scholarly journals Excitation Magnetohydrodynamic Wave by Gravitational Wave Produced by Binary of Neutron Stars

2017 ◽  
Vol 45 ◽  
pp. 1760006
Author(s):  
Adam S. Gontijo ◽  
Oswaldo D. Miranda
Keyword(s):  
Magnetic Field ◽  
Neutron Stars ◽  
Gravitational Wave ◽  
Acoustic Mode ◽  
Magnetized Plasma ◽  
Uniform Field ◽  
Pressure Gradients ◽  
Magnetohydrodynamic Wave ◽  
Field Lines ◽  
The Magnetic Field

The gravitational wave, through the strongly magnetized plasma surrounding the neutron stars, in the [Formula: see text]-direction, deforms plasma particle rings in ellipses, alternating axes periodically along the direction of the magnetic field ([Formula: see text]-axis) and of the [Formula: see text]-axis. The uniform field leads to a modulation of the magnetic field, which results in magnetic pressure gradients (magneto-acoustic mode) or in the shear of the magnetic field lines (Alfvén mode). The gravitational wave drives MHD modes and transfers energy to the plasma, can become an important alternative process for the acceleration of baryons to high Lorentz factors observed in short GRBs. The total amount of energy that is transferred from the gravitational wave to the plasma is estimated ([Formula: see text]J - [Formula: see text] J), with [Formula: see text]. We compare our results with previously obtained results by other works.

Acoustic End Effects in Magnetohydrodynamic Submerged Vehicular Propulsors

1992 ◽  
Vol 36 (01) ◽  
pp. 69-76
Author(s):  
John S. Walker ◽  
Gita Talmage ◽  
Samuel H. Brown ◽  
Neal A. Sondergaard
Keyword(s):  
Magnetic Field ◽  
Inertial Force ◽  
Zero Field ◽  
Uniform Field ◽  
Field Region ◽  
Characteristic Ratio ◽  
Fringing Field ◽  
Field Lines ◽  
Channel Configuration ◽  
The Magnetic Field

This paper treats the effects near the ends of the channel on the transmission and reflection of periodic acoustic waves generated at some cross section inside a magnetohydrodynamic (MHD) seawater propulsion system. A region of high uniform magnetic field inside the MHD submerged vehicular propulsor is separated from the essentially zero magnetic field outside the channel by a nonuniform, fringing magnetic field at each end of the channel. The channel configuration chosen here is that of a straight, rectangular duct with electrically insulating top and bottom walls perpendicular to the magnetic field and highly conducting sidewalls parallel to the field. In particular, the mathematical analysis focuses on determining the percentage of the incident wave which is reflected by the fringing-field region back into the uniform-field region and the percentage which is transmitted through the fringing-field region into the zero-field region. The key parameter is the acoustic interaction parameter N, which is the characteristic ratio of the electromagnetic body force opposing motions across magnetic field lines to the inertial "force" in the acoustic wave. Solutions are presented for the fundamental, plane acoustic mode for arbitrary values of Ν and for all acoustic modes for Ν < 1. The amplitudes of the reflected and transmitted waves depend on the wave frequency, the length of the fringing-field region, N, and the type of wave mode. The magnetic field introduces a strong anisotropy with strong damping of modes involving transverse motions across magnetic field lines and with weak damping of modes involving transverse motions along field lines. This is the third in a series of articles on MHD marine propulsion from the David Taylor Research Center MHD propulsion program [Brown et al (1990), Tempelmeyer (1990)].

scholarly journals Magnetic properties of the protostellar core IRAS 15398-3359

2019 ◽  
Vol 631 ◽  
pp. A154
Author(s):  
E. Redaelli ◽  
F. O. Alves ◽  
F. P. Santos ◽  
P. Caselli
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Thermal Emission ◽  
Uniform Field ◽  
Flux Parameter ◽  
Low Mass ◽  
Gravitational Pull ◽  
Field Lines ◽  
Cold Dust ◽  
The Magnetic Field

Context. Magnetic fields can significantly affect the star formation process. The theory of the magnetically driven collapse in a uniform field predicts that the contraction initially happens along the field lines. When the gravitational pull grows strong enough, the magnetic field lines pinch inwards, giving rise to a characteristic hourglass shape. Aims. We investigate the magnetic field structure of a young Class 0 object, IRAS 15398-3359, embedded in the Lupus I cloud. Previous observations at large scales have suggested that this source evolved in an highly magnetised environment. This object thus appears to be an ideal candidate to study the magnetically driven core collapse in the low-mass regime. Methods. We performed polarisation observations of IRAS 15398-3359 at 214 μm using the SOFIA telescope, thus tracing the linearly polarised thermal emission of cold dust. Results. Our data unveil a significant bend of the magnetic field lines from the gravitational pull. The magnetic field appears ordered and aligned with the large-scale B-field of the cloud and with the outflow direction. We estimate a magnetic field strength of B = 78 μG, which is expected to be accurate within a factor of two. The measured mass-to-flux parameter is λ = 0.95, indicating that the core is in a transcritical regime.

ON THE INTERIOR OF THE NEUTRON STAR – I. NONLINEAR BEHAVIOR OF THE MAGNETIC FIELD

1994 ◽  
Vol 03 (03) ◽  
pp. 665-674
Author(s):  
RAMEN KUMAR PARUI
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Magnetic Fields ◽  
Neutron Stars ◽  
Gravitational Wave ◽  
Nonlinear Behavior ◽  
Wave Source ◽  
Strong Magnetic Fields ◽  
Outstanding Problem ◽  
The Magnetic Field

The generation of very strong magnetic fields on the surface of a neutron star has long been an outstanding problem. A spinning neutron star is considered as one of the anticipated gravitational wave sources. Here I have shown the nonlinear behavior of this magnetic field in the interior of both uncharged and charged neutron stars at equilibrium radii and obtained results favouring a gravitational wave source.

Magnetic dipole interaction with multipole magnetic field lines of neutron stars

2021 ◽  
Author(s):  
Habtamu Menberu Tedila
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Neutron Stars ◽  
Field Line ◽  
Dipole Interaction ◽  
Line Geometry ◽  
Magnetic Dipole Interaction ◽  
Field Lines ◽  
The Magnetic Field

AbstractConservation of magnetic flux is associated with regions of the powerful magnetic fields (B ∽ 1013 G) near neutron stars' surface. The vector potential generated by moving electric charge Q is uniformly distributed within a Neutron star's surface (radius R). The evolution of the magnetic field of isolated neutron stars is studied and based on magnetic flux conservation; the multipolar magnetic fields for (l = 1; l = 2; l  = 3; l  = 4) have calculated. We developed the field line equations and simulated the magnetic field line geometry for the interaction between neutron stars’ dipole–multipolar magnetic fields using the MATLAB software program.

scholarly journals Magnetic nulls in interacting dipolar fields

2021 ◽  
Vol 87 (2) ◽  
Author(s):  
Todd Elder ◽  
Allen H. Boozer
Keyword(s):  
Magnetic Field ◽  
Current Density ◽  
Magnetic Flux Tube ◽  
Electron Inertia ◽  
Characteristic Spatial Scale ◽  
Field Lines ◽  
Dipolar Fields ◽  
Time Required ◽  
Magnetic Null ◽  
The Magnetic Field

The prominence of nulls in reconnection theory is due to the expected singular current density and the indeterminacy of field lines at a magnetic null. Electron inertia changes the implications of both features. Magnetic field lines are distinguishable only when their distance of closest approach exceeds a distance $\varDelta _d$ . Electron inertia ensures $\varDelta _d\gtrsim c/\omega _{pe}$ . The lines that lie within a magnetic flux tube of radius $\varDelta _d$ at the place where the field strength $B$ is strongest are fundamentally indistinguishable. If the tube, somewhere along its length, encloses a point where $B=0$ vanishes, then distinguishable lines come no closer to the null than $\approx (a^2c/\omega _{pe})^{1/3}$ , where $a$ is a characteristic spatial scale of the magnetic field. The behaviour of the magnetic field lines in the presence of nulls is studied for a dipole embedded in a spatially constant magnetic field. In addition to the implications of distinguishability, a constraint on the current density at a null is obtained, and the time required for thin current sheets to arise is derived.

Magnetic Field Spectroheliograms from the San Fernando Observatory

1971 ◽  
Vol 43 ◽  
pp. 329-339 ◽  
Author(s):  
Dale Vrabec
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Spiral Structure ◽  
Longitudinal Component ◽  
Solar Telescope ◽  
Solar Magnetic Fields ◽  
San Fernando ◽  
Field Lines ◽  
The Magnetic Field ◽  
Field Network

Zeeman spectroheliograms of photospheric magnetic fields (longitudinal component) in the CaI 6102.7 Å line are being obtained with the new 61-cm vacuum solar telescope and spectroheliograph, using the Leighton technique. The structure of the magnetic field network appears identical to the bright photospheric network visible in the cores of many Fraunhofer lines and in CN spectroheliograms, with the exception that polarities are distinguished. This supports the evolving concept that solar magnetic fields outside of sunspots exist in small concentrations of essentially vertically oriented field, roughly clumped to form a network imbedded in the otherwise field-free photosphere. A timelapse spectroheliogram movie sequence spanning 6 hr revealed changes in the magnetic fields, including a systematic outward streaming of small magnetic knots of both polarities within annular areas surrounding several sunspots. The photospheric magnetic fields and a series of filtergrams taken at various wavelengths in the Hα profile starting in the far wing are intercompared in an effort to demonstrate that the dark strands of arch filament systems (AFS) and fibrils map magnetic field lines in the chromosphere. An example of an active region in which the magnetic fields assume a distinct spiral structure is presented.

scholarly journals Efficiency of thermal conduction in a magnetized circumgalactic medium

2021 ◽  
Vol 502 (1) ◽  
pp. 1263-1278
Author(s):  
Richard Kooij ◽  
Asger Grønnow ◽  
Filippo Fraternali
Keyword(s):  
Magnetic Field ◽  
Thermal Conduction ◽  
Large Temperature ◽  
Gas Condensation ◽  
Circumgalactic Medium ◽  
Field Lines ◽  
Gas Accretion ◽  
Cloud Evolution ◽  
The Magnetic Field ◽  
Cold Gas

ABSTRACT The large temperature difference between cold gas clouds around galaxies and the hot haloes that they are moving through suggests that thermal conduction could play an important role in the circumgalactic medium. However, thermal conduction in the presence of a magnetic field is highly anisotropic, being strongly suppressed in the direction perpendicular to the magnetic field lines. This is commonly modelled by using a simple prescription that assumes that thermal conduction is isotropic at a certain efficiency f < 1, but its precise value is largely unconstrained. We investigate the efficiency of thermal conduction by comparing the evolution of 3D hydrodynamical (HD) simulations of cold clouds moving through a hot medium, using artificially suppressed isotropic thermal conduction (with f), against 3D magnetohydrodynamical (MHD) simulations with (true) anisotropic thermal conduction. Our main diagnostic is the time evolution of the amount of cold gas in conditions representative of the lower (close to the disc) circumgalactic medium of a Milky-Way-like galaxy. We find that in almost every HD and MHD run, the amount of cold gas increases with time, indicating that hot gas condensation is an important phenomenon that can contribute to gas accretion on to galaxies. For the most realistic orientations of the magnetic field with respect to the cloud motion we find that f is in the range 0.03–0.15. Thermal conduction is thus always highly suppressed, but its effect on the cloud evolution is generally not negligible.

scholarly journals Mutual influence of magnetic field decay and thermal evolution of rotational neutron stars

2012 ◽  
Vol 8 (S291) ◽  
pp. 586-588
Author(s):  
Xia Zhou ◽  
Miao Kang ◽  
Na Wang
Keyword(s):  
Magnetic Field ◽  
Neutron Stars ◽  
Mutual Influence ◽  
Thermal Evolution ◽  
Chemical Heating ◽  
Field Decay ◽  
The Magnetic Field

AbstractThe effect of magnetic field decay on the chemical heating and thermal evolution of neutron stars is discussed. Our main goal is to study how chemical heating mechanisms and thermal evolution are changed by field decay and how magnetic field decay is modified by the thermal evolution. We show that the effect of chemical heating is suppressed by the star spin-down through decaying magnetic field at a later stage; magnetic field decay is delayed significantly relative to stars cooling without heating mechanisms; compared to typical chemical heating, the decay of the magnetic field can even cause the temperature to turn down at a later stage.

scholarly journals The development of magnetic field line wander by plasma turbulence

2017 ◽  
Vol 83 (4) ◽  
Author(s):  
Gregory G. Howes ◽  
Sofiane Bourouaine
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Magnetic Field Line ◽  
Large Scale ◽  
Magnetic Energy ◽  
Plasma Turbulence ◽  
Alfven Wave ◽  
Astrophysical Plasmas ◽  
Field Lines ◽  
The Magnetic Field

Plasma turbulence occurs ubiquitously in space and astrophysical plasmas, mediating the nonlinear transfer of energy from large-scale electromagnetic fields and plasma flows to small scales at which the energy may be ultimately converted to plasma heat. But plasma turbulence also generically leads to a tangling of the magnetic field that threads through the plasma. The resulting wander of the magnetic field lines may significantly impact a number of important physical processes, including the propagation of cosmic rays and energetic particles, confinement in magnetic fusion devices and the fundamental processes of turbulence, magnetic reconnection and particle acceleration. The various potential impacts of magnetic field line wander are reviewed in detail, and a number of important theoretical considerations are identified that may influence the development and saturation of magnetic field line wander in astrophysical plasma turbulence. The results of nonlinear gyrokinetic simulations of kinetic Alfvén wave turbulence of sub-ion length scales are evaluated to understand the development and saturation of the turbulent magnetic energy spectrum and of the magnetic field line wander. It is found that turbulent space and astrophysical plasmas are generally expected to contain a stochastic magnetic field due to the tangling of the field by strong plasma turbulence. Future work will explore how the saturated magnetic field line wander varies as a function of the amplitude of the plasma turbulence and the ratio of the thermal to magnetic pressure, known as the plasma beta.

scholarly journals Mapping of steady-state electric fields and convective drifts in geomagnetic fields – Part 1: Elementary models

2016 ◽  
Vol 34 (1) ◽  
pp. 55-65 ◽  
Author(s):  
A. D. M. Walker ◽  
G. J. Sofko
Keyword(s):  
Magnetic Field ◽  
Steady State ◽  
Electric Field ◽  
Electric Fields ◽  
Magnetic Field Line ◽  
Geomagnetic Field ◽  
Geomagnetic Field Models ◽  
Spatial Derivatives ◽  
Field Lines ◽  
The Magnetic Field

Abstract. When studying magnetospheric convection, it is often necessary to map the steady-state electric field, measured at some point on a magnetic field line, to a magnetically conjugate point in the other hemisphere, or the equatorial plane, or at the position of a satellite. Such mapping is relatively easy in a dipole field although the appropriate formulae are not easily accessible. They are derived and reviewed here with some examples. It is not possible to derive such formulae in more realistic geomagnetic field models. A new method is described in this paper for accurate mapping of electric fields along field lines, which can be used for any field model in which the magnetic field and its spatial derivatives can be computed. From the spatial derivatives of the magnetic field three first order differential equations are derived for the components of the normalized element of separation of two closely spaced field lines. These can be integrated along with the magnetic field tracing equations and Faraday's law used to obtain the electric field as a function of distance measured along the magnetic field line. The method is tested in a simple model consisting of a dipole field plus a magnetotail model. The method is shown to be accurate, convenient, and suitable for use with more realistic geomagnetic field models.

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