scholarly journals Accretion Disk Electrodynamics

1985 ◽  
Vol 107 ◽  
pp. 453-469 ◽  
Author(s):  
F. V. Coroniti
Keyword(s):  
Magnetic Field ◽  
Black Holes ◽  
Black Hole ◽  
Accretion Disk ◽  
Large Scale ◽  
Relativistic Jet ◽  
Scale Field ◽  
Magnetic Buoyancy ◽  
Large Scale Field ◽  
Viscous Transport

Accretion disk electrodynamic phenomenae are separable into two classes: 1) disks and coronae with turbulent magnetic fields; 2) disks and black holes which are connected to a large-scale external magnetic field. Turbulent fields may originate in an α - ω dynamo, provide anomalous viscous transport, and sustain an active corona by magnetic buoyancy. The large-scale field can extract energy and angular momentum from the disk and black hole, and be dynamically configured into a collimated relativistic jet.

scholarly journals The Magnetic Field Near the Local Bubble

1997 ◽  
Vol 166 ◽  
pp. 227-238
Author(s):  
Carl Heiles
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Zeeman Splitting ◽  
Relativistic Electrons ◽  
Local Bubble ◽  
Scale Field ◽  
Large Scale Field ◽  
Field Lines ◽  
Hi Shells ◽  
The Magnetic Field

AbstractThere are almost no direct observational indicators of the magnetic field inside the local bubble. Just outside the bubble, the best tracers are stellar polarization and HI Zeeman splitting. These show that the local field does not follow the large-scale Galactic field. Here we discuss whether the deformation of the large-scale field by the local HI shells is consistent with the observations. We concentrate on the Loop 1 region, and find that the field lines are well-explained by this idea; in addition, the bright radio filaments of Radio Loop 1 delineate particular field lines that are “lit up” by an excess of relativistic electrons.

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.

scholarly journals Advection/diffusion of large scale magnetic field in accretion disks

2009 ◽  
Vol 16 (1) ◽  
pp. 77-81 ◽  
Author(s):  
R. V. E. Lovelace ◽  
G. S. Bisnovatyi-Kogan ◽  
D. M. Rothstein
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Turbulent Viscosity ◽  
Pressure Ratio ◽  
Rotational Instability ◽  
Small Scale ◽  
Magnetic Diffusivity ◽  
Large Scale Magnetic Field ◽  
Scale Field ◽  
Large Scale Field

Abstract. Activity of the nuclei of galaxies and stellar mass systems involving disk accretion to black holes is thought to be due to (1) a small-scale turbulent magnetic field in the disk (due to the magneto-rotational instability or MRI) which gives a large viscosity enhancing accretion, and (2) a large-scale magnetic field which gives rise to matter outflows and/or electromagnetic jets from the disk which also enhances accretion. An important problem with this picture is that the enhanced viscosity is accompanied by an enhanced magnetic diffusivity which acts to prevent the build up of a significant large-scale field. Recent work has pointed out that the disk's surface layers are non-turbulent and thus highly conducting (or non-diffusive) because the MRI is suppressed high in the disk where the magnetic and radiation pressures are larger than the thermal pressure. Here, we calculate the vertical (z) profiles of the stationary accretion flows (with radial and azimuthal components), and the profiles of the large-scale, magnetic field taking into account the turbulent viscosity and diffusivity due to the MRI and the fact that the turbulence vanishes at the surface of the disk. We derive a sixth-order differential equation for the radial flow velocity vr(z) which depends mainly on the midplane thermal to magnetic pressure ratio β>1 and the Prandtl number of the turbulence P=viscosity/diffusivity. Boundary conditions at the disk surface take into account a possible magnetic wind or jet and allow for a surface current in the highly conducting surface layer. The stationary solutions we find indicate that a weak (β>1) large-scale field does not diffuse away as suggested by earlier work.

scholarly journals A global view of the inner accretion and ejection flow around super massive black holes

2019 ◽  
Vol 630 ◽  
pp. A94 ◽  
Author(s):  
Margherita Giustini ◽  
Daniel Proga
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Absorption Line ◽  
Accretion Disk ◽  
Large Scale ◽  
Black Hole Mass ◽  
Broad Absorption ◽  
Massive Black Holes ◽  
Broad Absorption Line ◽  
Global View

Context. Understanding the physics and geometry of accretion and ejection around super massive black holes (SMBHs) is important to understand the evolution of active galactic nuclei (AGN) and therefore of the large scale structures of the Universe. Aims. We aim at providing a simple, coherent, and global view of the sub-parsec accretion and ejection flow in AGN with varying Eddington ratio, ṁ, and black hole mass, MBH. Methods. We made use of theoretical insights, results of numerical simulations, as well as UV and X-ray observations to review the inner regions of AGN by including different accretion and ejection modes, with special emphasis on the role of radiation in driving powerful accretion disk winds from the inner regions around the central SMBH. Results. We propose five ṁ regimes where the physics of the inner accretion and ejection flow around SMBHs is expected to change, and that correspond observationally to quiescent and inactive galaxies; low luminosity AGN (LLAGN); Seyferts and mini-broad absorption line quasars (mini-BAL QSOs); narrow line Seyfert 1 galaxies (NLS1s) and broad absorption line quasars (BAL QSOs); and super-Eddington sources. We include in this scenario radiation-driven disk winds, which are strong in the high ṁ, large MBH regime, and possibly present but likely weak in the moderate ṁ, small MBH regime. Conclusions. A great diversity of the accretion/ejection flows in AGN can be explained to a good degree by varying just two fundamental properties: the Eddington ratio ṁ and the black hole mass MBH, and by the inclusion of accretion disk winds that can naturally be launched by the radiation emitted from luminous accretion disks.

scholarly journals The Observed Characteristics of the Local Magnetic Field

1974 ◽  
Vol 60 ◽  
pp. 137-150 ◽  
Author(s):  
J. B. Whiteoak
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Galactic Plane ◽  
Background Radiation ◽  
Field Structure ◽  
Local Magnetic Field ◽  
Field Parallel ◽  
Scale Field ◽  
Large Scale Field ◽  
Galactic Background

The main investigations of the local magnetic field are reviewed and are found to contain some conflict in interpretation. At radio wavelengths, studies have been made using both the Faraday rotation of the polarized radiation from extragalactic sources and pulsars, and the polarization of the galactic background radiation. With the former type of observation, although more data are available for extragalactic sources, any interpretation may be complicated by the influence of distant field structure. The results are consistent with a large-scale field parallel to the galactic plane, with a field strength of about 2 µG, and which is directed towards l=90°. This field contains irregularities in direction and strength on a scale of about 100–200 pc. The polarization of galactic background radiation may yield the most detailed information about the local field structure – the results to date show loops of magnetic fields extending along the radio spurs.The interpretation in terms of small-scale irregularities embedded in a large-scale field parallel to the galactic plane differs from that proposed to explain the optical polarization of starlight, in which a helical field configuration near the Sun was preferred to a more disordered pattern.

scholarly journals Identifying solar-like magnetic cycles with Zeeman-Doppler-Imaging

2020 ◽  
Vol 500 (1) ◽  
pp. 1243-1260
Author(s):  
L T Lehmann ◽  
G A J Hussain ◽  
A A Vidotto ◽  
M M Jardine ◽  
D H Mackay
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Large Scale ◽  
Doppler Imaging ◽  
Small Scale ◽  
Flux Emergence ◽  
Flux Transport ◽  
Scale Field ◽  
Large Scale Field ◽  
Magnetic Cycles

ABSTRACT We are reaching the point where spectropolarimetric surveys have run for long enough to reveal solar-like magnetic activity cycles. In this paper, we investigate what would be the best strategy to identify solar-like magnetic cycles and ask which large-scale magnetic field parameters best follow a solar-type magnetic cycle and are observable with the Zeeman-Doppler-Imaging (ZDI) technique. We approach these questions using the 3D non-potential flux transport simulations of Yeates & Mackay (2012) modelling the solar vector magnetic field over 15 yr (centred on solar cycle 23). The flux emergence profile was extracted from solar synoptic maps and used as input for a photospheric flux transport model in combination with a non-potential coronal evolution model. We synthesize spectropolarimetric data from the simulated maps and reconstruct them using ZDI. The ZDI observed solar cycle is set into the context of other cool star observations and we present observable trends of the magnetic field topology with time, sunspot number, and S-index. We find that the axisymmetric energy fraction is the best parameter of the ZDI detectable large-scale field to trace solar-like cycles. Neither the surface averaged large-scale field or the total magnetic energy is appropriate. ZDI seems also to be able to recover the increase of the toroidal energy with S-index. We see further that ZDI might unveil hints of the dynamo modes that are operating and of the global properties of the small-scale flux emergence like active latitudes.

scholarly journals On the Magnetic Field Inside the Solar Circle of the Galaxy: on the Possibility of Investigation of Some of Characteristics of the Interstellar Medium Using Pulsars with Large Faraday Rotation Values

2018 ◽  
pp. 353-363
Author(s):  
R. R. Andreasyan ◽  
H. R. Andreasyan ◽  
G. M. Paronyan
Keyword(s):  
Magnetic Field ◽  
Interstellar Medium ◽  
Faraday Rotation ◽  
Large Scale ◽  
Circular Model ◽  
Scale Field ◽  
The Galaxy ◽  
Large Scale Field ◽  
The Magnetic Field ◽  
Galactic Distribution

To study some characteristics of the interstellar medium, observational data of pulsars with large Faraday rotation values (|RM| > 300 rad / m2) were used. It was suggested and justified that large |RM|values can be due to the contribution of the regions with increased electron concentration, projected on the pulsar. Most likely these are the HII regions, dark nebulae and molecular clouds. In these objects the magnetic field can be oriented in the direction of a large-scale field of the Galaxy, or simply is a deformed extension of the galactic field. It was shown that the Galactic distribution of rotation measures of pulsars with|RM|>300 rad/m2 corresponds to the circular model of the magnetic field of the Galaxy, with the counter-clockwise direction of the magnetic field in the galactocentric circle 5 kpc < R < 7 kpc.

Fluctuations in the Galactic Magnetic Field

1990 ◽  
Vol 140 ◽  
pp. 55-58
Author(s):  
James M. Cordes ◽  
Andrew Clegg ◽  
John Simonetti
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Measure Data ◽  
Small Scale ◽  
Radio Sources ◽  
Galactic Magnetic Field ◽  
Rotation Measure ◽  
Scale Field ◽  
Large Scale Field ◽  
The Magnetic Field

We discuss small scale structure in the Galactic magnetic field as inferred from Faraday rotation measurements of extragalactic radio sources. The rotation measure data suggest a continuum of length scales extending from parsec scales down to at least 0.01 pc and perhaps to as small as 109 cm. Such turbulence in the magnetic field comprises a reservoir of energy that is comparable to the energy in the large scale field.

scholarly journals Global magnetic fields: variation of solar minima

2011 ◽  
Vol 7 (S286) ◽  
pp. 113-122
Author(s):  
Andrey G. Tlatov ◽  
Vladimir N. Obridko
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Sunspot Cycle ◽  
Magnetic Activity ◽  
Small Scale ◽  
The Sun ◽  
Large Scale Magnetic Field ◽  
Scale Field ◽  
Large Scale Field

AbstractThe topology of the large-scale magnetic field of the Sun and its role in the development of magnetic activity were investigated using Hα charts of the Sun in the period 1887-2011. We have considered the indices characterizing the minimum activity epoch, according to the data of large-scale magnetic fields. Such indices include: dipole-octopole index, area and average latitude of the field with dominant polarity in each hemisphere and others. We studied the correlation between these indices and the amplitude of the following sunspot cycle, and the relation between the duration of the cycle of large-scale magnetic fields and the duration of the sunspot cycle.The comparative analysis of the solar corona during the minimum epochs in activity cycles 12 to 24 shows that the large-scale magnetic field has been slow and steadily changing during the past 130 years. The reasons for the variations in the solar coronal structure and its relation with long-term variations in the geomagnetic indices, solar wind and Gleissberg cycle are discussed.We also discuss the origin of the large-scale magnetic field. Perhaps the large-scale field leads to the generation of small-scale bipolar ephemeral regions, which in turn support the large-scale field. The existence of two dynamos: a dynamo of sunspots and a surface dynamo can explain phenomena such as long periods of sunspot minima, permanent dynamo in stars and the geomagnetic field.

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