scholarly journals Rotating Melvin-like Universes and Wormholes in General Relativity

Symmetry ◽  
2020 ◽  
Vol 12 (8) ◽  
pp. 1306
Author(s):  
Kirill Bronnikov ◽  
Vladimir Krechet ◽  
Vadim Oshurko
Keyword(s):  
Magnetic Field ◽  
General Relativity ◽  
Equation Of State ◽  
Symmetry Axis ◽  
Energy Condition ◽  
Flat Space ◽  
Stiff Matter ◽  
Cylindrically Symmetric ◽  
The One ◽  
The Magnetic Field

We find a family of exact solutions to the Einstein–Maxwell equations for rotating cylindrically symmetric distributions of a perfect fluid with the equation of state p=wρ (|w|<1), carrying a circular electric current in the angular direction. This current creates a magnetic field along the z axis. Some of the solutions describe geometries resembling that of Melvin’s static magnetic universe and contain a regular symmetry axis, while some others (in the case w>0) describe traversable wormhole geometries which do not contain a symmetry axis. Unlike Melvin’s solution, those with rotation and a magnetic field cannot be vacuum and require a current. The wormhole solutions admit matching with flat-space regions on both sides of the throat, thus forming a cylindrical wormhole configuration potentially visible for distant observers residing in flat or weakly curved parts of space. The thin shells, located at junctions between the inner (wormhole) and outer (flat) regions, consist of matter satisfying the Weak Energy Condition under a proper choice of the free parameters of the model, which thus forms new examples of phantom-free wormhole models in general relativity. In the limit w→1, the magnetic field tends to zero, and the wormhole model tends to the one obtained previously, where the source of gravity is stiff matter with the equation of state p=ρ.

scholarly journals Equation of State of a Magnetized Dense Neutron System

Universe ◽  
2019 ◽  
Vol 5 (5) ◽  
pp. 104 ◽  
Author(s):  
Efrain J. Ferrer ◽  
Aric Hackebill
Keyword(s):  
Magnetic Field ◽  
Equation Of State ◽  
Chemical Potential ◽  
Compact Objects ◽  
Field Direction ◽  
Neutron Density ◽  
Magnetic Field Direction ◽  
System Equation ◽  
The One ◽  
The Magnetic Field

We discuss how a magnetic field can affect the equation of state of a many-particle neutron system. We show that, due to the anisotropy in the pressures, the pressure transverse to the magnetic field direction increases with the magnetic field, while the one along the field direction decreases. We also show that in this medium there exists a significant negative field-dependent contribution associated with the vacuum pressure. This negative pressure demands a neutron density sufficiently high (corresponding to a baryonic chemical potential of μ = 2.25 GeV) to produce the necessary positive matter pressure that can compensate for the gravitational pull. The decrease of the parallel pressure with the field limits the maximum magnetic field to a value of the order of 10 18 G, where the pressure decays to zero. We show that the combination of all these effects produces an insignificant variation of the system equation of state. We also found that this neutron system exhibits paramagnetic behavior expressed by the Curie’s law in the high-temperature regime. The reported results may be of interest for the astrophysics of compact objects such as magnetars, which are endowed with substantial magnetic fields.

scholarly journals Vorticity of a Perfect Fluid Undergoing a Gravitational Collapse

1976 ◽  
Vol 29 (5) ◽  
pp. 413 ◽  
Author(s):  
DP Mason
Keyword(s):  
Magnetic Field ◽  
General Relativity ◽  
Equation Of State ◽  
Energy Density ◽  
Perfect Fluid ◽  
Gravitational Collapse ◽  
Propagation Equation ◽  
Spatial Geometry ◽  
Relativistic Magnetohydrodynamics ◽  
The Magnetic Field

The vorticity propagation equation for a perfect fluid in general relativity is derived in a form which is the same as that of Maxwell's equation for the magnetic field four-vector in relativistic magnetohydrodynamics. Starting from this result, an expression for the change of vorticity during a gravitational collapse is obtained in terms of the spatial geometry, using a procedure similar to that introduced by Cocke (1966) in relativistic magnetohydrodynamics. It is assumed that the equation of state of the fluid is p = 1Xp" where IX is a constant and p, is the total proper energy density. If t < IX :s;; 1, it is found that the vorticity tends to zero during an isotropic collapse, in agreement with a result obtained previously by Ellis (1973) using a different procedure. Nonisotropic collapses are also considered. The dynamical importance of vorticity in a gravitational collapse is examined by considering the behaviour of w2 /p,.

scholarly journals Neutron anomalous magnetic moment in dense magnetized systems

2018 ◽  
Vol 27 (02) ◽  
pp. 1850011
Author(s):  
Zeinab Rezaei
Keyword(s):  
Magnetic Field ◽  
Equation Of State ◽  
Magnetic Moment ◽  
Anomalous Magnetic Moment ◽  
Nuclear Potential ◽  
Order Constraint ◽  
The Magnetic Field

In this work, we calculate the neutron anomalous magnetic moment (AMM) supposing that this value can depend on the density and magnetic field of the system. We employ the lowest-order constraint variation (LOCV) method and [Formula: see text] nuclear potential to calculate the medium dependency of the neutron AMM. It is confirmed that the neutron AMM increases by increasing the density, while it decreases as the magnetic field grows. The energy and equation of state for the system have also been investigated.

The Culgoora Magnetograph

1971 ◽  
Vol 43 ◽  
pp. 24-29 ◽  
Author(s):  
J. V. Ramsay ◽  
R. G. Giovanelli ◽  
H. R. Gillett
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Angular Resolution ◽  
Field Of View ◽  
Large Field ◽  
Sensitive Line ◽  
The One ◽  
The Magnetic Field

The magnetograph is based on a high-resolution filter which serves in place of a spectrograph, except that a reasonably large field of view (one-quarter of the Sun's diameter) can be observed at the one instant. Observations are made by obtaining filtergrams of opposite circular polarizations simultaneously in the wing of a magnetically sensitive line. Exposure times are about 0.3 s, the angular resolution of the magnetic field is about 2 arc s, closest frame repetition rates about 8 s. The filtergrams are processed subsequently by photographic or television subtraction. Semiautomatic photographic and/or TV subtractions yield magnetograms suitable for cinematographic projection though the subtractions are not yet as perfect as those obtained by individual subtraction.

scholarly journals On the Predictive Power of the Minimum Energy Condition

1993 ◽  
Vol 157 ◽  
pp. 413-414
Author(s):  
Martin Pohl
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Predictive Power ◽  
Spiral Galaxies ◽  
Minimum Energy ◽  
Energy Condition ◽  
Cosmic Ray ◽  
Γ Ray ◽  
Minimum Energy Method ◽  
The Magnetic Field

We reexamine the minimum energy method to determine the magnetic field strength in spiral galaxies from the cosmic ray standpoint of view. It is shown that for example in M51 the estimated field strength is about a factor of 2 lower than obtained with the standard method. As a by-product the corresponding γ-ray flux from the galaxies can be calculated, which will allow further improvement of the method provided reliable γ-ray spectra are at hand.

Travelling fronts in nonlocal models for phase separation in an external field

1997 ◽  
Vol 127 (4) ◽  
pp. 823-835 ◽  
Author(s):  
Enza Orlandi ◽  
Livio Triolo
Keyword(s):  
Magnetic Field ◽  
Metastable Phase ◽  
Glauber Dynamics ◽  
One Dimensional ◽  
Kac Potentials ◽  
Nonlocal Models ◽  
Nonlocal Evolution Equation ◽  
Travelling Fronts ◽  
The One ◽  
The Magnetic Field

We consider the one-dimensional, nonlocal, evolution equation derived by De Masi et al. (1995) for Ising systems with Glauber dynamics, Kac potentials and magnetic field. We prove the existence of travelling fronts, their uniqueness modulo translations among the monotone profiles and their linear stability for all the admissible values of the magnetic field for which the underlying spin system exhibits a stable and metastable phase.

scholarly journals VII. Experimental researches in electricity.-Twenty-third Series

1850 ◽  
Vol 140 ◽  
pp. 171-188 ◽  
Keyword(s):  
Magnetic Field ◽  
Mode Of Action ◽  
Royal Society ◽  
The Other ◽  
Experimental Proof ◽  
Philosophical Paper ◽  
Iron Nickel ◽  
The One ◽  
Experimental Researches ◽  
The Magnetic Field

Four years ago I suggested that all the phenomena presented by diamagnetic bodies, when subjected to the forces in the magnetic field, might be accounted for by assuming that they then possessed a polarity the same in kind as, but the reverse in direction of, that acquired by iron, nickel and ordinary magnetic bodies under the same circumstances (2429. 2430.). This view was received so favourably by Plücker, Reich and others, and above all by W. Weber, that I had great hopes it would be confirmed; and though certain experiments of my own (2497.) did not increase that hope, still my desire and expectation were in that direction. Whether bismuth, copper, phosphorus, &c., when in the magnetic field, are polar or not, is however an exceedingly important question; and very essential and great differences, in the mode of action of these bodies under the one view or the other, must be conceived to exist. I found that in every endeavour to proceed by induction of experiment from that which is known in this department of science to the unknown, so much uncertainty, hesitation and discomfort arose from the unsettled state of my mind on this point, that I determined, if possible, to arrive at some experimental proof either one way or the other. This was the more needful, because of the conclusion in the affirmative to which Weber had come in his very philosophical paper; and so important do I think it for the progress of science, that, in those imperfectly developed regions of knowledge, which form its boundaries, our conclusions and deductions should not go far beyond, or at all events not aside from the results of experiment (except as suppositions), that I do not hesitate to lay my present labours, though they arrive at a negative result, before the Royal Society.

A TOY MODEL FOR SCALARS IN TRANSIENT MAGNETIC FIELDS

2011 ◽  
Vol 26 (17) ◽  
pp. 1245-1255 ◽  
Author(s):  
CIPRIAN DARIESCU ◽  
MARINA-AURA DARIESCU
Keyword(s):  
Magnetic Field ◽  
Gordon Equation ◽  
Wave Number ◽  
Amplitude Function ◽  
Charged Boson ◽  
Klein Gordon ◽  
The One ◽  
Transient Magnetic Fields ◽  
Interaction Contribution ◽  
The Magnetic Field

We consider a special magnetic field, as for example the one in the crust of a magnetar, and solve the Klein–Gordon equation describing scalars evolving in such a configuration. For the wave number inside some computable ranges, the amplitude function of the charged boson is very sensitive to the magnetic field induction, turning from oscillatory to exponentially growing modes along Oz. One can recover the periodic behavior characterized by stationary amplitudes, by adding a self-interaction contribution to the spontaneously broken Lagrangian.

scholarly journals On dynamo action in the giant star Pollux: first results

2013 ◽  
Vol 9 (S302) ◽  
pp. 363-364 ◽  
Author(s):  
Ana Palacios ◽  
Allan Sacha Brun
Keyword(s):  
Magnetic Field ◽  
Magnetic Field Intensity ◽  
Rotation Period ◽  
Dynamo Action ◽  
Convective Envelope ◽  
Giant Star ◽  
First Results ◽  
The One ◽  
3D Mhd Simulation ◽  
The Magnetic Field

AbstractWe present preliminary results of a 3D MHD simulation of the convective envelope of the giant star Pollux for which the rotation period and the magnetic field intensity have been measured from spectroscopic and spectropolarimetric observations. This giant is one of the first single giants with a detected magnetic field, and the one with the weakest field so far. Our aim is to understand the development and the action of the dynamo in its extended convective envelope.

The self-similar, non-linear evolution of rotating magnetic flux ropes

1995 ◽  
Vol 13 (8) ◽  
pp. 815-827 ◽  
Author(s):  
C. J. Farrugia ◽  
V. A Osherovich ◽  
L. F. Burlaga
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Small Amplitude ◽  
Symmetry Axis ◽  
Flux Rope ◽  
Magnetic Clouds ◽  
Linear Evolution ◽  
Multiplicative Factor ◽  
Self Similar ◽  
The Magnetic Field

Abstract. We study, in the ideal MHD approximation, the non-linear evolution of cylindrical magnetic flux tubes differentially rotating about their symmetry axis. Our force balance consists of inertial terms, which include the centrifugal force, the gradient of the axial magnetic pressure, the magnetic pinch force and the gradient of the gas pressure. We employ the "separable" class of self-similar magnetic fields, defined recently. Taking the gas to be a polytrope, we reduce the problem to a single, ordinary differential equation for the evolution function. In general, two regimes of evolution are possible; expansion and oscillation. We investigate the specific effect rotation has on these two modes of evolution. We focus on critical values of the flux rope parameters and show that rotation can suppress the oscillatory mode. We estimate the critical value of the angular velocity Ωcrit, above which the magnetic flux rope always expands, regardless of the value of the initial energy. Studying small-amplitude oscillations of the rope, we find that torsional oscillations are superimposed on the rotation and that they have a frequency equal to that of the radial oscillations. By setting the axial component of the magnetic field to zero, we study small-amplitude oscillations of a rigidly rotating pinch. We find that the frequency of oscillation ω is inversely proportional to the angular velocity of rotation Ω; the product ωΩbeing proportional to the inverse square of the Alfvén time. The period of large-amplitude oscillations of a rotating flux rope of low beta increases exponentially with the energy of the equivalent 1D oscillator. With respect to large-amplitude oscillations of a non-rotating flux rope, the only change brought about by rotation is to introduce a multiplicative factor greater than unity, which further increases the period. This multiplicative factor depends on the ratio of the azimuthal speed to the Alfvén speed. Finally, considering interplanetary magnetic clouds as cylindrical flux ropes, we inquire whether they rotate. We find that at 1 AU only a minority do. We discuss data on two magnetic clouds where we interpret the presence in each of vortical plasma motion about the symmetry axis as a sign of rotation. Our estimates for the angular velocities suggest that the parameters of the two magnetic clouds are below critical values. The two clouds differ in many respects (such as age, bulk flow speed, size, handedness of the magnetic field, etc.), and we find that their rotational parameters reflect some of these differences, particularly the difference in age. In both clouds, a rough estimate of the radial electric field in the rigidly rotating core, calculated in a non-rotating frame, yields values of the order mV m–1.

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