Journal articles: 'Black hole structure'

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Kumar, Jitendra, Shafqat Ul Islam, and Sushant G. Ghosh. "Loop Quantum Gravity motivated multihorizon rotating black holes." Journal of Cosmology and Astroparticle Physics 2022, no. 11 (November 1, 2022): 032. http://dx.doi.org/10.1088/1475-7516/2022/11/032.

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Abstract With a semiclassical polymerization in the loop quantum gravity (LQG), the interior of the Schwarzschild black holes provides a captivating single-horizon regular black hole spacetime. The shortage of rotating black hole models in loop quantum gravity (LQG) substantially restrains the progress of testing LQG from observations. Motivated by this, starting with a spherical LQG black hole as a seed metric, we construct a rotating spacetime using the revised Newman-Janis algorithm, namely, the LQG-motivated rotating black holes (LMRBH), which encompasses Kerr (l = 0) black holes as an exceptional case. We discover that for any random l > 0, unlike Kerr black hole, an extremal LMRBH refers to a black hole with angular momentum a > M. The rotating metric, in parameter space, describes (1) black holes with an event and Cauchy horizon, (2) black holes with three horizons, (3) black holes with only one horizon or (4) no horizon spacetime. We also discuss the horizon and global structure of the LMRBH spacetimes and its dependence on l/M that exhibits rich spacetime structures in the (M, a, l) parameter space.

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Ghosh, P. "The structure of black hole magnetospheres -- I. Schwarzschild black holes." Monthly Notices of the Royal Astronomical Society 315, no. 1 (June 11, 2000): 89–97. http://dx.doi.org/10.1046/j.1365-8711.2000.03410.x.

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Mahulikar, Shripad P., and Pallavi Rastogi. "Study of black hole as dissipative structure using negentropy." Canadian Journal of Physics 94, no. 10 (October 2016): 960–66. http://dx.doi.org/10.1139/cjp-2016-0388.

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The area of the event horizon of a black hole (Aeh) is so far linked only with its entropy (SBH). In this theoretical investigation, it is shown that relating Aeh only to SBH is inadequate, because Aeh is linked to the black hole’s negentropy, which encompasses its entropy. Increasing Aeh of black holes that grow now follows from the negentropy theorem (NET) and also from the well-known area theorem. The decreasing Aeh of black holes that decay follows from the converse to NET and is not a violation of the area theorem. The corollary to NET is proved for the case when two dissipative structures merge, which is the basis for the coalescence of black holes. The converse of corollary to NET explains negentropy loss due to splitting of a dissipative structure. When applied to black hole explosion (i.e., splitting into an infinite number of parts), converse of corollary to NET reduces to converse of NET. The entropy/energy ratio of the exported Hawking radiance from black holes contributes to the entropy increase of the universe. These aspects justify the consideration of black holes as thermodynamic dissipative structures.

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CHAKRABARTI, SAYAN K., KUMAR S. GUPTA, and SIDDHARTHA SEN. "UNIVERSAL NEAR-HORIZON CONFORMAL STRUCTURE AND BLACK HOLE ENTROPY." International Journal of Modern Physics A 23, no. 16n17 (July 10, 2008): 2547–61. http://dx.doi.org/10.1142/s0217751x08040482.

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It is shown that a massless scalar probe reveals a universal near-horizon conformal structure for a wide class of black holes, including the BTZ. The central charge of the corresponding Virasoro algebra contains information about the black hole. With a suitable quantization condition on the central charge, the CFT associated with the black hole in our approach is consistent with the recent observation of Witten, where the dual theory for the BTZ in the AdS/CFT framework has been identified with the construction of Frenkel, Lepowsky and Meurman. This CFT admits the Fischer–Griess monster group as its symmetry. The logarithm of the dimension of a specific representation of the monster group has been identified by Witten as the entropy of the BTZ black hole. Our algebraic approach shows that a wide class of black holes share the same near-horizon conformal structure as that for the BTZ. With a suitable quantization condition, the CFT's for all these black holes in our formalism can be identified with the FLM model, although not through the AdS/CFT correspondence. The corresponding entropy for the BTZ provides a lower bound for the entropy of this entire class of black holes.

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Nagatani, Yukinori. "Atomic Structure in Black Hole." Progress of Theoretical Physics Supplement 164 (2006): 54–67. http://dx.doi.org/10.1143/ptps.164.54.

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Deng, Gao-Ming, and Yong-Chang Huang. "Q − Φ criticality and microstructure of charged AdS black holes in f(R) gravity." International Journal of Modern Physics A 32, no. 35 (December 20, 2017): 1750204. http://dx.doi.org/10.1142/s0217751x17502049.

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The phase transition and critical behaviors of charged AdS black holes in [Formula: see text] gravity with a conformally invariant Maxwell (CIM) source and constant curvature are further investigated. As a highlight, this research is carried out by employing new state parameters [Formula: see text] and contributes to deeper understanding of the thermodynamics and phase structure of black holes. Our analyses manifest that the charged [Formula: see text]-CIM AdS black hole undergoes a first-order small–large black hole phase transition, and the critical behaviors qualitatively behave like a Van der Waals liquid–vapor system. However, differing from the case in Einstein’s gravity, phase structures of the black holes in [Formula: see text] theory exhibit an interesting dependence on gravity modification parameters. Moreover, we adopt the thermodynamic geometry to probe the black hole microscopic properties. The results show that, on the one hand, both the Ruppeiner curvature and heat capacity diverge exactly at the critical point, on the other hand, the [Formula: see text]-CIM AdS black hole possesses the property as ideal Fermi gases. Of special interest, we discover a microscopic similarity between the black holes and a Van der Waals liquid–vapor system.

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Gao, Shengyao, Zhou Tao, Yuhui Li, and Fuzhen Pang. "Application research of acoustic black hole in floating raft vibration isolation system." REVIEWS ON ADVANCED MATERIALS SCIENCE 61, no. 1 (January 1, 2022): 888–900. http://dx.doi.org/10.1515/rams-2022-0235.

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Abstract Acoustic black holes have good application prospects in the field of vibration and noise reduction. Based on engineering practice, this study proposes a systematic process method for the application of acoustic black hole structure in raft structure, which provides new ideas and references for improving the vibration isolation performance of floating raft system and reducing the level of ship vibration and noise. The influence law of each parameter on structural vibration and the recommended value range of each parameter are given, which provides support for the systematic method and process of the application of acoustic black holes in the raft structure. Then, the acoustic black hole process is applied to a floating raft system. According to the characteristics of the raft structure, an application scheme of the acoustic black hole in the raft structure is formed, and the vibration level drop of the floating raft vibration isolation system before and after the acoustic black hole is embedded, calculated, and analyzed. The changes further improve the vibration reduction and isolation performance of the raft system and effectively reduced the mechanical noise level of the ship’s cabin.

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Tang, Yang, Jiangtao Liu, Ning Liu, Fuzhen Pang, and Yu Wang. "Dynamic characteristic analysis of acoustic black hole in typical raft structure." REVIEWS ON ADVANCED MATERIALS SCIENCE 61, no. 1 (January 1, 2022): 458–76. http://dx.doi.org/10.1515/rams-2022-0038.

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Abstract As a hot content of research in recent years, acoustic black holes have bright application prospects in the field of vibration and noise reduction. In this article, based on the acoustic black hole theory, we carry out a study on the dynamic characteristics of a typical raft structure. The manuscript gives the simplified method of the acoustic black hole model, verifies the validity of the method by the structure natural frequency and vibration response, and discusses the influence of the main parameters such as acoustic black hole tip cutoff ratio and damping thickness ratio on the vibration characteristics of the raft frame structure. The better values of the parameters were applied to the raft structure on this basis, and the results showed that the peak value of some frequency points decreased by about 10 dB after the acoustic black hole was laid in the raft structure, which improved the vibration isolation performance of the raft.

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Shibata, K., S. Koide, T. Kudoh, and S. Aoki. "Jets from Black Hole Magnetospheres." Symposium - International Astronomical Union 195 (2000): 265–72. http://dx.doi.org/10.1017/s0074180900163028.

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Recent general-relativistic MHD simulations of jets ejected from black-hole magnetospheres (for both Schwarzschild and Kerr holes) have revealed that (1) strong shock waves are formed in the accretion flow inside 3rs, (2) jets show two-layered shell structure consisting of a gas-pressure driven jet and a magnetically driven jet, the former being accelerated from a high-pressure region heated by strong shocks, and (3) in the case of a Kerr hole, magnetically driven jets are produced from the ergosphere by the effect of frame dragging.

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HONG, SUNGWOOK E., DONG-HAN YEOM, and HEESEUNG ZOE. "CRITICAL REVIEWS ON HOLOGRAPHIC MEASURE OVER THE MULTIVERSE." International Journal of Modern Physics: Conference Series 01 (January 2011): 317–22. http://dx.doi.org/10.1142/s2010194511000468.

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In this talk, the holographic measure based on black hole complementarity is critically reviewed. By noticing the similarities between the causal structure of an inflationary dS space and that of a black hole, we have considered the complementarity principle between the inside and the outside of the causal horizon as an attractive way to count the inflationary multiverse. Even though the holographic measure relieves the Boltzmann brain problem and stresses the physical reality based on observations, it could be challenged by the construction of counterexamples, both on regular black holes and charged black holes, to black hole complementarity.

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Reynolds, Christopher S. "Observational Constraints on Black Hole Spin." Annual Review of Astronomy and Astrophysics 59, no. 1 (September 8, 2021): 117–54. http://dx.doi.org/10.1146/annurev-astro-112420-035022.

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The spin of a black hole is an important quantity to study, providing a window into the processes by which a black hole was born and grew. Furthermore, spin can be a potent energy source for powering relativistic jets and energetic particle acceleration. In this review, I describe the techniques currently used to detect and measure the spins of black holes. It is shown that: ▪ Two well-understood techniques, X-ray reflection spectroscopy and thermal continuum fitting, can be used to measure the spins of black holes that are accreting at moderate rates. There is a rich set of other electromagnetic techniques allowing us to extend spin measurements to lower accretion rates. ▪ Many accreting supermassive black holes are found to be rapidly spinning, although a population of more slowly spinning black holes emerges at masses above [Formula: see text] as expected from recent structure formation models. ▪ Many accreting stellar-mass black holes in X-ray binary systems are rapidly spinning and must have been born in this state. ▪ The advent of gravitational wave astronomy has enabled the detection of spin effects in merging binary black holes. Most of the premerger black holes are found to be slowly spinning, a notable exception being an object that may itself be a merger product. ▪ The stark difference in spins between the black hole X-ray binary and the binary black hole populations shows that there is a diversity of formation mechanisms. Given the array of new electromagnetic and gravitational wave capabilities currently being planned, the future of black hole spin studies is bright.

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Bronnikov, Kirill A., Júlio C. Fabris, and Denis C. Rodrigues. "On black hole structures in scalar–tensor theories of gravity." International Journal of Modern Physics D 25, no. 09 (August 2016): 1641005. http://dx.doi.org/10.1142/s0218271816410054.

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We review some properties of black hole structures appearing in gravity with a massless scalar field, with both minimal and nonminimal coupling. The main properties of the resulting cold black holes are described. The study of black holes in scalar-gravity systems is extended to [Formula: see text]-essence theories, and some examples are explicitly worked out. In these cases, even while the existence of horizons is possible, the metric regularity requirement on the horizon implies either a cold black type structure or a singular behavior of the scalar field.

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Poisson, E., and W. Israel. "Structure of the black hole nucleus." Classical and Quantum Gravity 5, no. 12 (December 1, 1988): L201—L205. http://dx.doi.org/10.1088/0264-9381/5/12/002.

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Khan, Muhammad Atif, Farhad Ali, Nahid Fatima, and Mohamed Abd El-Moneam. "Particles Dynamics in Schwarzschild like Black Hole with Time Contracting Horizon." Axioms 12, no. 1 (December 27, 2022): 34. http://dx.doi.org/10.3390/axioms12010034.

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The black holes radiate their mass and energy in the form of gravitational waves and Hawking-radiation, which lead to a decrease in the mass and energy of the black holes. During the formation of gravitational waves and Hawking radiation, the mass and energy of black holes reduce continuously with the passage of time t. For this reason the metric tensor of the black hole should depends on time t. In this work, a time-dependent term is introduced in the horizon of black hole without losing its symmetry structure by using the approximate Noether symmetry equation. The time-dependent term affects the effective potential, effective force, and all the dynamic features of the black hole. They are discussed for neutral and charged particles. Profiles of the escape velocity of colliding particles are also taken into consideration. Lyapunov exponent is used to check the stability of the orbits of the black hole. Hawking temperature, Bekenstein entropy, Komar energy, and specific energy at horizon of the black hole are discussed in this scenario.

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Pesce, Dominic W., Daniel C. M. Palumbo, Angelo Ricarte, Avery E. Broderick, Michael D. Johnson, Neil M. Nagar, Priyamvada Natarajan, and José L. Gómez. "Expectations for Horizon-Scale Supermassive Black Hole Population Studies with the ngEHT." Galaxies 10, no. 6 (December 2, 2022): 109. http://dx.doi.org/10.3390/galaxies10060109.

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We present estimates for the number of supermassive black holes (SMBHs) for which the next-generation Event Horizon Telescope (ngEHT) can identify the black hole “shadow”, along with estimates for how many black hole masses and spins the ngEHT can expect to constrain using measurements of horizon-resolved emission structure. Building on prior theoretical studies of SMBH accretion flows and analyses carried out by the Event Horizon Telescope (EHT) collaboration, we construct a simple geometric model for the polarized emission structure around a black hole, and we associate parameters of this model with the three physical quantities of interest. We generate a large number of realistic synthetic ngEHT datasets across different assumed source sizes and flux densities, and we estimate the precision with which our defined proxies for physical parameters could be measured from these datasets. Under April weather conditions and using an observing frequency of 230 GHz, we predict that a “Phase 1” ngEHT can potentially measure ∼50 black hole masses, ∼30 black hole spins, and ∼7 black hole shadows across the entire sky.

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BYTSENKO, A. A., E. ELIZALDE, and S. A. SUKHANOV. "HYPERBOLIC TOPOLOGICAL INVARIANTS AND THE BLACK HOLE GEOMETRY." International Journal of Modern Physics A 17, no. 29 (November 20, 2002): 4167–76. http://dx.doi.org/10.1142/s0217751x02013198.

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Inbarani, Hannah H., Ahmad Taher Azar, and Bagyamathi Mathiyazhagan. "Hybrid Rough Set With Black Hole Optimization-Based Feature Selection Algorithm for Protein Structure Prediction." International Journal of Sociotechnology and Knowledge Development 14, no. 1 (January 2022): 1–45. http://dx.doi.org/10.4018/ijskd.290657.

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In this paper, a new approach for hybridizing Rough Set Quick Reduct and Relative Reduct approaches with Black Hole optimization algorithm is proposed. This algorithm is inspired of black holes. A black hole is a region of spacetime where the gravitational field is so strong that nothing— not even light— that enters this region can ever escape from it. Every black hole has a mass and charge. In this Algorithm, each solution of problem is considered as a black hole and gravity force is used for global search and the electrical force is used for local search. The proposed algorithm is compared with leading algorithms such as, Rough Set Quick Reduct, Rough Set Relative Reduct, Rough Set particle swarm optimization based Quick Reduct, Rough Set based PSO Relative Reduct, Rough Set Harmony Search based Quick Reduct, and Rough Set Harmony Search based Relative Reduct.

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Saghafi, Sara, and Kourosh Nozari. "Black hole thermodynamics in Snyder phase space." International Journal of Geometric Methods in Modern Physics 14, no. 11 (October 23, 2017): 1750164. http://dx.doi.org/10.1142/s021988781750164x.

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By defining a noncommutative symplectic structure, we study thermodynamics of Schwarzschild black hole in a Snyder noncommutative phase space for the first time. Since natural cutoffs are the results of compactness of symplectic manifolds in phase space, the physics of black holes in such a space would be affected mainly by these cutoffs. In this respect, this study provides a basis for more deeper understanding of the black hole thermodynamics in a pure mathematical viewpoint.

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Afrin, Misba, and Sushant G. Ghosh. "Estimating the Cosmological Constant from Shadows of Kerr–de Sitter Black Holes." Universe 8, no. 1 (January 16, 2022): 52. http://dx.doi.org/10.3390/universe8010052.

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The Event Horizon Telescope collaboration has revealed the first direct image of a black hole, as per the shadow of a Kerr black hole of general relativity. However, other Kerr-like rotating black holes of modified gravity theories cannot be ignored, and they are essential as they offer an arena in which these theories can be tested through astrophysical observation. This motivates us to investigate asymptotically de Sitter rotating black holes wherein interpreting the cosmological constant Λ as the vacuum energy leads to a deformation in the vicinity of a black hole—new Kerr–de Sitter solution, which has a richer geometric structure than the original one. We derive an analytical formula necessary for the shadow of the new Kerr–de Sitter black holes and then visualize the shadow of black holes for various parameters for an observer at given coordinates (r0,θ0) in the domain (r0,rc) and estimate the cosmological constant Λ from its shadow observables. The shadow observables of the new Kerr–de Sitter black holes significantly deviate from the corresponding observables of the Kerr–de Sitter black hole over an appreciable range of the parameter space. Interestingly, we find a finite parameter space for (Λ, a) where the observables of the two black holes are indistinguishable.

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FERNANDO, SHARMANTHIE, and FREYDOON MANSOURI. "THE STRUCTURE OF ADS BLACK HOLES AND CHERN–SIMONS THEORY IN 2 + 1 DIMENSIONS." International Journal of Modern Physics A 14, no. 04 (February 10, 1999): 505–20. http://dx.doi.org/10.1142/s0217751x99000257.

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We study anti-de Sitter black holes in 2 + 1 dimensions in terms of Chern–Simons gauge theory of the anti-de Sitter group coupled to a source. Taking the source to be an anti-de Sitter state specified by its Casimir invariants, we show how all the relevant features of the black hole are accounted for. The requirement that the source be a unitary representation leads to a discrete tower of excited states which provide a microscopic model for the black hole.

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DeGraf, C., and D. Sijacki. "Cosmological simulations of massive black hole seeds: predictions for next-generation electromagnetic and gravitational wave observations." Monthly Notices of the Royal Astronomical Society 491, no. 4 (December 18, 2019): 4973–92. http://dx.doi.org/10.1093/mnras/stz3309.

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ABSTRACT We study how statistical properties of supermassive black holes depend on the frequency and conditions for massive seed formation in cosmological simulations of structure formation. We develop a novel method to recalculate detailed growth histories and merger trees of black holes within the framework of the Illustris simulation for several seed formation models, including a physically motivated model where black hole seeds only form in progenitor galaxies that conform to the conditions for direct collapse black hole formation. While all seed models considered here are in a broad agreement with present observational constraints on black hole populations from optical, UV, and X-ray studies, we find that they lead to widely different black hole number densities and halo occupation fractions, which are currently observationally unconstrained. In terms of future electromagnetic spectrum observations, the faint-end quasar luminosity function and the low-mass-end black hole–host galaxy scaling relations are very sensitive to the specific massive seed prescription. Specifically, the direct collapse model exhibits a seeding efficiency that decreases rapidly with cosmic time and produces much fewer black holes in low-mass galaxies, in contrast to the original Illustris simulation. We further find that the total black hole merger rate varies by more than one order of magnitude for different seed models, with the redshift evolution of the chirp mass changing as well. Supermassive black hole merger detections with LISA and International Pulsar Timing Array may hence provide the most direct means of constraining massive black hole seed formation in the early Universe.

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YOUM, DONAM. "BRANE WORLD IN A TOPOLOGICAL BLACK HOLES IN ASYMPTOTICALLY FLAT SPACE–TIME." Modern Physics Letters A 16, no. 26 (August 30, 2001): 1703–10. http://dx.doi.org/10.1142/s0217732301005035.

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We study static brane configurations in the bulk background of the topological black holes in asymptotically flat space–time and find that such configurations are possible even for flat black hole horizon, unlike the AdS black hole case. We construct the brane world model with an orbifold structure S1/Z2 in such bulk background and study massless bulk scalar field.

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Narzilloev, Bakhtiyor, and Bobomurat Ahmedov. "Observational and Energetic Properties of Astrophysical and Galactic Black Holes." Symmetry 15, no. 2 (January 20, 2023): 293. http://dx.doi.org/10.3390/sym15020293.

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The work reviews the investigation of electromagnetic, optical, and energetic properties of astrophysical and galactic black holes and surrounding matter. The astrophysical applications of the theoretical models of black hole environment to the description of various observed phenomena, such as cosmic rays of the ultra-high-energy, black hole shadow, gravitational lensing, quasinormal modes, jets showing relativistic effects such as the Doppler beaming, thermal radiation from the accretion discs, quasiperiodic oscillations are discussed. It has been demonstrated that the observational data strongly depends on the structure and evolution of the accretion disk surrounding the central black hole. It has been shown that the simulated images of supermassive black holes obtained are in agreement with the observational images obtained by event horizon telescope collaboration. High energetic activity from supermassive black holes due to the magnetic Penrose process discussed in the work is in agreement with the highly energetic cosmic rays observed. The astronomical observation of black holes provides rich fundamental physics laboratories for experimental tests and verification of various models of black hole accretion and different theories of gravity in the regime of strong gravity.

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NIELSEN, ALEX B., and DONG-HAN YEOM. "SPHERICALLY SYMMETRIC TRAPPING HORIZONS, THE MISNER–SHARP MASS AND BLACK HOLE EVAPORATION." International Journal of Modern Physics A 24, no. 28n29 (November 20, 2009): 5261–85. http://dx.doi.org/10.1142/s0217751x09045984.

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We discuss some of the issues relating to information loss and black hole thermodynamics in the light of recent work on local black hole horizons. Understood in terms of pure states evolving into mixed states, the possibility of information loss in black holes is closely related to the global causal structure of space–time, as is the existence of event horizons. However, black holes need not be defined by event horizons, and in fact we argue that in order to have a fully unitary evolution for black holes, they should be defined in terms of something else, such as a trapping horizon. The Misner–Sharp mass in spherical symmetry shows very simply how trapping horizons can give rise to black hole thermodynamics, Hawking radiation and singularities. We show how the Misner–Sharp mass can also be used to give insights into the process of collapse and evaporation of locally defined black holes.

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Bozza, Valerio. "Gravitational lensing by black holes and their alternatives." International Journal of Modern Physics D 26, no. 05 (April 2017): 1741013. http://dx.doi.org/10.1142/s0218271817410139.

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Black holes have the ability to generate infinite number of images of any given source. These relativistic images are formed by light rays winding around the black hole several times. The phenomenology associated with these images is very rich, since these features are very sensitive to the metric structure of the black hole. Here, we review some aspects of gravitational lensing by black holes and consider some fundamental aspects related to alternative solutions, which do not reproduce Schwarzschild in the asymptotic limit and are supported by exotic matter.

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Afrin, Misba, Rahul Kumar, and Sushant G. Ghosh. "Parameter estimation of hairy Kerr black holes from its shadow and constraints from M87*." Monthly Notices of the Royal Astronomical Society 504, no. 4 (May 4, 2021): 5927–40. http://dx.doi.org/10.1093/mnras/stab1260.

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ABSTRACT The recently obtained hairy Kerr black holes, due to additional sources or surrounding fluid, like dark matter, with conserved energy-momentum tensor, have a deviation α and primary hair l0, apart from rotation parameter a and mass M. In the wake of the Event Horizon Telescope (EHT) observations of the supermassive black hole M87*, a recent surge in interest in black hole shadows suggests comparing the black holes in general relativity and modified theories of gravity to assess these models’ differences. Motivated by this, we take on an extensive study of the rotating hairy Kerr black holes, which encompasses, in particular cases, the Kerr black hole (α = 0). We investigate ergosphere and shadows of the black holes to infer that their size and shape are affected due to the l0 and are found to harbour a richer chaotic structure. In particular, the hairy Kerr black holes possess smaller size but more distorted shadows when compared with Kerr black holes. We also estimate the parameters l0 and a associated with hairy Kerr black holes using the shadow observables. The inferred circularity deviation ΔC ≤ 0.1 for the M87* black hole is satisfied, whereas shadow angular diameter θd = 42 ± 3μas, within 1σ region, for a given choice of α, places bounds on the parameters a and l0. Interestingly, the shadow axial ratio obeying 1 < Dx ≲ 4/3 is in agreement with the EHT results and thus eventuates in the hairy Kerr black holes being suitable candidates for astrophysical black holes.

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O'Connor, Evan, Luc Dessart, and Christian D. Ott. "Black-Hole Formation in Potential γ-Ray Burst Progenitors." Proceedings of the International Astronomical Union 7, S279 (April 2011): 373–74. http://dx.doi.org/10.1017/s1743921312013415.

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AbstractWe present the results of a study by Dessart et al. (2012), where we performed stellar collapse simulations of proposed long-duration γ-ray burst (LGRB) progenitor models and assessed the prospects for black hole formation. We find that many of the proposed LGRB candidates in Woosley & Heger (2006) have core structures similar to garden-variety core-collapse supernova progenitors and thus are not expected to form black holes, which is a key ingredient of the collapsar model of LGRBs. The small fraction of proposed progenitors that are compact enough to form black holes have fast rotating iron cores, making them prone to a magneto-rotational explosion and the formation of a proto-magnetar rather than a black hole. This leads us to our take-home message, that one must consider the iron-core structure (eg. ρ(r), Ω(r)) of evolved massive stars before making assumptions on the central engine of LGRBs.

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Deng, Gao-Ming, Jinbo Fan, and Xinfei Li. "Effects of global monopole on critical behaviors and microstructure of charged AdS black holes." Modern Physics Letters A 36, no. 26 (August 30, 2021): 2150191. http://dx.doi.org/10.1142/s0217732321501911.

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As an intriguing topological defect, global monopole’s influence on behaviors of black holes has always been anticipated but still remains obscure. Analyzing the thermodynamics of charged Anti-de Sitter (AdS) black hole incorporating a global monopole manifests that the black hole undergoes a Van der Waals-like first-order phase transition near the critical point. This paper concentrates on further investigating the transition, aiming at clarifying how the global monopole affects the criticality and microstructure of the charged AdS black holes. As a highlight, this research is implemented by employing new state parameters other than (T, P, V) description and contributes to deeper understanding the rich critical phenomena and phase structure of black holes.

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Qin, Y., T. Fragos, G. Meynet, J. Andrews, M. Sørensen, and H. F. Song. "The spin of the second-born black hole in coalescing binary black holes." Astronomy & Astrophysics 616 (August 2018): A28. http://dx.doi.org/10.1051/0004-6361/201832839.

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Context. Various binary black hole formation channels have been proposed since the first gravitational event GW150914 was discovered by the Advanced Laser Interferometer Gravitational-Wave Observatory (AdLIGO). The immediate progenitor of the binary black hole is a close binary system composed of a black hole and a helium star, which can be the outcome of the classical isolated binary evolution through the common envelope, or alternatively of the massive close evolution through chemically homogeneous channel. Aims. We study the spin angular momentum evolution of the helium star in order to constrain the spin of the second-born black hole. This work focuses on the common envelope formation channel, however, some of our conclusions are also relevant for the chemically homogeneous evolution channel. Methods. We perform detailed stellar structure and binary evolution calculations that take into account, mass-loss, internal differential rotation, and tidal interactions between the helium star and the black hole companion, where we also calculate the strength of the tidal interactions from first principles based on the structure of the helium stars. We systematically explore the parameter space of initial binary properties, including initial black hole and helium star masses, initial rotation of the helium star as well as metallicity. Results. We argue that the natal spin of the first-born black hole through the common envelope scenario is negligible (≲0.1), and therefore the second-born black hole’s spin dominates the measured effective spin, χeff, from gravitational wave events of double black hole mergers. We find that tides can be only important when orbital periods are shorter than 2 days. Upon core collapse, the helium star produces a black hole (the second-born black hole in the system) with a spin that can span the entire range from zero to maximally spinning. We show that the bimodal distribution of the spin of the second-born black hole obtained in recent papers is mainly due to oversimplifying assumptions. We find an anti-correlation between the merging timescale of the two black holes, Tmerger, and the effective spin χeff. Finally, we provide new prescriptions for the tidal coefficient E2 for both H-rich and the He-rich stars. Conclusions. To understand the spin of the second-born black hole, careful treatment of both tides and stellar winds is needed. We predict that, with future improvements to AdLIGO’s sensitivity, the sample of merging binary black hole systems will show an overdensity of sources with positive but small χeff originating from lower-mass black hole mergers born at low redshift.

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KAWAI, HIKARU, YOSHINORI MATSUO, and YUKI YOKOKURA. "SPACETIME STRUCTURE OF THE BLACK HOLE EVAPORATION." International Journal of Modern Physics: Conference Series 21 (January 2013): 167–68. http://dx.doi.org/10.1142/s2010194513009641.

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We study a self-consistent solution of the semi-classical Einstein equation including the back reaction from the Hawking radiation. Our geometry is constructed by connecting flat space and the outgoing Vaidya metric at the locus of the shock wave. In order to prove that this is the self-consistent solution, we first show that the Weyl anomaly is canceled if we take the effects of the fluctuations of the metric into account. We further demonstrate that the Hawking radiation occurs even if the geometry has no horizon. Then, the energy-momentum tensor is found to be consistent with the semi-classical Einstein equation. Since our geometry has neither horizon nor singularity, all matters inside the black hole finally come back to infinity. Therefore, no information is lost by the black hole evaporation. Furthermore, we take into account the gray-body factor. We construct a stationary solution for a black hole in the heat bath and estimate the entropy. The entropy-area law is reproduced by the volume integration of the entropy density over the inside of the horizon, and the black hole can be treated as an ordinary thermodynamic object.

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31

Poon, M. Y., and D. Merritt. "Orbital Structure of Triaxial Black Hole Nuclei." Astrophysical Journal 549, no. 1 (March 2001): 192–204. http://dx.doi.org/10.1086/319060.

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Khlopov, M. Yu, S. G. Rubin, and A. S. Sakharov. "Primordial structure of massive black hole clusters." Astroparticle Physics 23, no. 2 (March 2005): 265–77. http://dx.doi.org/10.1016/j.astropartphys.2004.12.002.

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Richstone, Douglas. "11.1. Black holes and galaxy centers." Symposium - International Astronomical Union 184 (1998): 451–58. http://dx.doi.org/10.1017/s0074180900085557.

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The study of supermassive galactic black holes (BH) has moved beyond discovery to maturity. The are now ∼ 15 reliable detections. The mass of a central black hole apparently correlates with the mass of the hot component of its galactic host. It may be that every normal galaxy has a supermassive black hole carrying about 10−3 of its bulge mass, with important consequences for the structure and evolution of the core of the galaxy. The most recent major review is by Kormendy & Richstone (1995, KR).

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34

Al-Modlej, Abeer, Salwa Alsaleh, Hassan Alshal, and Ahmed Farag Ali. "Proton decay and the quantum structure of space–time." Canadian Journal of Physics 97, no. 12 (December 2019): 1317–22. http://dx.doi.org/10.1139/cjp-2018-0423.

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Virtual black holes in noncommutative space–time are investigated using coordinate coherent state formalism such that the event horizon of a black hole is manipulated by smearing it with a Gaussian of width [Formula: see text], where θ is the noncommutativity parameter. Proton lifetime, the main associated phenomenology of the noncommutative virtual black holes, has been studied, first in four-dimensional space–time and then generalized to D dimensions. The lifetime depends on θ and the number of space–time dimensions such that it emphasizes on the measurement of proton lifetime as a potential probe for the microstructure of space–time.

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Dexter, J. "Event horizon scale emission models for Sagittarius A*." Proceedings of the International Astronomical Union 9, S303 (October 2013): 298–302. http://dx.doi.org/10.1017/s1743921314000775.

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AbstractVery long baseline interferometry observations at millimeter wavelengths have detected source structure in Sgr A* on event horizon scales. Near-infrared interferometry will achieve similar resolution in the next few years. These experiments provide an unprecedented opportunity to explore strong gravity around black holes, but interpreting the data requires physical modeling. I discuss the calculation of images, spectra, and light curves from relativistic MHD simulations of black hole accretion. The models provide an excellent description of current observations, and predict that we may be on the verge of detecting a black hole shadow, which would constitute the first direct evidence for the existence of black holes.

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GE, XIAN-HUI, and YOU-GEN SHEN. "RELATING QUANTUM INFORMATION TO CHARGED BLACK HOLES." International Journal of Modern Physics D 14, no. 08 (August 2005): 1321–31. http://dx.doi.org/10.1142/s0218271805007073.

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Quantum non-cloning theorem and a thought experiment are discussed for charged black holes whose global structure exhibits an event and a Cauchy horizon. We take Reissner–Norström black holes and two-dimensional dilaton black holes as concrete examples. The results show that the quantum non-cloning theorem and the black hole complementarity are far from consistent inside the inner horizon. The relevance of this work to non-local measurements is briefly discussed.

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Donmez, Orhan, Fatih Dogan, and Tuba Sahin. "Study of Asymptotic Velocity in the Bondi–Hoyle Accretion Flows in the Domain of Kerr and 4-D Einstein–Gauss–Bonnet Gravities." Universe 8, no. 9 (September 2, 2022): 458. http://dx.doi.org/10.3390/universe8090458.

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Understanding the physical structures of the accreted matter very close to a black hole in quasars and active galactic nucleus (AGN) is an important milestone to constrain the activities occurring in their centers. In this paper, we numerically investigate the effects of the asymptotic velocities on the physical structures of the accretion disk around the Kerr and Einstein–Gauss–Bonnet (EGB) rapidly rotating black holes. The Bondi–Hoyle accretion is considered with a falling gas towards the black hole in an upstream region of the computational domain. Shock cones are naturally formed in the downstream part of the flow around both black holes. The structure of the cones and the amount of the accreted matter depend on asymptotic velocity V∞ (Mach number) and the types of the gravities (Kerr or EGB). Increasing the Mach number of the in-flowing matter in the supersonic region reduces the shock opening angle and the accretion rates, because of the gas rapidly falling towards the black hole. The EGB gravity leads to an increase in the shock opening angle of the shock cones while the mass-accretion rates dM/dt decrease in EGB gravity with a Gauss–Bonnet (GB) coupling constant α. It is also confirmed that accretion rates and drag forces are significantly altered in the EGB gravity. Our numerical simulation results could be used in identifying the accretion mechanism and physical properties of the accretion disk and black hole in the observed X-rays such as NGC 1313 X-1 and 1313 X-2 and MAXI J1803-298.

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Liu, Z., Y. Zhou, and A. Golyanin. "Simulation Study on the Blocking Effect and Vibration Reduction Characteristics of Acoustic Black Hole in Thin Plate." Bulletin of Science and Practice 6, no. 4 (April 15, 2020): 223–31. http://dx.doi.org/10.33619/2414-2948/53/26.

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Recently, more and more scholars have devoted themselves to researching new methods of vibration reduction and noise reduction by manipulating the elastic waves in the structure to achieve the purpose of vibration reduction and noise reduction. To this end, a new type of ‘acoustic black hole’ structure is proposed, which reduces structural vibration while avoiding problems such as mass increase. In this paper, the vibration damping performance of the structure is mainly calculated by finite element software, and the energy concentration effect of the thin plate containing the acoustic black hole is verified by finite element analysis. A thin plate structure with four acoustic black holes is proposed. The calculation shows that the structure has obvious vibration reduction effect, and the vibration reduction effect can reach more than 20dB at high frequency.

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Shaymatov, Sanjar, Bobomurat Ahmedov, Zdeněk Stuchlík, and Ahmadjon Abdujabbarov. "Effect of an external magnetic field on particle acceleration by a rotating black hole surrounded with quintessential energy." International Journal of Modern Physics D 27, no. 08 (May 30, 2018): 1850088. http://dx.doi.org/10.1142/s0218271818500888.

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We investigate particle motion and collisions in the vicinity of rotating black holes immersed in combined cosmological quintessential scalar field and external magnetic field. The quintessential dark-energy field governing the spacetime structure is characterized by the quintessential state parameter [Formula: see text] characterizing its equation of state, and the quintessential field-intensity parameter [Formula: see text] determining the static radius where the black hole attraction is just balanced by the quintessential repulsion. The magnetic field is assumed to be test field that is uniform close to the static radius, where the spacetime is nearly flat, being characterized by strength [Formula: see text] there. Deformations of the test magnetic field in vicinity of the black hole, caused by the Ricci non-flat spacetime structure are determined. General expression of the center-of-mass energy of the colliding charged or uncharged particles near the black hole is given and discussed in several special cases. In the case of nonrotating black holes, we discuss collisions of two particles freely falling from vicinity of the static radius, or one such a particle colliding with charged particle revolving at the innermost stable circular orbit. In the case of rotating black holes, we discuss briefly particles falling in the equatorial plane and colliding in close vicinity of the black hole horizon, concentrating attention to the interplay of the effects of the quintessential field and the external magnetic field. We demonstrate that the ultra-high center-of-mass energy can be obtained for black holes placed in an external magnetic field for an infinitesimally small quintessential field-intensity parameter [Formula: see text]; the center-of-mass energy decreases if the quintessential field-intensity parameter [Formula: see text] increases.

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40

Król, Jerzy, and Torsten Asselmeyer-Maluga. "Categorical Smoothness of 4-Manifolds from Quantum Symmetries and the Information Loss Paradox." Entropy 24, no. 3 (March 11, 2022): 391. http://dx.doi.org/10.3390/e24030391.

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In this paper, we focus on some aspects of the relation of spacetime and quantum mechanics and the study counterparts (in Set) of the categorical local symmetries of smooth 4-manifolds. In the set-theoretic limit, there emerge some exotic smoothness structures on R4 (hence the Riemannian nonvanishing curvature), which fit well with the quantum mechanical lattice of projections on infinite-dimensional Hilbert spaces. The method we follow is formalization localized on the open covers of the spacetime manifold. We discuss our findings in the context of the information paradox assigned to evaporating black holes. A black hole can evaporate entirely, but the smoothness structure of spacetime will be altered and, in this way, the missing information about the initial states of matter forming the black hole will be encoded. Thus, the possible global geometric remnant of black holes in spacetime is recognized as exotic 4-smoothness. The full-fledged verification of this proposal will presumably be possible within the scope of future quantum gravity theory research.

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Quevedo, Hernando, María N. Quevedo, and Alberto Sánchez. "Geometrothermodynamics of black hole binary systems." International Journal of Modern Physics D 29, no. 08 (May 20, 2020): 2050053. http://dx.doi.org/10.1142/s0218271820500534.

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We study a stationary and axisymmetric binary system composed of two identical Kerr black holes, whose physical parameters satisfy the Smarr thermodynamic formula. Then, we use the formalism of geometrothermodynamics to show that the spatial distance between the black holes must be considered as a thermodynamic variable. We investigate the main thermodynamic properties of the system by using the contact structure of the phase-space, which generates the first law of thermodynamics and the equilibrium conditions. The phase transition structure of the system is investigated through the curvature singularities of the equilibrium space. It is shown that the thermodynamic and stability properties and the phase transition structure of the binary system strongly depend on the distance between the black holes.

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Duggal, K. L. "Evolving Null Horizons Near an Isolated Black Hole." Applied Physics Research 8, no. 3 (May 1, 2016): 90. http://dx.doi.org/10.5539/apr.v8n3p90.

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Totally geodesic null hypersurfaces have been widely used as models of time-independent event and isolated black hole horizons. However, in reality black hole being surrounded by a local mass distribution there is significant difference in the structure of the surrounding region of isolated black holes. In this paper, we use metric conformal symmetry which provides a class of a family of totally umbilical null hypersurfaces (Theorem 4), supported by a physical model and an example of time-dependent evolving null horizons (see Definition 6) conformally related to <br />an isolated black hole. We establish an interrelation between the spacelike dynamical horizons (see Definition 7), isolated and evolving null horizons. Finally we propose further study on null geometry and physics of the surface closer to an isolated horizon.

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YEOM, DONG-HAN, and HEESEUNG ZOE. "SEMICLASSICAL BLACK HOLES WITH LARGE N RESCALING AND INFORMATION LOSS PROBLEM." International Journal of Modern Physics A 26, no. 19 (July 30, 2011): 3287–314. http://dx.doi.org/10.1142/s0217751x11053924.

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We consider semiclassical black holes and related rescalings with N massless fields. For a given semiclassical solution of an N = 1 universe, we can find other solution of a large N universe by the rescaling. After the rescaling, any curvature quantity takes a sufficiently small value without changing its causal structure. Via the rescaling, we argue that black hole complementarity for semiclassical black holes cannot provide a fundamental resolution of the information loss problem, and the violation of black hole complementarity requires sufficiently reasonable amounts of N. Such N might be realized from some string inspired models. Finally, we claim that any fundamental resolution of the information loss problem should resolve the problem of the singularity.

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Huang, Yang, and Hongsheng Zhang. "Dirac Clouds around Dilatonic Black Holes." Research 2022 (March 4, 2022): 1–8. http://dx.doi.org/10.34133/2022/9823274.

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Dirac cloud is in absence in general relativity since the superradiance mechanism fails to work for Dirac fields. For the first time, we find a novel mechanism to support Dirac clouds, which is independent on superradiance mechanism. We study quasibound states of Dirac particles around a charged spherical black hole in dilatonic gravity. We find that the quasibound states become real bound states when the central black hole becomes extremal. We make an intensive study of the energy spectrum of the stationary clouds for different fine structure constant μM and reveal the existence condition of these clouds. Our result strongly implies that extreme dilatonic black holes behave as elementary particles.

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Hubeny, Ivan, and Dayal T. Wickramasinghe. "X-Ray Heated Accretion Discs Around Stellar Mass Black Holes." International Astronomical Union Colloquium 194 (2004): 200–201. http://dx.doi.org/10.1017/s0252921100152479.

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We investigate the effects of irradiation on the vertical structure of accretion discs around black holes and its impact on the emergent energy distribution. Models are presented for a 10 Solar mass black hole in a low mass X-ray binary assuming a black body spectrum for the incident radiation. We show that for a disc annulus at a given radius, the spectra become increasingly distorted as the incident flux increases relative to the viscously generated heating flux in the disc. Significant effects are apparent for rings even at distances of ~ 10,000 Schwarzschild radii from the black hole for realistic dilution factors.

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Zou, De-Cheng, Ming Zhang, and Ruihong Yue. "Phase Structure and Quasinormal Modes of AdS Black Holes in Rastall Theory." Advances in High Energy Physics 2020 (January 22, 2020): 1–9. http://dx.doi.org/10.1155/2020/8039183.

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We discuss the P−V criticality and phase transition in the extended phase space of anti-de Sitter(AdS) black holes in four-dimensional Rastall theory and recover the Van der Waals (VdW) analogy of small/large black hole (SBH/LBH) phase transition when the parameters ωs and ψ satisfy some certain conditions. Later, we further explore the quasinormal modes (QNMs) of massless scalar perturbations to probe the SBH/LBH phase transition. It is found that it can be detected near the critical point, where the slopes of the QNM frequencies change drastically in small and large black holes.

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Komossa, S., J. G. Baker, and F. K. Liu. "Growth of Supermassive Black Holes, Galaxy Mergers and Supermassive Binary Black Holes." Proceedings of the International Astronomical Union 11, A29B (August 2015): 292–98. http://dx.doi.org/10.1017/s1743921316005378.

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AbstractThe study of galaxy mergers and supermassive binary black holes (SMBBHs) is central to our understanding of the galaxy and black hole assembly and (co-)evolution at the epoch of structure formation and throughout cosmic history. Galaxy mergers are the sites of major accretion episodes, they power quasars, grow supermassive black holes (SMBHs), and drive SMBH-host scaling relations. The coalescing SMBBHs at their centers are the loudest sources of gravitational waves (GWs) in the Universe, and the subsequent GW recoil has a variety of potential astrophysical implications which are still under exploration. Future GW astronomy will open a completely new window on structure formation and galaxy mergers, including the direct detection of coalescing SMBBHs, high-precision measurements of their masses and spins, and constraints on BH formation and evolution in the high-redshift Universe.

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Nomura, Yasunori. "From the black hole conundrum to the structure of quantum gravity." Modern Physics Letters A 36, no. 08 (January 27, 2021): 2130007. http://dx.doi.org/10.1142/s021773232130007x.

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We portray the structure of quantum gravity emerging from recent progress in understanding the quantum mechanics of an evaporating black hole. Quantum gravity admits two different descriptions, based on Euclidean gravitational path integral and a unitarily evolving holographic quantum system, which appear to present vastly different pictures under the existence of a black hole. Nevertheless, these two descriptions are physically equivalent. Various issues of black hole physics — including the existence of the interior, unitarity of the evolution, the puzzle of too large interior volume, and the ensemble nature seen in certain calculations — are addressed very differently in the two descriptions, still leading to the same physical conclusions. The perspective of quantum gravity developed here is expected to have broader implications beyond black hole physics, especially for the cosmology of the eternally inflating multiverse.

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Cavalcanti, Rogerio Teixeira, Kelvin dos Santos Alves, and Julio Marny Hoff da Silva. "Near-Horizon Thermodynamics of Hairy Black Holes from Gravitational Decoupling." Universe 8, no. 7 (July 1, 2022): 363. http://dx.doi.org/10.3390/universe8070363.

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The horizon structure and thermodynamics of hairy spherically symmetric black holes generated by the gravitational decoupling method are carefully investigated. The temperature and heat capacity of the black hole is determined, as well as how the hairy parameters affect the thermodynamics. This allows for an analysis of thermal stability and the possible existence of a remanent black hole. We also calculate the Hawking radiation corrected by the generalized uncertainty principle. We consider the emission of fermions and apply the tunneling method to the generalized Dirac equation. This shows that, despite the horizon location being the same as the Schwarzschild one for a suitable choice of parameters, the physical phenomena that occur near the horizon of both black holes are qualitatively different.

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DEHGHANI, M. H., N. BOSTANI, and R. POURHASAN. "TOPOLOGICAL BLACK HOLES OF GAUSS–BONNET–YANG–MILLS GRAVITY." International Journal of Modern Physics D 19, no. 07 (July 2010): 1107–17. http://dx.doi.org/10.1142/s0218271810017196.

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We present the asymptotically AdS solutions of Gauss–Bonnet gravity with hyperbolic horizon in the presence of a non-Abelian Yang–Mills field with the gauge semisimple group So(n(n-1)/2-1, 1). We investigate the properties of these solutions and find that the non-negative mass solutions in six and higher dimensions are real everywhere with spacelike singularities. They present black holes with one horizon and have the same causal structure as the Schwarzschild space–time. The solutions in five dimensions or the solutions in higher dimensions with negative mass are not real everywhere. In these cases, one needs a transformation to make the solutions real. These solutions may present a naked singularity, an extreme black hole, a black hole with two horizons, or a black hole with one horizon.

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Journal articles on the topic 'Black hole structure'

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