Triple points and phase transitions of D-dimensional dyonic Ad S black holes with quasitopological electromagnetism in Einstein–Gauss–Bonnet gravity

By considering the negative cosmological constant Λ as a thermodynamic pressure, we study the thermodynamics and phase transitions of the D-dimensional dyonic Ad S black holes(BHs) with quasitopological electromagnetism in Einstein–Gauss–Bonnet(EGB) gravity. The results indicate that the small/large BH phase transition that is similar to the van der Waals(vdW) liquid/gas phase transition always exists for any spacetime dimensions. Interestingly, we then find that this BH system exhibits a more complex phase structure in 6-dimensional case that is missed in other dimensions.Specifically, it shows for D = 6 that we observed the small/intermediate/large BH phase transitions in a specific parameter region with the triple point naturally appeared. Moreover, when the magnetic charge turned off, we still observed the small/intermediate/large BH phase transitions and triple point only in 6-dimensional spacetime, which is consistent with the previous results. However, for the dyonic Ad S BHs with quasitopological electromagnetism in Einstein–Born–Infeld(EBI) gravity, the novel phase structure composed of two separate coexistence curves observed by Li et al. [Phys. Rev. D105 104048(2022)] disappeared in EGB gravity. This implies that this novel phase structure is closely related to gravity theories, and seems to have nothing to do with the effect of quasitopological electromagnetism. In addition, it is also true that the critical exponents calculated near the critical points possess identical values as mean field theory. Finally, we conclude that these findings shall provide some deep insights into the intriguing thermodynamic properties of the dyonic Ad S BHs with quasitopological electromagnetism in EGB gravity.

Supermassive Primordial Black Holes for Nano-Hertz Gravitational Waves and High-redshift JWST Galaxies

Recently,observational hints for supermassive black holes have been accumulating,prompting the question:Can primordial black holes(PBHs)be supermassive,particularly with masses M■10^(9)M_(⊙)?A supercritical bubble,containing an inflating baby universe,that nucleated during inflation can evolve into a PBH in our observable universe.We find that when the inflaton slowly transitions past a neighboring vacuum,the nucleation rate of supercritical bubbles inevitably peaks,leading to a mass distribution of multiverse PBHs with a peak mass up to M■10^(11)M_(⊙).Thus,our mechanism naturally provides a primordial origin for supermassive black holes.

Generalized Newton’s Theory of Universal Gravitation and Black Holes

The Newton’s theory of universal gravitation is generalized. Significantly strong at short distances central interaction of bodies and particles is established in comparison with Newtonian. A connection is found with Black Holes, with the horizon of events. Possibility of systematization of all Black Holes is shown. An illustration is given on the example of Black Hole SgrA*.

Quantum Unruh Effect on Radiation of Black Holes

The quantum Unruh effect on radiation of a gravitational object including a black hole is analyzed and calculated. It is surprisingly found that the well-known Hawking radiation of a black hole is not physical. Applying the Stephan-Boltzmann law with the use of the Unruh radiation temperature at the surface of a black hole to calculate the power of radiation of the black hole is conceptually unphysical. This is because the Unruh radiation temperature results from the gravitational field of the object rather than from the thermal motion of matter of the object, so that the Stephan-Boltzmann law is not applicable. This paper shows that the emission power of Unruh radiation from a gravitational object should be calculated in terms of the rate of increase of the total Unruh radiation energy outside the object. The result obtained from this study indicates that a gravitational object can emit Unruh radiation when the variation of its mass and radius satisfies an inequality of dM/M > 1.25dR/R. For a black hole, the emission of Unruh radiation does not occur unless it can loose its mass (dM < 0). The emission power of Unruh radiation is only an extremely tiny part of the rate of mass-energy loss if the black hole is not extremely micro-sized. This study turns down our traditional understanding of the Hawking radiation and thermodynamics of black holes.

Vibration Reduction by a Partitioned Dynamic Vibration Absorber with Acoustic Black Hole Features

Vibration quality is a vital indicator for assessing the progress of modern equipment.The dynamic vibration absorber(DVA)based on the acoustic black hole(ABH)feature is a new passive control method that manipulates waves.It offers efficient energy focalization and broad-spectrum vibration suppression,making it highly promising for applications in large equipment such as aircraft,trains,and ships.Despite previous advancements in ABH-DVA development,certain challenges remain,particularly in ensuring effective coupling with host structures during control.To address these issues,this study proposes a partitioned ABH-featured dynamic vibration absorber(PABH-DVA)with partitions in the radial direction of the disc.By employing a plate as the host structure,simulations and experiments were conducted,demonstrating that the PABH-DVA outperforms the original symmetric ABH-DVA in terms of damping performance.The study also calculated and compared the coupling coefficients of the two ABH-DVAs to uncover the mechanism behind the enhanced damping.Simulation results revealed that the PABH-DVA exhibits more coupled modes,occasionally with lower coupling coefficients than the symmetric ABH-DVA.The influence of frequency ratio and modal mass was further analyzed to explain the reasons behind the PABH-DVA's superior damping performance.Additionally,the study discussed the impact of the number of slits and their orientation.This research further explains the coupling mechanism between the ABH-DVA and the controlled structure,and provides new ideas for the further application of ABH in engineering.

A simpler method for researching fermions tunneling from black holes

A new simpler mathematic method is proposed to study fermions tunneling from black holes. According to this method, by using semiclassical approximation theory, it simplifies the Dirac equation of curved spacetime and then the relationship of the gamma matrix and the component of contravariant metric is considered in order to transform the set of difficult quantum equations into a simple equation. Finally, the fermion tunneling and Hawking radiation of black holes are obtained. The method is very effective and simple, and we will take the Schwarzschild black hole with global monopole and the higher-dimensional Reissner-Nordstrom de Sitter black hole as two examples to show the fact.

How is a black hole created from nothing?

Using the synchronous coordinates,the creation of a Schwarzschild black hole immersed in a de Sitter spacetime can be viewed as a coherent creation of a collection of timelike geodesics.The previously supposed conical singularities do not exist at the horizons of the constrained instanton.Instead,the unavoidable irregularity is presented as a nonvanishing second fundamental form elsewhere at the quantum transition 3-surface.The same arguments can be applied to charged,topological,or higher dimensional black hole cases.

View of thermodynamic phase transition of the charged Gauss-Bonnet AdS black hole via the shadow

We examine thermodynamic phase transition(PT)of the charged Gauss-Bonnet Ad S black hole(BH)by utilizing the shadow radius.In this system,we rescale the corresponding Gauss-Bonnet coefficientαby a factor of 1/(D-4),and ensure thatαis positive to avoid any singularity problems.The equation derived for the shadow radius indicates that it increases as the event horizon radius increases,making it an independent variable for determining BH temperature.By investigating the PT curve in relation to shadows,we can observe that the shadow radius can be used as an alternative to the event horizon radius in explaining the phenomenon of BH PT.Furthermore,the results indicate that an increase in the parameterαcorresponds to a decrease in the temperature of the BH.By utilizing the relationship between the temperature and the shadow radius,it is possible to obtain the thermal profile of the Gauss-Bonnet AdS BH.It is evident that there is an N-type variation in temperature for pressures P<P_(c).Additionally,as the parameterαincreases,the region covered by shadow expands while the temperature decreases.The utilization of BH shadows as a probe holds immense significance in gaining a deeper understanding of BH thermodynamic behavior.

Thermodynamics in a quantum corrected Reissner-Nordstr?m-AdS black hole and its GUP-corrections

We calculate the thermodynamic quantities in the quantum corrected Reissner-Nordstr?m-AdS(RN-AdS)black hole,and examine their quantum corrections.By analyzing the mass and heat capacity,we give the critical state and the remnant state,respectively,and discuss their consistency.Then,we investigate the quantum tunneling from the event horizon of massless scalar particle by using the null geodesic method,and charged massive boson W^(±)and fermions by using the Hamilton-Jacob method.It is shown that the same Hawking temperature can be obtained from these tunneling processes of different particles and methods.Next,by using the generalized uncertainty principle(GUP),we study the quantum corrections to the tunneling and the temperature.Then the logarithmic correction to the black hole entropy is obtained.

Timing and Spectral Analysis of the Black Hole X-Ray Binary MAXI J1803-298 with Insight-HXMT Data

We present a comprehensive analysis of the 2021 outburst of MAXI J1803–298 utilizing observations of the Insight-Hard X-ray Modulation Telescope(Insight-HXMT)spanning from the low hard state to the high soft state.Within the Insight-HXMT data set,compared to the previous work,we identify a more prolonged presence of typeC quasi-periodic oscillations(QPOs)with centroid frequencies ranging from~0.16 to 6.3 Hz,which present correlations with the hardness ratio and the photon index of the Comptonized component.For QPO frequencies less than~2 Hz,the QPO phase lags are hard(photons of 10–19 keV arrive later than those of 1–4 keV),while at higher frequencies,the lags become soft at and above~4 Hz.Furthermore,the spectra in all Insight-HXMT observations consist of a multi-color blackbody component and a Comptonized component,as commonly observed in classical black hole X-ray binaries.We analyze state transitions and the evolution of accretion geometry in this work.The fitted inner disk radius increases abnormally during the low hard state,hypothesized to result from the corona condensing onto the inner disk.Additionally,two significant drops in flux are observed during the soft intermediate state,maybe implying changes in the corona/jet and the disk,respectively.

Thermodynamics of charged AdS black hole surrounded by quintessence in restricted phase space

We study thermodynamics of charged AdS black hole surrounded by quintessence in a new formalism which is called the restricted phase space thermodynamics.This context is based on Visser’s holographic thermodynamics with a fixed antide Sitter radius and a variable Newton constant.The conjugate variables,central charge C and the chemical potential m,are introduced as a new pair of thermodynamic variables.We find that the iso-e-charge T-S curve becomes non-monotonic when Q<Q_(c).Correspondingly,the F-T curve exhibits a swallow tail structure.This behavior is considered as a van der Waals-like phase transition.As the value of b related to the energy density of Kiselev’s fluid becomes larger,the critical temperature T_(c)will decrease.Thus,the van derWaals-like phase transition will occur at lower temperature.There is always a non-quilibrium transition from a small unstable black hole to a large stable black hole state in the isocoltage T-S process.There exist a maximum and a Hawking-Page phase transition points in theμ-C plane.As the value of b related to Kiselev’s fluid becomes larger,the Hawking-Page phase transition will occur at lower temperature in the isovoltageμ-T process.For other values of the state parameterω,there also exists van der Waals-like phase transition.

Charged Particles Capture Cross-section by a Weakly Charged Schwarzschild Black Hole

We study the capture cross-section of charged particles by a weakly charged Schwarzschild black hole.The dependence of the maximum impact parameter for capture on the particle’s energy is investigated numerically for different values of the electromagnetic coupling strength between the particle and the black hole.The capture cross-section is then calculated.We show that the capture cross-section is independent of the electromagnetic coupling for ultra-relativistic particles.The astrophysical implications of our results are discussed.

Hawking radiation via tunnelling from general stationary axisymmetric black holes

Hawking radiation is viewed as a tunnelling process. In this way the emission rates of massless particles and massive particles tunnelling across the event horizon of general stationary axisymmetric black holes are calculated, separately. The emission spectra of these two different kinds of outgoing particles have the same functional form and both are consistent with an underlying unitary theory.

A note on the mass of Kerr-AdS black holes in the off-shell generalized ADT formalism

In this note, the off-shell generalized Abbott-Deser-Tekin （ADT） formalism is applied to explore the mass of Kerr- anti-de Sitter （Kerr-AdS） black holes in various dimensions within asymptotically rotating frames. The cases in four and five dimensions are explicitly investigated. It is demonstrated that the asymptotically rotating effect may make the charge non-integrable or unphysical when the asymptotic non-rotating timelike Killing vector associated with the charge is allowed to vary and the fluctuation of the metric is determined by the variation of all the mass and rotation parameters. To obtain a physically meaningful mass, it is proposed that one can let the non-rotating timelike Killing vector be fixed or perform calculations in the asymptotically static frame. The results further support that the ADT formalism is background- dependent.

Concrete quantum tunneling spectrum of Schwarzschild black holes

In this paper,a canonical ensemble model for black hole quantum tunneling radiation is introduced.We find that the probability distribution function is the same as the emission rate of a spherical shell in the Parikh-Wilczek tunneling framework.With this model,the probability distribution function corresponding to the emission shell system is calculated.Therefore,the concrete quantum tunneling spectrum of the Schwarzschild black hole is obtained.

Using “Enhanced Quantization” to Bound the Cosmological Constant, and Computing Quantum Number n for Production of 100 Relic Mini Black Holes in a Spherical Region of Emergent Space-Time

We are looking at comparison of two action integrals and we identify the Lagrangian multiplier as setting up a constraint equation (on cosmological expansion). This is a direct result of the fourth equation of our manuscript which unconventionally compares the action integral of General relativity with the second derived action integral, which then permits Equation (5), which is a bound on the Cosmological constant. What we have done is to replace the Hamber Quantum gravity reference-based action integral with a result from John Klauder’s “Enhanced Quantization”. In doing so, with Padamabhan’s treatment of the inflaton, we then initiate an explicit bound upon the cosmological constant. The other approximation is to use the inflaton results and conflate them with John Klauder’s Action principle for a way, if we have the idea of a potential well, generalized by Klauder, with a wall of space time in the Pre Planckian-regime to ask what bounds the Cosmological constant prior to inflation, and to get an upper bound on the mass of a graviton. We conclude with a redo of a multiverse version of the Penrose cyclic conformal cosmology. Our objective is to show how a value of the rest mass of the heavy graviton is invariant from cycle to cycle. All this is possible due to Equation (4). And we compare all these with results of Reference [1] in the conclusion, while showing its relevance to early universe production of black holes, and the volume of space producing 100 black holes of value about 10^2 times Planck Mass. Initially evaluated in a space-time of about 10^3 Planck length, in spherical length, we assume a starting entropy of about 1000 initially.

Constraining the Earth-mass Primordial Black Hole Mergers Model of the Non-repeating FRBs Using the First CHIME/FRB Catalog

In this paper,we upgrade the constraints for the Earth-mass primordial black hole mergers model based on the first Canadian Hydrogen Intensity Mapping Experiment(CHIME)/fast radio burst(FRB)catalog.Assuming the null hypothesis that the observed non-repeating FRBs originate from Earth-mass primordial black hole mergers,we find that how the charges were distributed in the primordial black hole population is well described by a double powerlaw function with typical charge value of law function with typical charge value of q_(c)/10^(-5)=1.60_(-0.28)^(+0.28),where the power-law index α_(1)=2.33_(-0.18)^(+0.15) for q<q_(c) and α_(2)=4.56_(-0.26)^(+0.30)for q≥q_(c).Here,q represents the charge of the black hole in units of√GM,where M is the mass of the black hole.Furthermore,we infer the local event rate of the bursts is 8.8_(-2.1)^(+5.7)×10^(4)Gpc^(-3) yr^(-1),which indicates that an abundance of the primordial black hole population f■10^(-4) is needed to account for the observed FRBs by CHIME.The results of this paper lay the basis for further research on the electromagnetic radiation background generated by the merger of primordial black hole mergers.

Constraints on individual supermassive binary black holes using observations of PSR J1909-3744

We perform a search for gravitational waves(GWs) from several supermassive binary black hole(SMBBH) candidates(NGC 5548, Mrk 231, OJ 287, PG 1302–102, NGC 4151, Ark 120 and 3C 66B) in long-term timing observations of the pulsar PSR J1909-3744 obtained using the Parkes radio telescope.No statistically significant signals were found. We constrain the chirp masses of those SMBBH candidates and find the chirp mass of NGC 5548 and 3C 66B to be less than 2.4 × 10^9 M⊙ and 2.5 × 10^9 M⊙(with 95% confidence), respectively. Our upper limits remain a factor of 3 to 370 above the likely chirp masses for these candidates as estimated from other approaches. The observations processed here provide upper limits on the GW strain amplitude that improve upon the results from the first Parkes Pulsar Timing Array data release by a factor of 2 to 7. We investigate how information about the orbital parameters can help to improve the search sensitivity for individual SMBBH systems. Finally, we show that these limits are insensitive to uncertainties in the Solar System ephemeris model.

A Novel Derivation of Black Hole Entropy in all Dimensions from Truly Point Mass Sources

It is explicitly shown how the Schwarzschild Black Hole Entropy (in all dimensions) emerges from truly point mass sources at r=0due to a non-vanishing scalar curvature involving the Dirac delta distribution. In order to achieve this, one is required to extend the domain of r to negative values −∞≤r≤+∞. It is the density and anisotropic pressure components associated with the point mass delta function source at the origin r=0which furnish the Schwarzschild black hole entropy in all dimensions D≥4after evaluating the Euclidean Einstein-Hilbert action. Two of the most salient results are i) that the observed spacetime dimension D=4is precisely singled out from all the other dimensions when the strong and weak energy conditions are met, and ii) the point mass source described in this work is not the result of a spherically symmetric gravitational collapse of a star as described by the Oppenheimer-Snyder model because we are not neglecting the pressure. As usual, it is required to take the inverse Hawking temperature βHas the length of the circle Sβ1obtained from a compactification of the Euclidean time in thermal field theory which results after a Wick rotation, it=τ, to imaginary time. This approach can be generalized to the Reissner-Nordstrom and Kerr-Newman metrics. The physical implications of this finding warrant further investigation since it suggests a profound connection between the notion of gravitational entropy and spacetime singularities.

The Calculations of General Relativity on Massive Celestial Bodies Collapsing into Singular Black Holes Are Wrong

Based on general relativity, J. R. Oppenheimer proved that massive celestial bodies may collapse into singular black holes with infinite densities. By analyzing the original paper of Oppenheimer, this paper reveals that the calculations had a series and serious of mistakes. The basic problem is that the calculation supposes that the density of celestial body does not change with space-time coordinates. The density is firstly assumed invariable with space coordinates and then it is assumed invariable with time. But at last, the conclusion that the density of a celestial body becomes infinity is deduced. The premise contradicts with conclusion. In fact, there is no restriction on the initial density and radius for celestial body in the calculation. According to the calculation results of Oppenheimer, a cloud of thin gas may also collapse into singular black hole under the action of gravity. The calculations neglect great rotating speeds of massive and high density celestial bodies which would make them falling apart rather than collapsing into singularities. Because we do not know the function relations that material densities depend on space-time coordinates in advance, there exists the rationality problem of procedure using the Einstein’s equation of gravity field to calculate material collapse. Besides these physical problems, the calculation of Oppenheimer also has some obvious mistakes in mathematics. Another improved method to calculate massive celestial body’s collapse also has similar problems. The results are also unreliable. The conclusion of this paper is that up to now general relativity actually has not proved that massive celestial bodies may collapse into singularity black holes.