scholarly journals Magnetic field configurations in neutron stars from MHD simulations

2020 ◽  
Vol 495 (1) ◽  
pp. 1360-1371
Author(s):  
Ankan Sur ◽  
Brynmor Haskell ◽  
Emily Kuhn
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Neutron Stars ◽  
Magnetic Energy ◽  
Average Energy ◽  
Field Configuration ◽  
Exterior Boundary ◽  
Mhd Simulations ◽  
Non Linear ◽  
The Magnetic Field

ABSTRACT We have studied numerically the evolution of magnetic fields in barotropic neutron stars, by performing non-linear magnetohydrodynamical simulations with the code pluto. For both initially predominantly poloidal and toroidal fields, with varying strengths, we find that the field settles down to a mixed poloidal–toroidal configuration, where the toroidal component contributes between ${\rm 10}$ and $20 {{\ \rm per\ cent}}$ of the total magnetic energy. This is, however, not a strict equilibrium, as the instability leads to the development of turbulence, which, in turn, gives rise to an inverse helicity cascade, which determines the final ‘twisted torus’ setup. The final field configuration is thus dictated by the non-linear saturation of the instability, and is not stationary. The average energy of the poloidal and toroidal components, however, is approximately stable in our simulations, and a complex multipolar structure emerges at the surface, while the magnetic field is dipolar at the exterior boundary, outside the star.

scholarly journals 3D-MHD simulations of the evolution of magnetic fields in FR II radio sources

2010 ◽  
Vol 6 (S275) ◽  
pp. 170-171
Author(s):  
Martín Huarte-Espinosa ◽  
Martin Krause ◽  
Paul Alexander
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Numerical Simulations ◽  
Magnetic Structure ◽  
Magnetic Energy ◽  
Power Spectra ◽  
Radio Sources ◽  
Viewing Angle ◽  
Mhd Simulations ◽  
The Magnetic Field

Abstract3D-MHD numerical simulations of bipolar, hypersonic, weakly magnetized jets and synthetic synchrotron observations are presented to study the structure and evolution of magnetic fields in FR II radio sources. The magnetic field setup in the jet is initially random. The power of the jets as well as the observational viewing angle are investigated. We find that synthetic polarization maps agree with observations and show that magnetic fields inside the sources are shaped by the jets' backflow. Polarimetry statistics correlates with time, the viewing angle and the jet-to-ambient density contrast. The magnetic structure inside thin elongated sources is more uniform than for ones with fatter cocoons. Jets increase the magnetic energy in cocoons, in proportion to the jet velocity. Both, filaments in synthetic emission maps and 3D magnetic power spectra suggest that turbulence develops in evolved sources.

CHOICE OF CONDITIONS FOR MHD SIMULATIONS ABOVE THE ACTIVE REGION, ALLOWING THE STUDY OF THE SOLAR FLARE MECHANISM

2021 ◽  
Vol 44 ◽  
pp. 92-95
Author(s):  
A.I. Podgorny ◽  
◽  
I.M. Podgorny ◽  
A.V. Borisenko ◽  
N.S. Meshalkina ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Solar Flare ◽  
Magnetic Energy ◽  
Solar Radius ◽  
Computational Domain ◽  
Mhd Simulations ◽  
Flare Energy ◽  
Numerical Instabilities ◽  
The Magnetic Field

Primordial release of solar flare energy high in corona (at altitudes 1/40 - 1/20 of the solar radius) is explained by release of the magnetic energy of the current sheet. The observed manifestations of the flare are explained by the electrodynamical model of a solar flare proposed by I. M. Podgorny. To study the flare mechanism is necessary to perform MHD simulations above a real active region (AR). MHD simulation in the solar corona in the real scale of time can only be carried out thanks to parallel calculations using CUDA technology. Methods have been developed for stabilizing numerical instabilities that arise near the boundary of the computational domain. Methods are applicable for low viscosities in the main part of the domain, for which the flare energy is effectively accumulated near the singularities of the magnetic field. Singular lines of the magnetic field, near which the field can have a rather complex configuration, coincide or are located near the observed positions of the flare.

scholarly journals Cyclotron lines in highly magnetized neutron stars

2019 ◽  
Vol 622 ◽  
pp. A61 ◽  
Author(s):  
R. Staubert ◽  
J. Trümper ◽  
E. Kendziorra ◽  
D. Klochkov ◽  
K. Postnov ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Neutron Stars ◽  
Direct Measurement ◽  
Resonant Scattering ◽  
Electron Cyclotron ◽  
X Ray ◽  
Cyclotron Line ◽  
The Magnetic Field ◽  
Proton Cyclotron

Cyclotron lines, also called cyclotron resonant scattering features are spectral features, generally appearing in absorption, in the X-ray spectra of objects containing highly magnetized neutron stars, allowing the direct measurement of the magnetic field strength in these objects. Cyclotron features are thought to be due to resonant scattering of photons by electrons in the strong magnetic fields. The main content of this contribution focusses on electron cyclotron lines as found in accreting X-ray binary pulsars (XRBP) with magnetic fields on the order of several 1012Gauss. Also, possible proton cyclotron lines from single neutron stars with even stronger magnetic fields are briefly discussed. With regard to electron cyclotron lines, we present an updated list of XRBPs that show evidence of such absorption lines. The first such line was discovered in a 1976 balloon observation of the accreting binary pulsar Hercules X-1, it is considered to be the first direct measurement of the magnetic field of a neutron star. As of today (end 2018), we list 35 XRBPs showing evidence of one ore more electron cyclotron absorption line(s). A few have been measured only once and must be confirmed (several more objects are listed as candidates). In addition to the Tables of objects, we summarize the evidence of variability of the cyclotron line as a function of various parameters (especially pulse phase, luminosity and time), and add a discussion of the different observed phenomena and associated attempts of theoretical modeling. We also discuss our understanding of the underlying physics of accretion onto highly magnetized neutron stars. For proton cyclotron lines, we present tables with seven neutron stars and discuss their nature and the physics in these objects.

scholarly journals Mid-infrared Observations of Magnetic Fields in the Disks of Bi-Polar Outflow Sources

1997 ◽  
Vol 163 ◽  
pp. 799-800
Author(s):  
Craig H. Smith ◽  
Christopher M. Wright ◽  
David K. Aitken ◽  
Patrick F. Roche
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Configuration ◽  
Field Direction ◽  
Magnetic Field Direction ◽  
Poloidal Field ◽  
Mid Infrared ◽  
Infrared Observations ◽  
Polarization Mechanism ◽  
The Magnetic Field

AbstractWe present the results from mid-infrared spectro-polarimetric observations of a number of bi-polar outflow sources. The specto-polarimetric data provides information on the polarization mechanism and the magnetic field direction. The field direction in the disks of the observed sources is most often normal to the ambient field direction and lies in the plane of the disk, indicating a toroidal rather than poloidal field configuration.

scholarly journals Probing interstellar magnetic fields with Supernova remnants

2008 ◽  
Vol 4 (S259) ◽  
pp. 75-80 ◽  
Author(s):  
Roland Kothes ◽  
Jo-Anne Brown
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Supernova Remnants ◽  
Large Scale ◽  
Galactic Plane ◽  
Field Configuration ◽  
Large Scale Magnetic Field ◽  
Rotation Measure ◽  
Field Lines ◽  
The Magnetic Field

AbstractAs Supernova remnants expand, their shock waves are freezing in and compressing the magnetic field lines they encounter; consequently we can use Supernova remnants as magnifying glasses for their ambient magnetic fields. We will describe a simple model to determine emission, polarization, and rotation measure characteristics of adiabatically expanding Supernova remnants and how we can exploit this model to gain information about the large scale magnetic field in our Galaxy. We will give two examples: The SNR DA530, which is located high above the Galactic plane, reveals information about the magnetic field in the halo of our Galaxy. The SNR G182.4+4.3 is located close to the anti-centre of our Galaxy and reveals the most probable direction where the large-scale magnetic field is perpendicular to the line of sight. This may help to decide on the large-scale magnetic field configuration of our Galaxy. But more observations of SNRs are needed.

scholarly journals The Two Component Magnetic Field of the Galaxy

1990 ◽  
Vol 140 ◽  
pp. 54-54
Author(s):  
R.R. Andreassian ◽  
A.N. Makarov
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Configuration ◽  
Radio Sources ◽  
Magnetic Field Configuration ◽  
Spiral Arms ◽  
Two Component ◽  
The Galaxy ◽  
The Magnetic Field ◽  
Spiral Arm

The present paper is devoted to a study of the magnetic field configuration of our Galaxy based on Faraday rotation measures (RM) of 185 pulsars and 802 extragalactic radio sources. RM data of pulsars located near the plane of the Galaxy are used for the study of magnetic fields in neighbouring spiral arms. For the distribution of spiral arms the well-known model of Georgelin and Georgelin (1976) is used. The calculations show (for details see Andreassian and Makarov, 1987, 1989) that in the Perseus spiral arm and the local Orion arm the magnetic fields have approximately the same directions (lo;bo) ≈ (80°;0°), while in the Sagittarius-Carina arm the magnetic field has an opposite direction.

On the spontaneous magnetic field in a conducting liquid in turbulent motion

1950 ◽  
Vol 201 (1066) ◽  
pp. 405-416 ◽  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Energy ◽  
Turbulent Motion ◽  
Small Scale ◽  
Flow Equations ◽  
Metallic Conductor ◽  
Set Up ◽  
The Stability ◽  
The Magnetic Field

Several recent investigations in geophysics and astrophysics have involved a consideration of the hydrodynamics of a fluid which is a good electrical conductor. In this paper one of the problems which seem likely to arise in such investigations is discussed. The fluid is assumed to be incompressible and in homogeneous turbulent motion, and externally imposed electric and magnetic fields are assumed to be absent. The equations governing the interaction of the electromagnetic field and the turbulent motion are set up with the same assumptions as are used to obtain the Maxwell and current flow equations for a metallic conductor. It is shown that the equation for the magnetic field is identical in form with that for the vorticity in a non-conducting fluid; immediate deductions are that lines of magnetic force move with the fluid when the conductivity is infinite, and that the small-scale components of the turbulence have the more powerful effect on the magnetic field. The first question considered is the stability of a purely hydrodynamical system to small disturbing magnetic fields, and it is shown that the magnetic energy of the disturbance will increase provided the conductivity is greater than a critical value determined by the viscosity of the fluid. The rate of growth of magnetic energy is approximately exponential, with a doubling time which can be simply related to the properties of the turbulence. General mechanical considerations suggest that a steady state is reached when the magnetic field has as much energy as is contained in the small-scale components of the turbulence. Estimates of this amount of energy and of the region of the spectrum in which it will lie are given in terms of observable properties of the turbulence.

scholarly journals A distinct magnetic property of the inner penumbral boundary

2020 ◽  
Vol 638 ◽  
pp. A28 ◽  
Author(s):  
Jan Jurčák ◽  
Markus Schmassmann ◽  
Matthias Rempel ◽  
Nazaret Bello González ◽  
Rolf Schlichenmaier
Keyword(s):  
Magnetic Field ◽  
Magnetic Properties ◽  
Magnetic Property ◽  
Potential Field ◽  
Magnetic Energy ◽  
Vertical Component ◽  
Flux Rope ◽  
Field Configuration ◽  
The Magnetic Field ◽  
Upper Boundary

Context. Analyses of sunspot observations revealed a fundamental magnetic property of the umbral boundary: the invariance of the vertical component of the magnetic field. Aims. We analyse the magnetic properties of the umbra-penumbra boundary in simulated sunspots and thus assess their similarity to observed sunspots. We also aim to investigate the role of the plasma β and the ratio of kinetic to magnetic energy in simulated sunspots in the convective motions because these quantities cannot be reliably determined from observations. Methods. We used a set of non-gray simulation runs of sunspots with the MURaM code. The setups differed in terms of subsurface magnetic field structure and magnetic field boundary imposed at the top of the simulation domain. These data were used to synthesize the Stokes profiles, which were then degraded to the Hinode spectropolarimeter-like observations. Then, the data were treated like real Hinode observations of a sunspot, and magnetic properties at the umbral boundaries were determined. Results. Simulations with potential field extrapolation produce a realistic magnetic field configuration on the umbral boundaries of the sunspots. Two simulations with a potential field upper boundary, but different subsurface magnetic field structures, differ significantly in the extent of their penumbrae. Increasing the penumbra width by forcing more horizontal magnetic fields at the upper boundary results in magnetic properties that are not consistent with observations. This implies that the size of the penumbra is given by the subsurface structure of the magnetic field, that is, by the depth and inclination of the magnetopause, which is shaped by the expansion of the sunspot flux rope with height. None of the sunspot simulations is consistent with the observed properties of the magnetic field and the direction of the Evershed flow at the same time. Strong outward-directed Evershed flows are only found in setups with an artificially enhanced horizontal component of the magnetic field at the top boundary that are not consistent with the observed magnetic field properties at the umbra-penumbra boundary. We stress that the photospheric boundary of simulated sunspots is defined by a magnetic field strength of equipartition field value.

scholarly journals Magnetic Field Evolution in Neutron Star Crusts: Beyond the Hall Effect

Symmetry ◽  
2022 ◽  
Vol 14 (1) ◽  
pp. 130
Author(s):  
Konstantinos N. Gourgouliatos ◽  
Davide De Grandis ◽  
Andrei Igoshev
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Neutron Stars ◽  
Hall Effect ◽  
Thermal Emission ◽  
Ohmic Dissipation ◽  
Field Evolution ◽  
The Universe ◽  
The Magnetic Field ◽  
Maxwell Stresses

Neutron stars host the strongest magnetic fields that we know of in the Universe. Their magnetic fields are the main means of generating their radiation, either magnetospheric or through the crust. Moreover, the evolution of the magnetic field has been intimately related to explosive events of magnetars, which host strong magnetic fields, and their persistent thermal emission. The evolution of the magnetic field in the crusts of neutron stars has been described within the framework of the Hall effect and Ohmic dissipation. Yet, this description is limited by the fact that the Maxwell stresses exerted on the crusts of strongly magnetised neutron stars may lead to failure and temperature variations. In the former case, a failed crust does not completely fulfil the necessary conditions for the Hall effect. In the latter, the variations of temperature are strongly related to the magnetic field evolution. Finally, sharp gradients of the star’s temperature may activate battery terms and alter the magnetic field structure, especially in weakly magnetised neutron stars. In this review, we discuss the recent progress made on these effects. We argue that these phenomena are likely to provide novel insight into our understanding of neutron stars and their observable properties.

Production of monopole–antimonopole pairs in very intense but slowly varying magnetic field

2020 ◽  
Vol 35 (21) ◽  
pp. 2050116
Author(s):  
Giorgio Calucci
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Neutron Stars ◽  
Time Variation ◽  
The Magnetic Field ◽  
Astrophysical Phenomena

The production of pairs of monopole–antimonopole in presence of extremely intense magnetic fields, is briefly investigated in the case where the magnetic field undergoes also a time variation. The possibility that similar conditions are realized, with a production of ordinary particles, was already considered for astrophysical phenomena, e.g. some phases of evolution of neutron stars.

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