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

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.

Ohmic and viscous dissipation effects on micropolar non-Newtonian nanofluid Al2O3 flow through a non-Darcy porous media

Inclined uniform magnetic field and mixed convention effects on micropolar non-Newtonian nanofluid Al2O3 flow with heat transfer are studied. The heat source, both viscous and ohmic dissipation and temperature micropolarity properties are considered. We transformed our system of non-linear partial differential equations into ordinary equations by using suitable similarity transformations. These equations are solved by making use of Rung–Kutta–Merson method in a shooting and matching technique. The numerical solutions of the tangential velocity, microtation velocity, temperature and nanoparticle concentration are obtained as functions of the physical parameters of the problem. Moreover, we discussed the effects of these parameters on the numerical solutions and depicted graphically. It is obvious that these parameters control the fluid flow. It is noticed that the tangential velocity magnifies with an increase in the value of Darcy number. Meanwhile, the value of the tangential velocity reduces with the elevation in the value of the magnetic field parameter. On the other hand, the elevation in the value of Brownian motion parameter leads to a reduction in the value of fluid temperature. Furthermore, increasing in the value of heat source parameter makes an enhancement in the value of nanoparticles concentration. The current study has many accomplishments in several scientific areas like medical industry, medicine, and others. Therefore, it represents the depiction of gas or liquid motion over a surface. When particles are moving from areas of high concentration to areas of low concentration.

A novel approach for EMHD Williamson nanofluid over nonlinear sheet with double stratification and Ohmic dissipation

The current article highlights the non-Newtonian Williamson nanofluid with electro-magnetohydrodynamic (EMHD) flow over a nonlinear expanding sheet. Thermal and solutal stratification effects are considered due to the higher temperature difference and the impact of variable viscosity along with Ohmic dissipation is also incorporated. Transformation is applied for the conversion of physical partial differential equations (PDEs) into non-dimensional higher order nonlinear ordinary differential equations (ODEs). A well-known analytical approach known as the homotopy analysis method (HAM) is effectively applied to solve the differential equations. Different non-dimensional emerging parameters such as Weissenberg and Hartman number, Brownian motion and stratification parameters, stretching index, viscosity parameter, and Lewis number are used to check their impacts on velocity, concentration, and temperature profiles. To acquire the optimal solution through HAM, [Formula: see text] -curves are drawn. In the tabulated form, the numerical values for the non-dimensional Nusselt number and skin friction are arranged.

Internal-current Lorentz-force Heating of Astrophysical Objects

Two forms of ohmic heating of astrophysical secondaries have received particular attention: unipolar-generator heating with currents running between the primary and secondary, and magnetic induction heating due to the primary’s time-varying field. Neither appears to cause significant dissipation in the contemporary solar system. But these discussions have overlooked heating derived from the spatial variation of the primary’s field across the interior of the secondary. This leads to Lorentz-force-driven currents around paths entirely internal to the secondary, with resulting ohmic heating. We examine three ways to drive such currents, by the cross product of (1) the secondary’s azimuthal orbital velocity with the nonaxially symmetric field of the primary, (2) the radial velocity (due to nonzero eccentricity) of the secondary with the primary’s field, or (3) the out-of-plane velocity (due to nonzero inclination) with the primary’s field. The first of these operates even for a spin-locked secondary whose orbit has zero eccentricity, in strong contrast to tidal dissipation. We show that Jupiter’s moon Io today could dissipate about 600 GW (more than likely current radiogenic heating) in the outer 100 m of its metallic core by this mechanism. Had Io ever been at 3 Jovian radii instead of its current 5.9, it could have been dissipating 15,000 GW. Ohmic dissipation provides a mechanism that could operate in any solar system to drive inward migration of secondaries that then necessarily comes to a halt upon reaching a sufficiently close distance to the primary.

Exploring extreme magnetization phenomena in directly-driven imploding cylindrical targets

This paper uses extended-magnetohydrodynamics (MHD) simulations to explore an extreme magnetized plasma regime realisable by cylindrical implosions on the OMEGA laser facility. This regime is characterized by highly compressed magnetic fields (greater than 10kT across the fuel), which contain a significant proportion of the implosion energy and induce large electrical currents in the plasma. Parameters governing the different magnetization processes such as Ohmic dissipation and suppression of instabilities by magnetic tension are presented, allowing for optimization of experiments to study specific phenomena. For instance, a dopant added to the target gas-fill can enhance magnetic flux compression while enabling spectroscopic diagnosis of the imploding core. In particular, the use of Ar K-shell spectroscopy is investigated by performing detailed non-LTE atomic kinetics and radiative transfer calculations on the MHD data. Direct measurement of the core electron density and temperature would be possible, allowing for both the impact of magnetization on the final temperature and thermal pressure to be obtained. By assuming the magnetic field is frozen into the plasma motion, which is shown to be a good approximation for highly magnetized implosions, spectroscopic diagnosis could be used to estimate which magnetization processes are ruling the implosion dynamics; for example, a relation is given for inferring whether thermally-driven or current-driven transport is dominating.

Universal Protoplanetary Disk Size under Complete Nonideal Magnetohydrodynamics: The Interplay between Ion-neutral Friction, Hall Effect, and Ohmic Dissipation

The role of nonideal magnetohydrodynamics has been proven critical during the formation of protoplanetary disks, particularly in regulating their sizes. We provide a simple model to predict the disk size under the interplay among ambipolar diffusion, the Hall effect, and ohmic dissipation. The model predicts a small disk size of around 20 au that depends only sublinearly on disk parameters, for a wide range of initial conditions of subsolar mass and moderate magnetization. It is able to explain phenomena manifested in existing numerical simulations, including the bimodal disk behavior under parallel and antiparallel alignment between the rotation and magnetic field. In the parallel configuration, the disk size decreases and eventually disappears. In the antiparallel configuration, the disk has an outer partition (or pseudodisk), which is flat, shrinking, and short-lived, as well as an inner partition, which grows slowly with mass and is long-lived. Even with significant initial magnetization, the vertical field in the disk can only dominate at the early stage when the mass is low, and the toroidal field eventually dominates in all disks.

Numerical Simulations of Magnetic Dipole over a Nonlinear Radiative Eyring–Powell Nanofluid considering Viscous and Ohmic Dissipation Effects

This research work interprets the influences of magnetic dipole over a radiative Eyring–Powell fluid flow past a stretching sheet while considering the impacts of viscous and ohmic dissipation that produce a quite illustrious effect due to the generated magnetic dipole. This whole analysis is characterized by the effects of steady, laminar, and incompressible flow. The highly nonlinear and coupled partial differential equations (PDEs) are remodeled into a system of nonlinear ordinary differential equations (ODEs) by utilizing reliable and nondimensional parameters leading to the momentum, thermal, and concentration equations, that are computationally solved using b v p 4 c on MATLAB, and “dsolve” command on MAPLE software, in the companionship of boundary conditions. The physical constraints such as viscous and ohmic dissipation and many other sundry parametric effects are sketched with their ultimate effects on fluid flow. For the sustenance of this research with the prior work and in collaboration with the below mentioned literature review, a comprehensive differentiation is given, which defines the sustainability of the current work. The Buongiorno nanoliquid model elaborates the thermophoresis and Brownian features that are deliberately scrutinized within the influence of activation energy. Also, the skin friction coefficient, Nusselt number, and Sherwood number are illustrated in tables. The skin friction coefficient decreases with a rise in the ferromagnetic interaction parameter as well as the Hartmann number, whereas the Nusselt number and Sherwood number show variation for varying parameters. It can be observed that Eyring–Powell fluid intensifies the rate of heat and mass transfer.

Homotopy perturbation approach for Ohmic dissipation and mixed convection effects on non-Newtonian nanofluid flow between two co-axial tubes with peristalsis

In this study, the effects of radially varying magnetic field, internal heat generation and mixed convection with thermal radiation on peristaltic motion of a non-Newtonian fluid are investigated. The fluid used is third-grade model. The flow is through the gap between two co-axial vertical tubes under the effect of radially varying magnetic field. The outer tube is flexible with sinusoidal deformations. The problem is modulated mathematically by a system of partial differential equations which describes the equations of momentum, heat transfer and nanoparticles concentration which are simplified by using long wave length and low-Reynolds number assumptions. The closed solutions of fluid temperature and nanoparticle concentration are obtained, and the solution of velocity is obtained by using the homotopy perturbation method (HPM). The radially varying magnetic field effect on the axial velocity is discussed and it is shown that the increase of magnetic field parameter tends to reduce the fluid flow.

Pulsating flow of electrically conducting couple stress nanofluid in a channel with ohmic dissipation and thermal radiation – Dynamics of blood

The present work discloses the magnetohydrodynamic pulsating flow of blood-carrying nanoparticles in a channel with the viscous dissipation and Joule heating effects. Couple stress fluid is treated as blood which is the base fluid. The Maxwell Garnett model for thermal conductivity of nanofluid is considered. The thermal radiation and heat source/sink impacts are taken into account. Analytical expressions for dimensionless flow variables are obtained by employing the perturbation method. The impact of active parameters on flow variables is graphically presented. The obtained results show that the velocity of nanofluid increases with an increment in frequency parameter, whereas it decreases for a rise in Hartmann number, nanoparticles volume fraction and couple stress parameter. There is an enhancement in temperature of nanofluid with increasing viscous dissipation, whereas there is a decrease in temperature with an increase in the applied magnetic field. The Nusselt number rises with an enhancement in volume fraction of nanoparticles and Hartmann number at both the walls. Further, the validity of present results is assured by the comparison of analytical and numerical outcomes with an excellent harmony.