scholarly journals Time evolution of the large-scale tail of nonhelical primordial magnetic fields with back-reaction of the turbulent medium

2012 ◽  
Vol 86 (10) ◽  
Author(s):  
Andrey Saveliev ◽  
Karsten Jedamzik ◽  
Günter Sigl
Keyword(s):  
Magnetic Fields ◽  
Time Evolution ◽  
Large Scale ◽  
Turbulent Medium ◽  
Back Reaction ◽  
Primordial Magnetic Fields

scholarly journals 3D numerical simulations of magnetic field evolution in barred galaxies and in spiral galaxies under influence of tidal forces

2010 ◽  
Vol 6 (S274) ◽  
pp. 381-384
Author(s):  
Katarzyna Otmianowska-Mazur ◽  
Katarzyna Kulpa-Dybeł ◽  
Barbara Kulesza-Żydzik ◽  
Hubert Siejkowski ◽  
Grzegorz Kowal
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Spiral Galaxies ◽  
Cosmic Ray ◽  
Mhd Equations ◽  
Back Reaction ◽  
Barred Galaxies ◽  
Tidal Forces ◽  
Field Evolution

AbstractWe present the results of the three-dimensional, fully non-linear MHD simulations of the large-scale magnetic field evolution in a barred galaxy with the back reaction of magnetic field to gas. We also include the process of the cosmic-ray driven dynamo. In addition, we check what physical processes are responsible for the magnetic field evolution in the tidally influenced spiral galaxies. We solve the MHD equations for the gas and magnetic field in a spiral galaxy with gravitationally prescribed bulge, disk and halo which travels along common orbit with the second body. In order to compare our modeling results with the observations we also construct the maps of high-frequency (Faraday rotation-free) polarized radio emission from the simulated magnetic fields. The model accounts for the effects of projection and limited resolution.We found that the obtained magnetic field configurations are highly similar to the observed maps of the polarized intensity of barred galaxies, because the modeled vectors form coherent structures along the bar and spiral arms. We also found a physical explanation of the problem of inconsistency between the velocity and magnetic fields character present in this type of galaxies. Due to the dynamical influence of the bar, the gas forms spiral waves which go radially outward. Each spiral arm forms the magnetic arm which stays much longer in the disk than the gaseous spiral structure. The modeled total energy of magnetic field and magnetic flux grows exponentially due to the action of the cosmic-ray driven dynamo. We also obtained the polarization maps of tidally influenced spiral galaxies which are similar to observations.

scholarly journals Seed magnetic fields in turbulent small-scale dynamos

2020 ◽  
Vol 499 (2) ◽  
pp. 2076-2086
Author(s):  
Amit Seta ◽  
Christoph Federrath
Keyword(s):  
Magnetic Fields ◽  
Random Field ◽  
Large Scale ◽  
Galaxy Cluster ◽  
Turbulent Medium ◽  
Small Scale ◽  
Uniform Field ◽  
Dynamo Action ◽  
Trace Back ◽  
Seed Field

ABSTRACT Magnetic fields in galaxies and galaxy clusters are amplified from a very weak seed value to the observed $\mu$G strengths by the turbulent dynamo. The seed magnetic field can be of primordial or astrophysical origin. The strength and structure of the seed field, on the galaxy or galaxy cluster scale, can be very different, depending on the seed-field generation mechanism. The seed field first encounters the small-scale dynamo, thus we investigate the effects of the strength and structure of the seed field on the small-scale dynamo action. Using numerical simulations of driven turbulence and considering three different seed-field configurations: (1) uniform field, (2) random field with a power-law spectrum, and (3) random field with a parabolic spectrum, we show that the strength and statistical properties of the dynamo-generated magnetic fields are independent of the details of the seed field. We demonstrate that, even when the small-scale dynamo is not active, small-scale magnetic fields can be generated and amplified linearly due to the tangling of the large-scale field. In the presence of the small-scale dynamo action, we find that any memory of the seed field for the non-linear small-scale dynamo generated magnetic fields is lost and thus, it is not possible to trace back seed-field information from the evolved magnetic fields in a turbulent medium.

scholarly journals Effects of primordial magnetic fields on CMB

2014 ◽  
Vol 10 (S306) ◽  
pp. 159-161 ◽  
Author(s):  
Héctor J. Hortúa ◽  
Leonardo Castañeda
Keyword(s):  
Magnetic Field ◽  
Perturbation Theory ◽  
Magnetic Fields ◽  
Large Scale ◽  
Unsolved Problem ◽  
Microwave Background ◽  
Cosmological Perturbation ◽  
Cosmological Perturbation Theory ◽  
Primordial Magnetic Fields ◽  
Primordial Magnetic Field

AbstractThe origin of large-scale magnetic fields is an unsolved problem in cosmology. In order to overcome, a possible scenario comes from the idea that these fields emerged from a small primordial magnetic field (PMF), produced in the early universe. This field could lead to the observed large-scales magnetic fields but also, would have left an imprint on the cosmic microwave background (CMB). In this work we summarize some statistical properties of this PMFs on the FLRW background. Then, we show the resulting PMF power spectrum using cosmological perturbation theory and some effects of PMFs on the CMB anisotropies.

scholarly journals Solar Magnetoconvection

1990 ◽  
Vol 138 ◽  
pp. 191-211
Author(s):  
Å. Nordlund ◽  
R. F. Stein
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Time Evolution ◽  
Large Scale ◽  
Stratified Medium ◽  
Small Scale ◽  
Surface Magnetic Field ◽  
The Hierarchical Structure ◽  
Surface Manifestation

As a prelude to discussing the interaction of magnetic fields with convection, we first review some general properties of convection in a stratified medium. Granulation, which is the surface manifestation of the major energy carrying convection scales, is a shallow phenomenon. Below the surface, the topology changes to one of filamentary cool downdrafts, immersed in a gently ascending isentropic background. The granular downflows merge into more widely separated downdrafts, on scales of mesogranulation and super-granulation.The local topology and time evolution of the small scale, kilo Gauss, network and facular magnetic field elements are controlled by convection on the scale of granulation. The topology and time evolution of larger scale magnetic field concentrations are controlled by the hierarchical structure of the horizontal components of the large scale velocity field. In sunspots, the small scale magnetic field structure determines the energy balance, the systematic flows and the waves. Below the surface, the small scale structure of the magnetic field may change drastically, with little observable effect at the surface. We discuss results of some recent numerical simulations of sunspot magnetic fields, and some mechanisms that may be relevant in determining the topology of the sub-surface magnetic field. Finally, we discuss the role of active region magnetic fields in the global solar dynamo.

scholarly journals Spin-Down of Solar-Type Stars with Internal Magnetic Fields

1993 ◽  
Vol 137 ◽  
pp. 464-468
Author(s):  
Paul Charbonneau ◽  
Keith B. Macgregor
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Differential Rotation ◽  
Large Scale ◽  
Back Reaction ◽  
Large Set ◽  
Large Scale Magnetic Field ◽  
Solar Type ◽  
Solar Type Star ◽  
Selection Of

AbstractWe present a selection of results from a large set of numerical simulations of the spin-down of a solar-type star containing a large scale magnetic field in its radiative interior. Our computations are dynamical, in that they take into account both the generation of the toroidal component by the wind-induced shear endits back-reaction on the azimuthal flow. Our results demonstrate the existence of classes of internal magnetic fields that can accomodate rapid spin-down near the ZAMS, and yield weak internal differential rotation by the solar age.

scholarly journals Large-Scale Flow Patterns in the Solar Atmosphere

1990 ◽  
Vol 142 ◽  
pp. 101-105
Author(s):  
K.R. Sivaraman
Keyword(s):  
Solar Cycle ◽  
Magnetic Fields ◽  
Time Evolution ◽  
Large Scale ◽  
Opposite Polarity ◽  
Meridional Flow ◽  
The Sun ◽  
Solar Cycle Variation ◽  
Large Scale Flow ◽  
Good Agreement

It is now well established (McIntosh 1979; Makarov and Sivaraman 1983) that the filament and filament channels seen in the H-alpha spectroheliograms (or filtergrams) can be used as reliable tracers for studying the time evolution of large-scale magnetic fields on the Sun. These features represent the neutral lines between the unipolar regions of opposite polarity. Comparison of the synoptic charts compiled from H-alpha pictures with those from full-disc magnetograms for the same period shows very good agreement and hence the former can be used with confidence for time evolution studies of large-scale unipolar regions for those periods when the magnetographs did not even exist. In this paper we shall present one of the results of our study (Makarov and Sivaraman 1983, 1989) on the migration of H-alpha filaments, namely, the existence of the meridional flow on the Sun. We shall extend it further to show the participation of this meridional flow in the solar cycle variation.

scholarly journals Tracing Primordial Magnetic Fields with 21 cm Line Observations

Galaxies ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 37 ◽  
Author(s):  
Kerstin Kunze
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Cosmic Microwave Background ◽  
Large Scale ◽  
Numerical Solutions ◽  
Gaussian Random Field ◽  
Microwave Background ◽  
Matter Power Spectrum ◽  
Primordial Magnetic Fields ◽  
The Universe

Magnetic fields are observed on a large range of scales in the universe. Up until recently, the evidence always pointed to magnetic fields associated with some kind of structure, from planets to clusters of galaxies. Blazar observations have been used to posit the first evidence of truly cosmological magnetic fields or void magnetic fields. A cosmological magnetic field generated in the very early universe before recombination has implications for the cosmic microwave background (CMB), large scale structure as well as the 21 cm line signal. In particular, the Lorentz term causes a change in the linear matter power spectrum. Its implication on the 21 cm line signal was the focus of our recent simulations which will be summarised here. Modelling the cosmological magnetic field as a gaussian random field numerical solutions were found for magnetic fields with present day amplitudes of 5 nG and negative spectral indices which are within the range of observational constraints imposed by the cosmic microwave background (CMB).

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