AGN torus threaded by large scale magnetic field

2018 ◽  
Vol 27 (10) ◽  
pp. 1844006
Author(s):  
A. Dorodnitsyn ◽  
T. Kallman
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Accretion Disk ◽  
Large Scale ◽  
Three Dimensional ◽  
X Ray ◽  
Radiative Feedback ◽  
Large Scale Magnetic Field ◽  
Three Dimensional Simulations

Large scale magnetic field can be easily dragged from galactic scales toward AGN along with accreting gas. There, it can contribute to both the formation of AGN “torus” and help to remove angular momentum from the gas which fuels AGN accretion disk. However the dynamics of such gas is also strongly influenced by the radiative feedback from the inner accretion disk. Here we present results from the three-dimensional simulations of pc-scale accretion which is exposed to intense X-ray heating.

scholarly journals Coronal ejections from convective spherical shell dynamos

2011 ◽  
Vol 7 (S286) ◽  
pp. 154-158 ◽  
Author(s):  
J. Warnecke ◽  
P. J. Käpylä ◽  
M. J. Mantere ◽  
A. Brandenburg
Keyword(s):  
Magnetic Field ◽  
Spherical Shell ◽  
Large Scale ◽  
Convection Zone ◽  
Three Dimensional ◽  
Simplified Model ◽  
Spherical Coordinates ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Large Scale Magnetic Field

AbstractWe present a three-dimensional model of rotating convection combined with a simplified model of a corona in spherical coordinates. The motions in the convection zone generate a large-scale magnetic field which is sporadically ejected into the outer layers above. Our model corona is approximately isothermal, but it includes density stratification due to gravity.

scholarly journals Magnetic Flux Transport in Protostellar Accretion Disks

1997 ◽  
Vol 163 ◽  
pp. 692-692
Author(s):  
John Contopoulos ◽  
Arieh Königl
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Accretion Disks ◽  
Large Scale ◽  
Turbulent Viscosity ◽  
Flux Transport ◽  
Disk Structure ◽  
Large Scale Magnetic Field ◽  
Field Lines ◽  
Open Magnetic Field

AbstractCentrifugally driven winds from the surfaces of magnetized accretion disks are a leading candidate for the origin of bipolar outflows and have also been recognized as an attractive mechanism for removing the angular momentum of the accreted matter. The origin of the open magnetic field lines that thread the disk in this scenario is, however, still uncertain. One possibility is that the field lines are transported through the disk, but previous studies have shown that this process is inefficient in disks with turbulent viscosity and diffusivity. Here we examine whether the efficiency can be increased if angular momentum is transported from the disk surfaces by large-scale magnetic fields instead of radially by viscous stresses. In this picture, the removal of angular momentum is associated with the establishment of a global poloidal electric current driven by the radial EMF in the disc, and it does not necessarily need to involve super-Alfvénic outflows. We address this problem in the context of protostellar systems and present representative solutions of the time evolution of a resistive disk that is initially threaded by a uniform vertical field anchored at a large distance from its surfaces. We assume that the angular momentum transport in the disk is controlled by the large-scale magnetic field and take into account the influence of the field on the disk structure.

scholarly journals ACCRETION DISKS WITH A LARGE SCALE MAGNETIC FIELD AROUND BLACK HOLES

2013 ◽  
Vol 53 (A) ◽  
pp. 677-682
Author(s):  
Gennady Bisnovatyi-Kogan ◽  
Alexandr S. Klepnev ◽  
Richard V.E. Lovelace
Keyword(s):  
Magnetic Field ◽  
Black Holes ◽  
Accretion Disk ◽  
Accretion Disks ◽  
Large Scale ◽  
Outward Diffusion ◽  
Large Scale Magnetic Field ◽  
Jet Collimation ◽  
The Magnetic Field ◽  
Inner Parts

We consider accretion disks around black holes at high luminosity, and the problem of the formation of a large-scale magnetic field in such disks, taking into account the non-uniform vertical structure of the disk. The structure of advective accretion disks is investigated, and conditions for the formation of optically thin regions in central parts of the accretion disk are found. The high electrical conductivity of the outer layers of the disk prevents outward diffusion of the magnetic field. This implies a stationary state with a strong magnetic field in the inner parts of the accretion disk close to the black hole, and zero radial velocity at the surface of the disk. The problem of jet collimation by magneto-torsion oscillations is investigated.

On the measurement of the turbulent diffusivity of a large-scale magnetic field

2013 ◽  
Vol 717 ◽  
pp. 347-360 ◽  
Author(s):  
S. M. Tobias ◽  
F. Cattaneo
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Laboratory Experiments ◽  
Three Dimensional ◽  
Effective Diffusivity ◽  
Dimensional System ◽  
Two Dimensional ◽  
Electrically Conducting ◽  
State Response ◽  
Large Scale Magnetic Field

AbstractWe argue that a method developed by Ångström (Ann. Phys. Chem., vol. 114, 1861, pp. 513–530) to measure the thermal conductivity of solids can be adapted to determine the effective diffusivity of a large-scale magnetic field in a turbulent electrically conducting fluid. The method consists of applying an oscillatory source and measuring the steady-state response. We illustrate this method in a two-dimensional system. This geometry is chosen because it is possible to compare the results with independent methods that are restricted to two-dimensional flows. We describe two variants of this method: one (the ‘turbulent Ångström method’) that is better suited to laboratory experiments and a second (the ‘method of oscillatory sines’) that is effective for numerical experiments. We show that, if correctly implemented, all methods agree. Based on these results we argue that these methods can be extended to three-dimensional numerical simulations and laboratory experiments.

scholarly journals Three-Dimensional Simulations of Accretion Disks

1997 ◽  
Vol 163 ◽  
pp. 179-189 ◽  
Author(s):  
John F. Hawley ◽  
Steven A. Balbus
Keyword(s):  
Angular Momentum ◽  
Accretion Disk ◽  
Accretion Disks ◽  
Three Dimensional ◽  
Spiral Waves ◽  
Central Issue ◽  
Transport Mechanisms ◽  
Mhd Turbulence ◽  
Mhd Instability ◽  
Three Dimensional Simulations

AbstractThe transport of angular momentum is the central issue in accretion disk dynamics. We review recent three-dimensional simulations that investigate possible transport mechanisms. Purely hydrodynamic local instabilities and turbulence are ruled out; global spiral waves remain a possibility. MHD turbulence, arising from a local MHD instability, has been shown effective in transporting angular momentum at dynamically important rates. These results establish the basic picture of accretion disk transport.

SELF-ASSEMBLED COBALT CHAINS INDUCED BY MAGNETIC FIELD THROUGH HYDROTHERMALLY REDUCING COBALT IONS

2011 ◽  
Vol 25 (32) ◽  
pp. 4323-4329 ◽  
Author(s):  
FAN ZHAO ◽  
MIN YAO ◽  
JUN WANG
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Three Dimensional ◽  
Vibrating Sample Magnetometer ◽  
X Ray Diffraction ◽  
Cross Sectional ◽  
Cobalt Ions ◽  
X Ray ◽  
Hierarchical Microspheres ◽  
Potential Applications

Co uniform hierarchical microspheres were grown on a large scale at 200° by a simple hydrothermal method with the help of the surfactant polyvinylpyrrolidone (PVP). During the synthesis, the external magnetic field as a controlling factor assembled cobalt microspheres to form chain-like structures vertically on substrate. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the product. The results indicate that three-dimensional (3D) Co microspheres are constructed by the cross-sectional nanoplatelets shape with a mean thickness of ~ 250 nm. The mechanism involved for the formation of the chain-like structures is discussed. The results of the vibrating sample magnetometer (VSM) show that the magnetic Co chains possess the saturation magnetization of 125.2 emu/g. Our work may shed some light on the design of other well-defined complex nanostructures, and as-grown architectures may have potential applications.

scholarly journals Gravo-Magnetodynamic Engine for Cosmic Jets

1990 ◽  
Vol 140 ◽  
pp. 425-430 ◽  
Author(s):  
Yutaka Uchida
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Large Scale ◽  
Gravitational Energy ◽  
Central Object ◽  
Disk Material ◽  
Large Scale Magnetic Field

There is a long-standing mystery about the formation of the jets and lobes from AGN's. In the present paper, a “gravo-magnetodynamic” picture is proposed for the production of the jets and lobes from AGN's: The primordial large scale magnetic field, which is squeezed by the gravitational contraction of the material to the central object, serves in driving out the spinning jets in bipolar directions, and at the same time, serves as a drain extracting angular momentum of the disk material, enhancing the accretion and therefore enhancing the liberation of the gravitational energy at the center.

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