scholarly journals Evolution of magnetic deformation in neutron star crust

2020 ◽  
Author(s):  
Yasufumi Kojima ◽  
Shota Kisaka ◽  
Kotaro Fujisawa
Keyword(s):  
Neutron Star ◽  
Elastic Limit ◽  
Magnetic Energy ◽  
Fluid Velocity ◽  
Ohmic Dissipation ◽  
Bulk Fluid ◽  
Neutron Star Crust ◽  
Dipole Component ◽  
Prolate Shape ◽  
The Magnetic Field

Abstract In this study, we examine the magnetic field evolution occurring in a neutron star crust. Beyond the elastic limit, the lattice ions are assumed to act as a plastic flow. The Ohmic dissipation, Hall drift, and bulk fluid velocity driven by the Lorentz force are considered in our numerical simulation. A magnetically induced quadrupole deformation is observed in the crust during the evolution. Generally, the ellipticity decreases as the magnetic energy decreases. In a toroidal-field-dominated model, the sign of the ellipticity changes. Namely, the initial prolate shape tends to become oblate. This occurs because the toroidal component decays rapidly on a smaller timescale than the poloidal dipole component. We find that the magnetic dipole component does not change significantly on the Hall timescale of ∼1Myr for the considered simple initial models. Thus, a more complex initial model is required to study the fast decay of surface dipoles on the abovementioned timescale.

scholarly journals Magnetic-field evolution with large-scale velocity circulation in a neutron-star crust

2020 ◽  
Vol 494 (3) ◽  
pp. 3790-3798 ◽  
Author(s):  
Yasufumi Kojima ◽  
Kazuki Suzuki
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Lorentz Force ◽  
Large Scale ◽  
Magnetic Energy ◽  
Fluid Motion ◽  
Navier Stokes Equation ◽  
Ohmic Dissipation ◽  
Neutron Star Crust ◽  
Field Evolution

ABSTRACT We examine the effects of plastic flow that appear in a neutron-star crust when a magnetic stress exceeds the threshold. The dynamics involved are described using the Navier–Stokes equation comprising the viscous-flow term, and the velocity fields for the global circulation are determined using quasi-stationary approximation. We simulate the magnetic-field evolution by taking into consideration the Hall drift, Ohmic dissipation, and fluid motion induced by the Lorentz force. The decrease in the magnetic energy is enhanced, as the energy converts to the bulk motion energy and heat. It is found that the bulk velocity induced by the Lorentz force has a significant influence in the low-viscosity and strong-magnetic-field regimes. This effect is crucial near magnetar surfaces.

scholarly journals Estimation of Electrical Conductivity and Magnetization Parameter of Neutron Star Crusts and Applied to the High-Braking-Index Pulsar PSR J1640-4631

Universe ◽  
2020 ◽  
Vol 6 (5) ◽  
pp. 63
Author(s):  
Hui Wang ◽  
Zhi-Fu Gao ◽  
Huan-Yu Jia ◽  
Na Wang ◽  
Xiang-Dong Li
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Neutron Stars ◽  
General Expression ◽  
Equations Of State ◽  
Rotation Period ◽  
Ohmic Dissipation ◽  
Hartree Fock ◽  
Induction Equation ◽  
The Magnetic Field

Young pulsars are thought to be highly magnetized neutron stars (NSs). The crustal magnetic field of a NS usually decays at different timescales in the forms of Hall drift and Ohmic dissipation. The magnetization parameter ω B τ is defined as the ratio of the Ohmic timescale τ O h m to the Hall drift timescale τ H a l l . During the first several million years, the inner temperature of the newly born neutron star cools from T = 10 9 K to T = 1.0 × 10 8 K, and the crustal conductivity increases by three orders of magnitude. In this work, we adopt a unified equations of state for cold non-accreting neutron stars with the Hartree–Fock–Bogoliubov method, developed by Pearson et al. (2018), and choose two fiducial dipole magnetic fields of B = 1.0 × 10 13 G and B = 1.0 × 10 14 G, four different temperatures, T, and two different impurity concentration parameters, Q, and then calculate the conductivity of the inner crust of NSs and give a general expression of magnetization parameter for young pulsars: ω B τ ≃ ( 1 − 50 ) B 0 / ( 10 13 G) by using numerical simulations. It was found when B ≤ 10 15 G, due to the quantum effects, the conductivity increases slightly with the increase in the magnetic field, the enhanced magnetic field has a small effect on the matter in the low-density regions of the crust, and almost has no influence the matter in the high-density regions. Then, we apply the general expression of the magnetization parameter to the high braking-index pulsar PSR J1640-4631. By combining the observed arrival time parameters of PSR J1640-4631 with the magnetic induction equation, we estimated the initial rotation period P 0 , the initial dipole magnetic field B 0 , the Ohm dissipation timescale τ O h m and Hall drift timescale τ H a l l . We model the magnetic field evolution and the braking-index evolution of the pulsar and compare the results with its observations. It is expected that the results of this paper can be applied to more young pulsars.

scholarly journals Fallback Disks, Magnetars and Other Neutron Stars

2012 ◽  
Vol 8 (S290) ◽  
pp. 93-100 ◽  
Author(s):  
M. Ali Alpar ◽  
Ş. Çalışkan ◽  
Ü. Ertan
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Neutron Stars ◽  
Initial Conditions ◽  
Disk Model ◽  
Dipole Component ◽  
Salient Points ◽  
Period Derivative ◽  
The Magnetic Field ◽  
Broad Overview

AbstractThe presence of matter with angular momentum, in the form of a fallback disk around a young isolated neutron star will determine its evolution. This leads to an understanding of many properties of different classes of young neutron stars, in particular a natural explanation for the period clustering of AXPs, SGRs and XDINs. The spindown or spinup properties of a neutron star are determined by the dipole component of the magnetic field. The natural possibility that magnetars and other neutron stars may have different strengths of the dipole and higher multipole components of the magnetic field is now actually required by observations on the spindown rates of some magnetars. This talk gives a broad overview and some applications of the fallback disk model to particular neutron stars. Salient points are: (i) A fallback disk has already been observed around the AXP 4U 0142+61 some years ago. (ii) The low observed spindown rate of the SGR 0418+5729 provides direct evidence that the dipole component of the field is in the 1012G range. All properties of the SGR 0418+5729 at its present age can be explained by spindown under torques from a fallback disk. (iii) The anomalous braking index of PSR J1734-3333 can also be explained by the fallback disk model which gives the luminosity, period, period derivative and the period second derivative at the present age. (iv) These and all applications to a variety of other sources employ the same disk physics and evolution, differing only in the initial conditions of the disk.

scholarly journals Non-Stationary Accretion in Her X–1–like Systems

1996 ◽  
Vol 160 ◽  
pp. 537-538
Author(s):  
U. Geppert ◽  
V. Urpin
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Total Mass ◽  
Binary Systems ◽  
High Mass ◽  
Neutron Star Crust ◽  
Solid Region ◽  
Low Mass ◽  
Field Decay ◽  
The Magnetic Field

Accretion heats the neutron star crust thereby decreasing the electric conductivity in the solid region. This leads to a rapid field decay when the currents supporting the field are concentrated in the solid crust (Geppert & Urpin 1994, Urpin & Geppert 1995). Depending on the duration of the accretion phase and on the total mass accreted the field can be decreased by 3 − 4 orders of magnitude after 106− 107years. This mechanism explains the low magnetic fields of many pulsars entering binary systems.However, there exist both low–mass (e.g. Her X–1, 4U 1626–67) and high–mass (e.g. Cen X–3, SMC X–1) systems, where the neutron star deserves strong accretion and the magnetic field is still large.

Kinematic dynamos and the Earth’s magnetic field

1973 ◽  
Vol 275 (1251) ◽  
pp. 425-461 ◽  
Keyword(s):  
Magnetic Field ◽  
Inner Core ◽  
Magnetic Energy ◽  
Liquid Core ◽  
Outer Part ◽  
Ohmic Dissipation ◽  
Tidal Dissipation ◽  
Magnetic Dipoles ◽  
Magnetic Energy Density ◽  
The Magnetic Field

The Bullard—Gellman formalism is applied to investigate the existence of convergent solutions for steady kinematic dynamos. It is found that the solutions for the Bullard—Gellman dynamo, as well as for Lilley’s modification of it, do not converge. Convergent solutions have been found for a class of spherical convective cells which would be stationary in a perfect fluid in the absence of rotation and of the magnetic field. By calibrating the theoretical magnetic dipole so as to fit the observed value at the Earth’s surface, one can find a dynamo in the above class which also matches the observed equatorial magnetic dipoles. There is a dynamo which has a rate of total ohmic dissipation of only 1.8 x 1016 erg s-1 for an assumed electrical conductivity of 3 x 10~6 e.m.u.'f This is one thousandth the rate of tidal dissipation, and one hundred thousandth the rate of heat outflow from the surface of the Earth. The required velocities are of the order of 10~3 cm s_1, and the average magnetic energy density is 4 erg cm-3. The internal structure of the magnetic field in this model shows a dynamo mechanism situated in the outer part of the liquid core and is thus insensitive to possible rigidity of the material in the * inner core.

scholarly journals Accretion and magnetic field submergence in neutron star surface

2008 ◽  
Vol 4 (S259) ◽  
pp. 135-136
Author(s):  
C. Giovanny Bernal ◽  
Dany Page ◽  
William H. Lee
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Neutron Star Crust ◽  
Star Surface ◽  
The Magnetic Field

AbstractWe study the effects of hypercritical accretion onto a neutron star surface. The magnetic field submergence in the neutron star crust and the possible rediffusion is investigated.

scholarly journals Effect of magnetic field on the burning of a neutron star

2018 ◽  
Vol 27 (10) ◽  
pp. 1850083 ◽  
Author(s):  
Ritam Mallick ◽  
Amit Singh
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Initial Density ◽  
Considerable Effect ◽  
Magnetic Axis ◽  
Small Window ◽  
Exothermic Process ◽  
Text Density ◽  
The Magnetic Field ◽  
Observational Aspect

In this paper, we present the effect of a strong magnetic field in the burning of a neutron star (NS). We have used relativistic magneto-hydrostatic (MHS) conservation equations for studying the PT from nuclear matter (NM) to quark matter (QM). We found that the shock-induced phase transition (PT) is likely if the density of the star core is more than three times nuclear saturation ([Formula: see text]) density. The conversion process from NS to quark star (QS) is found to be an exothermic process beyond such densities. The burning process at the star center most likely starts as a deflagration process. However, there can be a small window at lower densities where the process can be a detonation one. At small enough infalling matter velocities the resultant magnetic field of the QS is lower than that of the NS. However, for a higher value of infalling matter velocities, the magnetic field of QM becomes larger. Therefore, depending on the initial density fluctuation and on whether the PT is a violent one or not the QS could be more magnetic or less magnetic. The PT also have a considerable effect on the tilt of the magnetic axis of the star. For smaller velocities and densities the magnetic angle are not affected much but for higher infalling velocities tilt of the magnetic axis changes suddenly. The magnetic field strength and the change in the tilt axis can have a significant effect on the observational aspect of the magnetars.

Turbulent dynamo action at low magnetic Reynolds number

1970 ◽  
Vol 41 (2) ◽  
pp. 435-452 ◽  
Author(s):  
H. K. Moffatt
Keyword(s):  
Magnetic Field ◽  
Reynolds Number ◽  
Large Scale ◽  
Isotropic Turbulence ◽  
Magnetic Energy ◽  
Magnetic Reynolds Number ◽  
Dynamo Action ◽  
Ohmic Dissipation ◽  
Magnetic Energy Density ◽  
Magnetic Diffusivity

The effect of turbulence on a magnetic field whose length-scale L is initially large compared with the scale l of the turbulence is considered. There are no external sources for the field, and in the absence of turbulence it decays by ohmic dissipation. It is assumed that the magnetic Reynolds number Rm = u0l/λ (where u0 is the root-mean-square velocity and λ the magnetic diffusivity) is small. It is shown that to lowest order in the small quantities l/L and Rm, isotropic turbulence has no effect on the large-scale field; but that turbulence that lacks reflexional symmetry is capable of amplifying Fourier components of the field on length scales of order Rm−2l and greater. In the case of turbulence whose statistical properties are invariant under rotation of the axes of reference, but not under reflexions in a point, it is shown that the magnetic energy density of a magnetic field which is initially a homogeneous random function of position with a particularly simple spectrum ultimately increases as t−½exp (α2t/2λ3) where α(= O(u02l)) is a certain linear functional of the spectrum tensor of the turbulence. An analogous result is obtained for an initially localized field.

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.

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