scholarly journals Dissipation of Turbulent Magnetic Fields in Accreting Black Holes

1997 ◽  
Vol 163 ◽  
pp. 749-750 ◽  
Author(s):  
Victor Kowalenko ◽  
Fulvio Melia
Keyword(s):  
Magnetic Field ◽  
Black Holes ◽  
Black Hole ◽  
Magnetic Fields ◽  
Magnetic Field Intensity ◽  
Tearing Mode ◽  
Massive Black Hole ◽  
Basic Principles ◽  
Alternative Approach ◽  
The Magnetic Field

AbstractCalculations of the spectrum resulting from accretion onto a massive black hole often make use of the “equipartition assumption” in order to estimate the magnetic field intensity. Thus, the mechanism for the dissipation of the magnetic field and the resulting dynamical influence on the gas have not been treated quantitatively, nor self-consistently. Here, we introduce an alternative approach for modelling the magnetic field dissipation from basic principles, using current ideas about turbulent fields and tearing mode instabilities.

scholarly journals Very High-Energy Emission from the Direct Vicinity of Rapidly Rotating Black Holes

Galaxies ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 122 ◽  
Author(s):  
Kouichi Hirotani
Keyword(s):  
Magnetic Field ◽  
Black Holes ◽  
Black Hole ◽  
Electric Field ◽  
Gamma Rays ◽  
Accretion Rate ◽  
High Energy ◽  
Relativistic Electrons ◽  
Field Lines ◽  
The Magnetic Field

When a black hole accretes plasmas at very low accretion rate, an advection-dominated accretion flow (ADAF) is formed. In an ADAF, relativistic electrons emit soft gamma-rays via Bremsstrahlung. Some MeV photons collide with each other to materialize as electron-positron pairs in the magnetosphere. Such pairs efficiently screen the electric field along the magnetic field lines, when the accretion rate is typically greater than 0.03–0.3% of the Eddington rate. However, when the accretion rate becomes smaller than this value, the number density of the created pairs becomes less than the rotationally induced Goldreich–Julian density. In such a charge-starved magnetosphere, an electric field arises along the magnetic field lines to accelerate charged leptons into ultra-relativistic energies, leading to an efficient TeV emission via an inverse-Compton (IC) process, spending a portion of the extracted hole’s rotational energy. In this review, we summarize the stationary lepton accelerator models in black hole magnetospheres. We apply the model to super-massive black holes and demonstrate that nearby low-luminosity active galactic nuclei are capable of emitting detectable gamma-rays between 0.1 and 30 TeV with the Cherenkov Telescope Array.

scholarly journals Alternative Approach for the Calculation of Magnetic Field due to Magnet for Magnetic Field Visualization and Evaluation

2020 ◽  
Vol 15 (1) ◽  
pp. 150-160
Author(s):  
Kishor Kaphle ◽  
Gyanendra Karki ◽  
Amrit Panthi
Keyword(s):  
Magnetic Field ◽  
Permanent Magnet ◽  
Field Distribution ◽  
Permanent Magnets ◽  
Magnetic Field Distribution ◽  
Geometrical Shape ◽  
Shape Transformation ◽  
Basic Principles ◽  
Alternative Approach ◽  
The Magnetic Field

 The magnetic field of different geometry of the permanent magnet is analytically calculated by using basic principles of the magnetism in very easier approach. Concept of origin shifting and geometrical shape transformation are used to formulate the formula for cuboidal, cubical and cylindrical permanent magnets. This concept can be used for the analysis of magnetic field distribution in space around for permanent magnet as well as electromagnet in a very easier approach. Handy and simplified software is made to calculate the magnetic field due to permanent magnet and electromagnet at any desired position on space. Magnetic field visualization is also done in both magnitude and direction by using MATLAB.  

scholarly journals No-z model: results and perspectives for accretion discs

2021 ◽  
pp. 490-494
Author(s):  
E. A. Mikhailov ◽  
M. V. Pashentsevay
Keyword(s):  
Magnetic Field ◽  
Black Holes ◽  
Magnetic Fields ◽  
Variable Stars ◽  
Field Structure ◽  
Accretion Discs ◽  
Astrophysical Objects ◽  
The Galaxy ◽  
Galaxy Center ◽  
The Magnetic Field

Accretion discs surround different compact astrophysical objects such as black holes, neutron stars and white dwarfs. Also they are situated in systems of variable stars and near the galaxy center. Magnetic fields play an important role in evolution and hydrodynamics of the accretion discs: for example, they can describe such processes as the transition of the angular momentum. There are different approaches to explain the magnetic fields, but most interesting of them are connected with dynamo generation. As for disc, it is quite useful to take no-$z$ approximation which has been developed for galactic discs to solve the dynamo equations. It takes into account that the disc is quite thin, and we can solve the equations only for two plane components of the field. Here we describe the time dependence of the magnetic field for different distances from the center of the disc. Also we compare the results with another approaches which take into account more complicated field structure.

scholarly journals Generation of Magnetic Fields in Accreting Systems as a Basis of Nonthermal Mode of Energy Release

1993 ◽  
Vol 157 ◽  
pp. 197-201
Author(s):  
L.A. Pustil'Nik ◽  
N.R. Ikhsanov
Keyword(s):  
Magnetic Field ◽  
Black Hole ◽  
Magnetic Fields ◽  
Energy Release ◽  
Polar Region ◽  
High Energy ◽  
Ultra High Energy ◽  
The Magnetic Field

Generation of the magnetic field during procces of disc accretion onto black hole or magnetize neutrin star may form current structures in a polar region. The instability and disruption of this currents must lead to effective acceleration of the particles to ultra high energy as it observe by GRO and UHE-astronomy experiments.

scholarly journals CONSTRAINTS ON X-RAY POLARIZATION OF SYNCHROTRON JETS FROM STELLAR-MASS BLACK HOLES

2012 ◽  
Vol 08 ◽  
pp. 102-107
Author(s):  
D. M. RUSSELL
Keyword(s):  
Magnetic Field ◽  
Black Holes ◽  
Black Hole ◽  
Synchrotron Emission ◽  
Relativistic Jets ◽  
X Ray ◽  
Linearly Polarized ◽  
Hard State ◽  
X Ray Binaries ◽  
The Magnetic Field

For most black hole X-ray binaries, the fraction of X-ray flux originating in the synchrotron jets is generally thought to be low in the hard state. However in one intriguing case, the infrared – X-ray correlations, evolution of broadband spectra and timing signatures suggest that synchrotron emission from a jet likely dominated both the infrared and X-ray flux on the hard state decline of an outburst of XTE J1550–564 at a luminosity of ~ (2 × 10-4 – 2 × 10-3) L Edd . Synchrotron emission from the relativistic jets launched close to black holes can be highly linearly polarized, depending on the configuration of the magnetic field. It has recently been shown that the polarimetric signature of their jets is detected in the infrared and is highly variable. This reveals the magnetic geometry in a region of the compact jet near its base, close to the black hole. From these results, it is predicted that in some cases, high (possibly up to 10%), variable levels of X-ray polarization from synchrotron emission originating in jets will be detected from accreting black holes by future spaceborne X-ray polarimeters.

scholarly journals Electrically-charged black holes and the Blandford-Znajek mechanism

2021 ◽  
Author(s):  
Serguei S Komissarov
Keyword(s):  
Magnetic Field ◽  
Black Holes ◽  
Black Hole ◽  
Electric Charge ◽  
Meissner Effect ◽  
Charged Black Holes ◽  
Field Lines ◽  
The One ◽  
Electrically Charged ◽  
The Magnetic Field

Abstract Recently, it was claimed by King & Pringle that accretion of electric charge by a black hole rotating in an aligned external magnetic field results in a “dead” vacuum magnetosphere, where the electric field is totally screened, no vacuum breakdown is possible, and the Blandford-Znajek mechanism cannot operate. Here we study in details the properties of the Wald solution for electrically charged black holes discussed in their paper. Our results show that the claim is erroneous as in the solution with the critical charge q0 = 2aB0 there exists a drop of electrostatic potential along all magnetic field lines except the one coinciding with the symmetry axis. It is also found that while uncharged rotating black holes expel external vacuum magnetic field from their event horizon (the Meissner effect), electric charging of black holes pulls the magnetic field lines back on it, resembling what has been observed in some previous force-free, RMHD and PIC simulations of black hole magnetospheres. This suggests that accretion of electric charge may indeed be a feature of the black hole electrodynamics. However, our analysis shows that the value q0 of the BH charge given by Wald is likely to be only an upper limit, and that the actual value depends of the details of the magnetospheric physics.

scholarly journals Correlation between Ca plages and longitudinal magnetic fields of the CSSAR active regions

1968 ◽  
Vol 35 ◽  
pp. 338-345 ◽  
Author(s):  
V. Bumba ◽  
G. Godoli
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Intensity ◽  
Solar Disk ◽  
Magnetic Field Intensity ◽  
Active Regions ◽  
The Magnetic Field ◽  
Magnetic Inclusions

The shapes of K2,3,2 Ca plages and longitudinal magnetic fields are compared for CSSAR active regions during their first transit on the solar disk.The bipolar magnetic regions follow the Hale polarity law.Often the region of inversion of the magnetic field corresponds to a gap in the Ca plage structure.Bright patches of plages may coincide with magnetic inclusions, magnetic hills, and occasionally also with regions of inversion of the magnetic field. The outline of Ca plages follow well the isogauss of 20–40 oersted.Histograms of the distances of individual magnetic field intensity peaks do not only correspond to the geometry of the supergranular network but also seem to indicate a difference in the organization of these peaks between the leading and following polarities.

scholarly journals Condensation of Neutral Vector Bosons with Magnetic Moment

2017 ◽  
Vol 45 ◽  
pp. 1760047 ◽  
Author(s):  
Gretel Quintero Angulo ◽  
Aurora Pérez Martínez ◽  
Hugo Pérez Rojas
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Moment ◽  
Magnetic Field Intensity ◽  
Rest Mass ◽  
Critical Value ◽  
Equation Of Motion ◽  
Vector Bosons ◽  
Neutral Vector ◽  
The Magnetic Field

We study the equation of motion of neutral vector bosons bearing a magnetic moment (MM). The effective rest mass of vector bosons is a decreasing function of the magnetic field intensity. Consequently a diffuse condensation of the bosons appears below a critical value of the field. For typical values of densities and magnetic fields the magnetization is positive and the neutral boson system can maintain a magnetic field self-consistently. A discussion of the relevance in astrophysics is presented.

Estimation of informative and background signals ratio in the registration of magnetic fields of surface defects by magnetic measuring transducers

2020 ◽  
pp. 43-49
Author(s):  
Yuriy L. Nikolaev ◽  
Elina F. Akhmetshina ◽  
Aleksey A. Samorukov ◽  
Aleksandra V. Chernova
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Intensity ◽  
Output Signal ◽  
Magnetic Field Intensity ◽  
Background Ratio ◽  
Estimated Parameters ◽  
Magnetic Measuring ◽  
Background Magnetic Field ◽  
The Magnetic Field

Authors propose algorithms for quantitative ratio determining of informative and background components of the output signal of magnetic measuring transducers, used as a means of recording and measuring the parameters of locally distributed magnetic fields that occur over defective surface areas of the tested object in an applied permanent magnetic field. The method of separating the informative and background components based on the summation property and the deterministic nature of the distributions of the magnetic field intensity of the defect and the background magnetic field along the coordinate axis parallel to the controlled surface, and analysis of the topography of the distribution of magnetic field intensity is described. The approach to selection and experimental determination of estimated parameters characterizing the levels of informative and background signals is justified. Authors give the formulas for calculating the signal-to-background ratio based on the measured values of the estimated parameters applied to single magnet-static, differential magnet-static and differentiating magnetic measuring transducers taking into account the orientation direction (normal, tangential) of their sensitivity axis. The signal-to-background ratio calculation results are presented using an example of an analysis of the magnetic measuring transducers output signal when registering the distribution of the magnetic field intensity over the surface of a control sample with artificial defects of a given size. The comparative analysis of considered magnetic measuring transducers according to signal-to-background ratio is carried out. General recommendations to increase the value of the signal-to-background ratio parameter are given.

scholarly journals The Role of Magnetic Fields in the Origin and Structure of Planetary Nebulae

1968 ◽  
Vol 34 ◽  
pp. 279-281
Author(s):  
Donald H. Menzel
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Intensity ◽  
Magnetic Field Intensity ◽  
Planetary Nebulae ◽  
Ionized Gas ◽  
Symmetrical Structure ◽  
Image Position ◽  
The Magnetic Field

That the characteristic, quasi-symmetrical structure of planetary nebulae may result from the presence of imbedded magnetic fields has undoubtedly occurred to many astronomers. Gurzadian (1962), for example, employed the widely used equation where p is the pressure of the ionized gas and H the magnetic-field intensity. This equation specifies that the sum of the gas and magnetic pressures should be constant for a given value of the radius.

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