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Universe
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Black Hole Physics and Astrophysics
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Black Hole Physics and Astrophysics

A special issue of Universe (ISSN 2218-1997).

Deadline for manuscript submissions: closed (29 February 2020) | Viewed by 20470

Special Issue Editor

Prof. Dr. Vyacheslav Ivanovich Dokuchaev

E-Mail Website
Guest Editor
Institute for Nuclear Research of the Russian Academy of Sciences, Moscow 117312, Russia
Interests: black holes; cosmology; theory of gravity; physics of the early universe

Special Issue Information

Dear Colleagues,

Nowadays the technological achievements in astrophysical observations earnestly demonstrate that black holes are the most important objects in the universe. Comprehensive observational and theoretical investigations are urgently requested for better understanding of black hole physics, as the outside and also inside of the black hole event horizon.

Reviews and papers with fresh data and ideas are especially welcome.

Prof. Dr. Vyacheslav Ivanovich Dokuchaev
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Universe is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Black holes
  • Primordial black holes
  • Cosmological black holes
  • Black hole interiors
  • Dark energy around black holes
  • Dark matter around black holes
  • Physics of the early universe
  • Theory of gravity
  • Einstein gravity
  • Black holes in modified gravity
  • Spacetime singularities
  • Astroparticle physics
  • Relativistic accretion
  • Gravitational waves

Published Papers (7 papers)

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Research

11 pages, 307 KiB  
Article
Entropy and Energy of Static Spherically Symmetric Black Hole in f(R) Theory
by Yaoguang Zheng and Rong-Jia Yang
Universe 2020, 6(3), 47; https://doi.org/10.3390/universe6030047 - 20 Mar 2020
Cited by 4 | Viewed by 1839
Abstract
We consider the new horizon first law in f ( R ) theory. We derive the general formulas to computed the entropy and energy for static spherically symmetric black hole. For applications, some nontrivial solutions in some popular f ( R ) theories [...] Read more.
We consider the new horizon first law in f ( R ) theory. We derive the general formulas to computed the entropy and energy for static spherically symmetric black hole. For applications, some nontrivial solutions in some popular f ( R ) theories are investigated, the entropies and the energies of static spherically symmetric black holes in these models are first calculated. Full article
(This article belongs to the Special Issue Black Hole Physics and Astrophysics)
13 pages, 1278 KiB  
Article
Investigation of Infrasound Background Noise at Mátra Gravitational and Geophysical Laboratory (MGGL)
by Edit Fenyvesi, József Molnár and Sándor Czellár
Universe 2020, 6(1), 10; https://doi.org/10.3390/universe6010010 - 03 Jan 2020
Cited by 2 | Viewed by 2383
Abstract
Infrasound and seismic waves are supposed to be the main contributors to the gravity-gradient noise (Newtonian noise) of the third-generation subterranean gravitational wave detectors. This noise will limit the sensitivity of the instrument at frequencies below 20 Hz. Investigation of its origin and [...] Read more.
Infrasound and seismic waves are supposed to be the main contributors to the gravity-gradient noise (Newtonian noise) of the third-generation subterranean gravitational wave detectors. This noise will limit the sensitivity of the instrument at frequencies below 20 Hz. Investigation of its origin and the possible methods of mitigation have top priority during the designing period of the detectors. Therefore, long-term site characterizing measurements are needed at several subterranean sites. However, at some sites, mining activities can occur. These activities can cause sudden changes (transients) in the measured signal, and increase the continuous background noise, too. We have developed an algorithm based on discrete Haar transform to find these transients in the infrasound signal. We found that eliminating the transients decreases the variation of the noise spectra, and therefore results a more accurate characterization of the continuous background noise. We carried out experiments for controlling the continuous noise. Machines operating at the mine were turned on and off systematically in order to see their effect on the noise spectra. These experiments showed that the main contributor of the continuous noise is the ventilation system of the mine. We also estimated the contribution of infrasound Newtonian noise at MGGL to the strain noise of a subterranean GW detector similar to Einstein Telescope. Full article
(This article belongs to the Special Issue Black Hole Physics and Astrophysics)
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21 pages, 4264 KiB  
Article
Decline of the Current Quadrupole Moment during the Merger Phase of Binary Black Hole Coalescence
by Fan Zhang
Universe 2020, 6(1), 3; https://doi.org/10.3390/universe6010003 - 25 Dec 2019
Cited by 2 | Viewed by 2820
Abstract
Utilizing the tools of tendex and vortex, we study the highly dynamic plunge and merger phases of several π -symmetric binary black hole coalescences. In particular, we observe a decline of the strength of the current quadrupole moment compared to that of the [...] Read more.
Utilizing the tools of tendex and vortex, we study the highly dynamic plunge and merger phases of several π -symmetric binary black hole coalescences. In particular, we observe a decline of the strength of the current quadrupole moment compared to that of the mass quadrupole moment during the merger phase, contrary to a naive estimate according to the dependence of these moments on the separation between the black holes. We further show that this decline of the current quadrupole moment is achieved through the remnants of the two individual spins becoming nearly aligned or anti-aligned with the total angular momentum. We also speculate on the ability to achieve a consistency between the electric and magnetic parity quasinormal modes. Full article
(This article belongs to the Special Issue Black Hole Physics and Astrophysics)
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18 pages, 2534 KiB  
Article
Static State of a Black Hole Supported by Dark Matter
by Boris E. Meierovich
Universe 2019, 5(9), 198; https://doi.org/10.3390/universe5090198 - 13 Sep 2019
Cited by 9 | Viewed by 2781
Abstract
The possibility of an equilibrium state of a gravitating scalar field (describing ordinary matter) inside a black hole, compressed to the state of boson condensate, in balance with a longitudinal vector field (describing dark matter) from the outside, is considered. Analytical analysis, confirmed [...] Read more.
The possibility of an equilibrium state of a gravitating scalar field (describing ordinary matter) inside a black hole, compressed to the state of boson condensate, in balance with a longitudinal vector field (describing dark matter) from the outside, is considered. Analytical analysis, confirmed numerically, shows that there are regular static solutions to the Einstein equations with no limitation on the mass of a black hole. The metric tensor component grr(r) changes sign twice. The behavior of the gravitational field and material fields in the vicinity of these two Schwarzschild radii were studied in detail. The equality of the energy–momentum tensors of the scalar and longitudinal vector fields at the interface supports the phase equilibrium of a black hole and dark matter. Considering the gravitating scalar field as an example, a possible internal structure of a black hole and its influence on the dark matter at the periphery of a galaxy are clarified. In particular, the speed on the plateau of a galaxy rotation curve as a function of a black hole’s mass is determined. Full article
(This article belongs to the Special Issue Black Hole Physics and Astrophysics)
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19 pages, 2719 KiB  
Article
Hot Accretion Flow in Two-Dimensional Spherical Coordinates: Considering Pressure Anisotropy and Magnetic Field
by Hui-Hong Deng and De-Fu Bu
Universe 2019, 5(9), 197; https://doi.org/10.3390/universe5090197 - 12 Sep 2019
Cited by 2 | Viewed by 2420
Abstract
For systems with extremely low accretion rate, such as Galactic Center Sgr A* and M87 galaxy, the ion collisional mean free path can be considerably larger than its Larmor radius. In this case, the gas pressure is anisotropic to magnetic field lines. In [...] Read more.
For systems with extremely low accretion rate, such as Galactic Center Sgr A* and M87 galaxy, the ion collisional mean free path can be considerably larger than its Larmor radius. In this case, the gas pressure is anisotropic to magnetic field lines. In this paper, we pay attention to how the properties of outflow change with the strength of anisotropic pressure and the magnetic field. We use an anisotropic viscosity to model the anisotropic pressure. We solve the two-dimensional magnetohydrodynamic (MHD) equations in spherical coordinates and assume that the accretion flow is radially self-similar. We find that the work done by anisotropic pressure can heat the accretion flow. The gas temperature is heightened when anisotropic stress is included. The outflow velocity increases with the enhancement of strength of the anisotropic force. The Bernoulli parameter does not change much when anisotropic pressure is involved. However, we find that the energy flux of outflow can be increased by a factor of 20 in the presence of anisotropic stress. We find strong wind (the mass outflow is about 70% of the mass inflow rate) is formed when a relatively strong magnetic field is present. Outflows from an active galactic nucleus can interact with gas in its host galaxies. Our result predicts that outflow feedback effects can be enhanced significantly when anisotropic pressure and a relatively powerful magnetic field is considered. Full article
(This article belongs to the Special Issue Black Hole Physics and Astrophysics)
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13 pages, 1541 KiB  
Article
The Brightest Point in Accretion Disk and Black Hole Spin: Implication to the Image of Black Hole M87*
by Vyacheslav I. Dokuchaev and Natalia O. Nazarova
Universe 2019, 5(8), 183; https://doi.org/10.3390/universe5080183 - 05 Aug 2019
Cited by 24 | Viewed by 4027
Abstract
We propose the simple new method for extracting the value of the black hole spin from the direct high-resolution image of black hole by using a thin accretion disk model. In this model, the observed dark region on the first image of the [...] Read more.
We propose the simple new method for extracting the value of the black hole spin from the direct high-resolution image of black hole by using a thin accretion disk model. In this model, the observed dark region on the first image of the supermassive black hole in the galaxy M87, obtained by the Event Horizon Telescope, is a silhouette of the black hole event horizon. The outline of this silhouette is the equator of the event horizon sphere. The dark silhouette of the black hole event horizon is placed within the expected position of the black hole shadow, which is not revealed on the first image. We calculated numerically the relation between the observed position of the black hole silhouette and the brightest point in the thin accretion disk, depending on the black hole spin. From this relation, we derive the spin of the supermassive black hole M87*, a = 0.75 ± 0.15 . Full article
(This article belongs to the Special Issue Black Hole Physics and Astrophysics)
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10 pages, 254 KiB  
Article
Quantum Complexity and Chaos in Young Black Holes
by Alexander Y. Yosifov and Lachezar G. Filipov
Universe 2019, 5(4), 93; https://doi.org/10.3390/universe5040093 - 22 Apr 2019
Cited by 7 | Viewed by 2654
Abstract
We argue that the problem of calculating retention time scales in young black holes is a problem of relative state complexity. In particular, we suggest that Alice’s ability to estimate the time scale for a perturbed black hole to release the extra n [...] Read more.
We argue that the problem of calculating retention time scales in young black holes is a problem of relative state complexity. In particular, we suggest that Alice’s ability to estimate the time scale for a perturbed black hole to release the extra n qubits comes down to her decoding the Hilbert space of the Hawking radiation. We then demonstrate the decoding task Alice faces is very difficult, and in order to calculate the relative state complexity she would either need to act with an exponentially complex unitary operator or apply an extremely fine-tuned future precursor operator to the perturbed state in S U ( 2 K ) . Full article
(This article belongs to the Special Issue Black Hole Physics and Astrophysics)
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