charge, which depends on the value of the angular momentum. However, when a dilaton is included, the angular momentum is always proportional to the horizon area.
The Rényi and Tsallis entropies are discussed as possible alternatives to the Bekenstein-Hawking area-law entropy. It is pointed out how replacing the entropy notion, but not the Hawking temperature and the thermodynamical energy may render the whole black hole thermodynamics inconsistent. The possibility to relate the Rényi and Tsallis entropies with the quantum gravity corrected Bekenstein-Hawking entropy is discussed.
Since the Bekenstein's proposal that a black hole has equally spaced area spectrum, the quasinormal modes as the characteristic modes of a black hole have been used in obtaining the horizon area spectrum of the black hole. However, the area spectrum of the Kerr black hole in some previous works was inconsistent with the Bekenstein's proposal. In this paper, noting that black holes can have three types of resonance modes which are quasinormal modes (QNM), total transmission modes (TTM), and total reflection modes (TRM), we propose that all of these modes in highly damped regime should be used i…
We demonstrate that an equidistant area spectrum for the link variables in loop quantum gravity can reproduce both the thermodynamics and the quasinormal mode properties of black holes.
During the last twenty-five years evidence has been mounting that a black-hole surface area has a {\it discrete} spectrum. Moreover, it is widely believed that area eigenvalues are {\it uniformally} spaced. There is, however, no general agreement on the {\it spacing} of the levels. In this letter we use Bohr's correspondence principle to provide this missing link. We conclude that the area spacing of a black-hole is $4\hbar \ln 3$. This is the unique spacing consistent both with the area-entropy {\it thermodynamic} relation for black holes, with Boltzmann-Einstein formula in {\it statistical p…
Motivated by the recent work on a new physical interpretation of quasinormal modes by Maggiore, we utilize this new proposal to the interesting case of Kerr black hole. In particular, by modifying Hod's idea, the resulting black hole horizon area is quantized and the resulting area quantum is in full agreement with Bekenstein's result. Furthermore, in an attempt to show that the area spectrum is equally spaced, we follow Kunstatter's method. We propose a new interpretation as a result of Maggiore's idea, for the frequency that appears in the adiabatic invariant of a black hole. The derived are…
Gravitational-wave astronomy has the potential to substantially advance our knowledge of the cosmos, from the most powerful astrophysical engines to the initial stages of our universe. Gravitational waves also carry information about the nature of black holes. Here we investigate the potential of gravitational-wave detectors to test a proposal by Bekenstein and Mukhanov that the area of black hole horizons is quantized in units of the Planck area. Our results indicate that this quantization could have a potentially observable effect on the classical gravitational wave signals received by detec…
Motivated by the recent work about a new physical interpretation of quasinormal modes by Maggiore, we investigate the quantization of near-extremal Schwarzschild-de Sitter black holes in the four dimensional spacetime. Following Kunstatter's method, we derive the area and entropy spectrum of near-extremal Schwarzschild-de Sitter black holes which differs from Setare's result. Furthermore, we find that the derived a universal area spectrum is $2πn$ which is equally spaced.
The inequality between area and charge $A\geq 4πQ^2$ for dynamical black holes is proved. No symmetry assumption is made and charged matter fields are included. Extensions of this inequality are also proved for regions in the spacetime which are not necessarily black hole boundaries.
Neutron stars exhibit a set of universal relations independent of their equation of state that bears semblance to the black hole no hair relations. Motivated by this, we analytically and numerically explore other relations that connect neutron star and black hole universality. By analyzing two different measures, we find that certain rescaled entropies possess a nearly universal behavior. We also discover that when the compactness of neutron stars approaches the black hole limit, the rescaled entropy approaches that of a black hole, and the thermodynamic entropy scales with the stellar surface…
Motivated by Maggiore's new interpretation of quasinormal modes, starting from the first law of thermodynamics of black holes, we investigate area spectra of a near extremal Schwarzschild de sitter black hole and a higher dimensional near extremal Reissner-Nordstrom de sitter black hole. We show that the area spectra of all these black holes are equally spaced and irrelevant to the parameters of black holes.
Simple arguments related to the entropy of black holes strongly constrain the spectrum of the area operator for a Schwarzschild black hole in loop quantum gravity. In particular, this spectrum is fixed completely by the assumption that the black hole entropy is maximum. Within the approach discussed, one arrives in loop quantum gravity at a quantization rule with integer quantum numbers $n$ for the entropy and area of a black hole.
We prove that for sub-extremal axisymmetric and stationary black holes with arbitrary surrounding matter the inequality $8π|J|<A$ holds, where $J$ is the angular momentum and $A$ the horizon area of the black hole.
Motivated by the recent interest in quantization of black hole area spectrum, we consider the area spectrum of Kerr and extremal Kerr black holes. Based on the proposal by Bekenstein and others that the black hole area spectrum is discrete and equally spaced, we implement Kunstatter's method to derive the area spectrum for the Kerr and extremal Kerr black holes. The real part of the quasinormal frequencies of Kerr black hole used for this computation is of the form $mΩ$ where $Ω$ is the angular velocity of the black hole horizon. The resulting spectrum is discrete but not as expected uniformly…
