Rotation Of Hole Research Articles

Entanglement islands and the Page curve of Hawking radiation for rotating Kerr black holes

We initiate the study of the information paradox of rotating Kerr black holes by employing the recently proposed island rule. It is known that the scalar field theory near the Kerr black hole horizon can be reduced to the two-dimensional effective theory. Working within the framework of the two-dimensional effective theory and assuming the small angular momentum limit, we demonstrate that the entanglement entropy of Hawking radiation from the nonextremal Kerr black hole follows the Page curve and saturates the Bekenstein-Hawking entropy at late times. In addition, we also discuss the effect of the black hole rotation on the Page time and scrambling time. For the extreme Kerr black hole, the entanglement entropy at late times also approximates the Bekenstein-Hawking entropy of the extreme Kerr black hole. These results imply that entanglement islands can provide a semiclassical resolution of the information paradox for rotating Kerr black holes. Published by the American Physical Society 2024

Bondi-Hoyle-Lyttleton accretion around the rotating hairy Horndeski black hole

Modeling of the shock cone formed around a stationary, hairy Horndeski black hole with Bondi-Hoyle-Lyttleton (BHL) accretion has been conducted. We model the dynamical changes of the shock cone resulting from the interaction of matter with the Horndeski black hole, where the scalar field and spacetime have a strong interaction. The effects of the scalar hair, the black hole rotation parameter, and the impacts of the asymptotic speed have been examined, revealing the influence of these parameters on the shock cone and the trapped QPO modes within the cone. Numerical calculations have shown that the hair parameter significantly affects the formation of the shock cone. As the absolute value of the hair parameter increases, the matter in the region of the shock cone is observed to move away from the black hole horizon. The rate of matter expulsion increases as h/M changes. After h/M < -0.6, a visible change in the physical structure of the shock cone occurs, ultimately leading to the complete removal out of the shock cone. On the other hand, it has been revealed that the asymptotic speed significantly affects the formation of the shock cone. As h/M increases in the negative direction and the asymptotic speed increases, the stagnation point moves closer to the black hole horizon. When the value of the hair parameter changes, the rest-mass density of the matter inside the cone decreases, whereas the opposite is observed with the asymptotic speed. Additionally, the formed shock cone has excited QPO modes. The deformation of the cone due to the hair parameter has led to a change or complete disappearance of the QPOs. Meanwhile, at asymptotic speeds of V ∞/c < 0.4, all fundamental frequency modes are formed, while at V ∞/c = 0.4, only the azimuthal mode is excited, and 1:2:3:4:… resonance conditions occur. No QPOs have formed at V ∞/c = 0.6. The results obtained from numerical calculations have been compared with theoretical studies for M87*, and it has been observed that the possible values of h/M found in the numerical simulations are consistent with the theory. Additionally, the results have been compared with those for the GRS 1915+105 black hole, and the hair parameters corresponding to the observed frequencies have been determined.

Five-dimensional Myers-Perry black holes under massive scalar perturbation: bound states and quasinormal modes

The stability of five-dimensional singly rotating Myers-Perry Black Holes against massive scalar perturbations is studied. Both the quasibound states and quasinormal modes of the massive scalar field are considered. For the quasibound states, we use an analytical method to discuss the effective potential felt by the scalar field, and found that there is no potential well outside the event horizon. Thus, singly rotating Myers-Perry Black Holes are stable against the perturbation of quasibound states of massive scalar fields. Then, we use continued fraction method based on solving a seven-term recurrence relations to compute the spectra of the quasinormal modes. For different values of the black hole rotation parameter a, scalar mass parameter μ and angular quantum numbers, all found quasinormal modes are damped. Besides, when the scalar mass μ becomes relatively large, the long-living quasiresonances are also found as in other rotating black hole models. Our results complement previous arguments on the stability of five-dimensional singly rotating Myers-Perry black holes against massive scalar perturbations.

Gravitational lensing by a stable rotating regular black hole

Recent observational data from the Event Horizon Telescope (EHT) collaboration provide convincing realistic evidence for the existence of black hole rotation. From a phenomenological perspective, a recently proposed stable rotating regular (SRR) black hole circumvents the theoretical flaws of the Kerr solution. For the purpose of obtaining observational signatures of this black hole, we study its gravitational lensing effect. In the strong deflection limit, we calculate the deflection angle of light on the equatorial plane, the radius of the photon sphere, and other observables. The observables include the relativistic image position, separation, magnification, and time delays between different images. Then, by modeling M87* and Sgr A* as the SRR black hole, we compute their observables and evaluate the deviation of the observables from the Kerr case. In the weak deflection limit, we calculate the light deflection angle on the equatorial plane of M87* and Sgr A* via the Gauss-Bonnet theorem (GBT). With the growth of deviation parameter e, the gravitational lensing effect in the weak deflection limit intensifies monotonically, and the gravitational lensing effect in the strong deflection limit changes dramatically only at high spins. Our research may contribute to distinguish between SRR black holes from Kerr black holes under higher-precision astronomical observations.

The Shock Cone Instabilities and Quasi-Periodic Oscillations around the Hartle–Thorne Black Hole

To explain the observed X-ray data in a black hole–accreting matter system and understand the physical mechanisms behind QPOs, we have numerically modeled the dynamical and oscillation properties of the shock cone formed around both slowly and rapidly rotating Hartle–Thorne black holes, resulting from the mechanism of Bondi–Hoyle–Lyttleton (BHL). According to the numerical simulations, an increase in the quadrupole parameter leads to a decrease in the shock cone opening angle around the black hole. A larger quadrupole parameter results in more matter falling into the black hole within the cone. The combination of the quadrupole parameter and black hole rotation causes the matter inside the cone to exhibit chaotic motion. These dynamical changes and chaotic behavior of the shock cones excite the fundamental oscillation modes. Moreover, new frequencies have been formed due to the nonlinear coupling of the fundamental modes. Conversely, we have numerically studied the behavior of cones formed around rapidly rotating Hartle–Thorne black holes and found differences and similarities to those obtained from slowly rotating cases. Finally, comparing the outcomes obtained fromHartle–Thorne gravity with the results fromKerr and Einstein–Gauss–Bonnet (EGB) gravities reveals the impact of the quadrupole parameter on the shock cone and QPOs.

Epicyclic Oscillations and Circular Orbits in Hairy Black Holes: Testing by High-Frequency Quasi-Periodic Oscillations Observed in Microquasars

Recently, Ovalle and his collaborators proposed an exact solution to Einstein’s equations. In this study, we investigate the main characteristics of the spherically symmetric spacetime determined by the hair parameter l, with a specific focus on circular orbits, particularly the innermost circular orbits (ISCOs), and the epicyclic oscillatory motion along these orbits. To assess the validity of this novel geometry, we employ the frequencies derived from the epicyclic resonance model of high-frequency quasi-periodic oscillations (HF QPOs) observed in microquasars, as well as the ISCOs. By analyzing the observed data from three selected microquasars, we establish constraints on the parameter l. Our findings suggest that this geometric framework can encompass the phenomena associated with HF QPOs and offer a partial explanation for the observed shift in the ISCOs, which is commonly attributed to the rotation of the black hole.

Optical Kerr nonlinearity of dielectric nanohole array metasurfaces with different hole shapes near the anapole state

At present, optical anapole resonances in nanostructures have attracted increasing attention due to the strong field confinement and substantially suppressed scattering. This study provides the results of three-dimensional finite-difference time-domain simulations exhibiting the possibility of the anapole state in high refractive index dielectric nanohole array metasurfaces having different profiles of the holes (square, hexagon, and octagon). Behavior of the effective optical Kerr nonlinearity of the metasurfaces in the vicinity of the anapole state is investigated. Depending on the geometry, the absolute value of the effective nonlinear Kerr coefficient of the metasurface may be up to three orders of magnitude greater than that of the unstructured film. A square transverse section of the nanohole is preferable for the optical Kerr effect in the holey metasurfaces. The effect of the random rotation of the square holes representing the metasurface irregularity on the optical nonlinearity is examined. As a result, the dielectric nanohole array metasurfaces display a concrete possibility to have the anapole state with large enhancement of the optical nonlinearity.

Phonon motion around (2+1)-dimensional acoustic black hole

We study motion of a phonon, a particle representing the quanta of the sound wave in the (2+1) spacetime of the acoustic analogous axially symmetric black hole, so-called acoustic (sonic) black hole. Similar to the real objects known as black holes in relativity theories, the phenomenon called acoustic black hole possesses the ergoregion whose area is increasing with increasing rotation of the black hole, leading to more phonons being affected by the supersonic flow. It is found that phonons in the ergoregion of an acoustic black hole behave differently than those outside of it. Specifically, we found that the phonons in the ergoregion are affected by the supersonic flow of the fluid, causing them to move in different directions than those outside the ergoregion. Moreover, we presented calculations of the deflection angle and time delay of the phonon in the field of the acoustic black hole in the weak field regime that can be useful to test the geometry of the acoustic black hole in the laboratory.

Bone powder miller optimization

Bone waste has started to emerging problem worldwide with the rise of meat consumption, thus the further processing of bone waste would help in tackling the problem as the powdered bone itself can be used for various use, from animal feed additive to cement replacement in concrete making. The built bone powder miller has performance of effective capacity of 12.03 kg/hour, 8% damaged product, and 0.35% bone powder moisture, in order to attain better performance, the miller thus optimized through the means of varying drying temperature, sieve hole size, rotation speed and testing several levels of workloads and finally testing various bone material to be powdered. Individual optimization procces was able to show best performance for optimized variables, but has no improvement to miller performance using original setting. the bone miller is expected to be able to alleviate cow bone waste problem and converting it to usable materials in form of bone powder, in turn, contributing to waste reduction while adopting zero waste concept for sustainable agricultural production.

Rotation of a Long-Lived Coronal Hole in Solar Cycle 24

Rotation of a Long-Lived Coronal Hole in Solar Cycle 24

Rotation of a Long-Lived Coronal Hole in Solar Cycle 24

This paper discusses the results of a statistical study of the rotation characteristics of a long-livedgiant coronal hole. The study is based on observation data obtained by the Atmospheric Imaging Assemblyin the Fe XII 19.3 nm line aboard the Solar Dynamics Observatory spacecraft during the period from June2015 to March 2017; this was 24 Carrington revolutions. Four stages of the development of a coronal hole areconsidered separately: formation, two phases of a developed coronal hole, and the final phase. It has beenfound that the average rotation rate at a latitude of 40° is close to the standard speed at the beginning(12.75°/day) and in the first phase of maximum development (13°/day); it is lower in the second phase ofmaximum development (11.7°/day) and at the end of its existence (12.5°/day). A slight increase in velocity atthe final stage is associated with the restructuring of the coronal hole. According to modern theories, the rotationof the solar corona reflects the rotation of the subphotospheric layers. The higher layers of the coronareflect the rotation of the deeper layers of the Sun. The results obtained in our work show that the rotationrate of a giant coronal hole in the maximum phase of its development is greater than the rotation rate of thesolar disk. Perhaps this indicates that coronal holes can be associated with deep solar layers through the configurationof the global magnetic field and that the source of coronal hole formation is deeper than the sourceof the background field.

Impact of System-F in Delivering Vascular Plugs for Aortic Side Branch Embolization During Endovascular Aneurysm Repair.

This study aimed to illustrate the utility of our original system to deliver vascular plugs into aortic side branches during endovascular aneurysm repair (EVAR). Our device, which we named "System-F," consists of a 14 Fr sheath, a 12 Fr long sheath with a side hole, a stiff guidewire as a shaft, and a parallelly-inserted delivery catheter navigated through the side hole into the aneurysm sac. Vertical motion and horizontal rotation of the side hole allow multidimensional movement of the delivery catheter within the aneurysm. This system was applied in 7 cases undergoing EVAR; 4 inferior mesenteric arteries and 14 lumbar arteries were embolized using vascular plugs. Type II endoleak (T2EL) was not observed in the follow-up survey of any case. Conclusion: The applicability of System-F for vascular plug placement in the side branches of abdominal aortic aneurysms has the potential to achieve high delivery capability and be widely applied for the prevention of T2EL. System-F has potential to change the strategies of pre-EVAR embolization.

Black hole superradiance in dynamical Chern-Simons gravity

Black hole superradiance provides a window into the dynamics of light scalar fields and their interactions close to a rotating black hole. Due to the rotation of the black hole, the amplitude of the scalar field becomes magnified, leading to a "black hole bomb" effect. Recent work has demonstrated that rotating black holes in dynamical Chern-Simons gravity possess unique structures, the "Chern-Simons caps," which may influence the behavior of matter near the black hole. Motivated by the presence of these caps, we study superradiance in dynamical Chern-Simons gravity in the context of a slowly rotating black hole. We find that additional modes are excited and contribute to the superradiance beyond what is expected for a Kerr black hole. Studying the superradiant spectrum of perturbations, we find that the Chern-Simons contributions give rise to small corrections to the angular dependence of the resulting scalar cloud. Finally, we comment on potential observable consequences and future avenues for investigation.

Carrollian motion in magnetized black hole horizons

We revisit the motion of massless particles with anyonic spin in the horizon of Kerr-Newman geometry. As recently shown, such particles can move within the horizon of the black hole due to the coupling of charges associated with a two-parametric central extension of the two-dimensional Carroll group to the magnetic field generated by the black hole---the so-called ``anyonic spin-Hall effect.'' We show that the previously computed magnetic field is not invariant under Carroll diffeomorphisms and find another result which respects these symmetries of the horizon. We also consider a more astrophysically relevant case of a (weakly charged) rotating back hole placed in a uniform magnetic field, which could, for instance, be induced by the surrounding plasma. We show that a qualitatively similar magnetic field assisted anyonic spin-Hall effect takes place, even in the absence of black hole rotation. The theoretical possibility of a motion induced by a magnetic monopole is also studied.

Polarization-switchable focal vortex beam by an Archimedean array.

Focal position control of vortex beams has tremendous applications in optical field. Herein, non-classical Archimedean arrays were proposed for optical devices with bifocal length and polarization-switchable focal length. The Archimedean arrays were constructed by rotational elliptical holes in a silver film, which were followed by two one-turned Archimedean trajectories. The elliptical holes in this Archimedean array provide the freedom of polarization control for the optical performance by their rotation status. The rotation of elliptical hole can provide additional phase to affect the shape of vortex beam (converged or diverged) under the illumination of circular polarization. The geometric phase of Archimedes trajectory will also determine the focal position of vortex beam. This Archimedean array can produce a converged vortex beam at the specific focal plane according to the handedness of the incident circular polarization and geometrical arrangement of array. The Archimedean array was also demonstrated by experiment and numerical simulation for its exotic optical performance.

Effects of the acceleration on holographic complexity

In this work, we consider a special kind of space–time called AdS accelerating black holes. This is a kind of black holes which have a stringlike singularity along polar axis attached to the black hole and it accelerates the black hole. In these kind of space–times, the growth of Einstein–Hilbert action is independent of the acceleration as found in S. Chen and Y. Pei, Int. J. Theor. Phys. 60, 917 (2021). By using a string as a probe, we found the effect of the acceleration is captured by the string probe [K. Nagasaki, arXiv:2108.05429 [hep-th]]. Here in this work, we consider the case of rotating black holes. By the probe string, we clearly describe the effect of the acceleration and its relation to the rotation of the black holes.

CFD modeling of drill cuttings transport efficiency in annular bends: Effect of hole eccentricity and rotation

Increasing the cuttings transport efficiency in deviated wells is difficult due to the rolling transport and cuttings settling on the low side of the annulus. Advancing flow rates and improving mud properties may not be applicable for proper hole cleaning because of the hydraulic and mechanical limitations. Under these situations, the major contribution to cuttings transport is provided by drill-pipe rotation for different eccentricities. This project describes the relationship between hole eccentricity and rotation during cuttings transport through annular bends. The present study focused on developing a computational fluid dynamics model by using Ansys fluent 2021 R1 to predict these parameters conveniently. Two phases were considered: liquid (water) and cuttings (sulfur solid), the Eulerian multiphase flow model was used in Fluent for the present study. The inlet boundary conditions specified the inlet velocities and volume fraction of involved phases. The stationary surfaces of the flow channels were hydrodynamically considered smooth walls and the outlets were regarded as being open to the atmosphere. The pressure gradient is used as the primary output parameter to analyze the flow. The simulated pressure losses are found to be logical at different conditions, thus showing the characteristics of the flow.

Accretion of the relativistic Vlasov gas in the equatorial plane of the Kerr black hole

We investigate stationary accretion of the collisionless Vlasov gas onto the Kerr black hole, occurring in the equatorial plane. The solution is specified by imposing asymptotic boundary conditions: at infinity the gas obeys the Maxwell-J\"uttner distribution, restricted to the equatorial plane (both in positions and momenta). In the vicinity of the black hole, the motion of the gas is governed by the spacetime geometry. We compute accretion rates of the rest-mass, the energy, and the angular momentum, as well as the particle number surface density, focusing on the dependence of these quantities on the asymptotic temperature of the gas and the black hole spin. The rest-mass and energy-accretion rates, normalized by the black hole mass and appropriate asymptotic surface densities of the gas, increase with increasing asymptotic temperature. The accretion slows down the rotation of the black hole.

Mechanical behavior of rotary friction welding joints composed of laminated veneer bamboo substrate and bamboo dowel

Rotary friction welding is a new connecting technique to produce joints by melting and re-solidification processes of substances, which has been pioneered in wooden furniture and structures due to the high interface strength. Bamboo has similar chemical components to wood and is a practical supplement to timber for applications. In this regard, the bamboo dowel was explored in this work to connect laminated veneer bamboo substrates using the rotary friction welding technique. The bond strength and shear strength of the proposed joints were experimentally evaluated by pull-out tests and single-shear tests based on the orthogonal array testing methodology. The effects of pre-drilled hole diameter, rotation rate, welding angle and substrate thickness on the mechanical behavior were investigated. The failure modes and load-carrying capacity were analyzed and discussed. Two failure modes including the pull-out failure and dowel fractured failure in pull-out tests and three failure modes including the pull-out failure, shear failure and hybrid failure of dowels in single-shear tests, were observed. It was found that the bond strength and shear strength of joints were primarily influenced by the pre-drilled hole diameter and the welding angle, respectively. The maximum bond strength of 4.40 MPa and maximum shear strength of 4.24 kN were achieved with the pre-drilled hole diameter of 8 mm and the welding angle of 45°, respectively. Furthermore, the results of scanning electron microscope observation and Fourier transform infrared spectroscopy analysis indicated that the bamboo fibers wound on the dowel surface and the relative contents of lignin increased. The research would provide the theoretical and technical basis for the application of bamboo rotary friction welding.

Ultralow-frequency broadband characteristics of stepwise radial metamaterials

A new type of stepwise radial metamaterial (SRM) with ultralow-frequency and broadband characteristics is proposed in this study. In contrast to the traditional radial metamaterial (TRM), the proposed structure is periodically arranged in a stepwise shape along the radial direction. The propagation characteristics of Lamb waves in the SRM were investigated using the finite element method. For the numerical analysis, the degeneracy between the bands of the SRM was separated, resulting in the opening of the bandgaps in the ultralow-frequency range. The total bandwidth was 75 times that of the TRM, and the wave attenuation ability was increased by more than 70%. The introduction of a stepwise array in the SRM opened up the local resonance and Bragg scattering bandgaps, and as a result, the SRM exhibited ultralow-frequency broadband characteristics. Furthermore, the influences of the structural parameters of the SRM on the bandgap characteristics were discussed. With the increase in the stepped angle, the coupling relationship between the Lamb wave mode and the local resonance was enhanced, which caused the band structure to shift to a lower frequency. In addition, the hole rotation and shape played important roles in the bandgap tuning. Finally, the experimental sample was processed based on the model, and the vibration propagation characteristics were tested to prove its ultralow-frequency broadband characteristics. The proposed shielding approach could provide a better alternative in the field of ultralow-frequency noise reduction and vibration reduction.