Fluid spheres in Einstein–Yukawa theory

1983 ◽  
Vol 61 (2) ◽  
pp. 239-243 ◽  
Author(s):  
K. D. Krori ◽  
R. Bhattacharjee ◽  
Sumita Chaudhury ◽  
Madhumita Barua
Keyword(s):  
Neutron Stars ◽  
Complete Solution ◽  
Positive Pressure ◽  
Order Of Approximation ◽  
Physical Conditions ◽  
Fluid Spheres ◽  
Yukawa Theory

We present here a complete solution (to a certain order of approximation) of fluid spheres in the Einstein–Yukawa theory. It is nonsingular and satisfies physical conditions (positive pressure and density). The solution has some relevance to neutron stars.

Slowly rotating fluid spheres in the Einstein–Yukawa theory

1983 ◽  
Vol 61 (9) ◽  
pp. 1324-1327
Author(s):  
K. D. Krori ◽  
A. R. Sheikh
Keyword(s):  
Analytic Solutions ◽  
The Other ◽  
Slow Rotation ◽  
Rotating Fluid ◽  
Physical Conditions ◽  
Fluid Spheres ◽  
Interior Solutions ◽  
Yukawa Theory

We introduce slow rotation to a solution given by Krori et al. which represents fluid spheres in the Einstein–Yukawa theory, and present two new analytic solutions which are nonsingular and satisfy physical conditions throughout the spheres. One of the interior solutions represents uniformly rotating spheres and the other represents differentially rotating spheres. We also match the interior and exterior solutions on the boundary.

Exact interior solutions in Einstein–Cartan–Yukawa theory

1988 ◽  
Vol 66 (2) ◽  
pp. 126-131
Author(s):  
K. D. Krori ◽  
P. Borgohain ◽  
Kanika Das ◽  
Arunima Sarma
Keyword(s):  
Massive Star ◽  
The Other ◽  
Simple Method ◽  
Physical Conditions ◽  
Interior Solutions ◽  
Yukawa Theory

A simple method of obtaining singularity-free interior solutions in Einstein–Cartan–Yukawa theory is presented here. The validity of the solution is shown by considering two types of configurations, one Schwarzschild-like and the other Tolman-IV-like. We recover the Schwarzschild and Tolman-IV solutions as soon as the Cartan and Yukawa effects are switched off. In both cases the necessary physical conditions are satisfied. The possible role of torsion in halting the collapse of a massive star is also studied.

scholarly journals Equatorial Geodesics Around the Magnetars

2017 ◽  
Vol 45 ◽  
pp. 1760050
Author(s):  
Viviane A. P. Alfradique ◽  
Orlenys N. Troconis ◽  
Rodrigo P. Negreiros
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Neutron Stars ◽  
Complete Solution ◽  
Compact Object ◽  
Relativistic Effects ◽  
Schwarzschild Solution ◽  
Soft Gamma Repeaters ◽  
Definition Of ◽  
The Magnetic Field

Neutron stars manifest themselves as different classes of astrophysical sources that are associated to distinct phenomenology. Here we focus our attention on magnetars (or strongly magnetized neutron stars) that are associated to Soft Gamma Repeaters and Anomalous X-ray Pulsars. The magnetic field on surface of these objects, reaches values greater than [Formula: see text] G. Under intense magnetic fields, relativistic effects begin to be decisive for the definition of the structure and evolution of these objects. We are tempted to question ourselves to how strengths fields affect the structure of neutron star. In this work, our objective is study and compare two solutions of Einstein-Maxwell equations: the Bonnor solution, which is an analytical solution that describe the exterior spacetime for a massive compact object which has a magnetic field that is characterize as a dipole field and a complete solution that describe the interior and exterior spacetime for the same source found by numerical methods). For this, we describe the geodesic equations generated by such solutions. Our results show that the orbits generated by the Bonnor solution are the same as described by numerical solution. Also, show that the inclusion of magnetic fields with values up to [Formula: see text]G in the center of the star does not modify sharply the particle orbits described around this star, so the use of Schwarzschild solution for the description of these orbits is a reasonable approximation.

The XMM-NEWTON VIEW ON NEUTRON STARS AND BLACK HOLES

2004 ◽  
Vol 13 (07) ◽  
pp. 1229-1237
Author(s):  
CHRISTIAN MOTCH
Keyword(s):  
Black Holes ◽  
Spectral Analysis ◽  
Neutron Stars ◽  
Binary Systems ◽  
Short Review ◽  
High Energy ◽  
Compact Objects ◽  
High Energy Resolution ◽  
X Ray ◽  
Physical Conditions

The improved sensitivity of the XMM-Newton satellite is quickly expanding our knowledge of X-ray emission mechanisms and physical conditions in and around compact objects. Thanks to the large collecting power and high energy resolution of the EPIC and RGS instruments, detailed X-ray spectral analysis can be performed in the 0.2 to 12 keV energy range. In this short review, I highlight the most significant results obtained by XMM-Newton on neutron stars both isolated and in binary systems and on accreting stellar mass black holes.

scholarly journals Nonlocal equation of state in anisotropic static fluid spheres in general relativity

2004 ◽  
Vol 82 (1) ◽  
pp. 29-51 ◽  
Author(s):  
H Hernández ◽  
L A Núñez
Keyword(s):  
Equation Of State ◽  
Radial Pressure ◽  
Spherically Symmetric ◽  
Density Profiles ◽  
Physical Conditions ◽  
Tangential Stresses ◽  
Nonlocal Equation ◽  
Static Fluid ◽  
Anisotropic Fluids ◽  
Fluid Spheres

We show that it is possible to obtain, at least certain regions within spherically symmetric static matter configurations, credible anisotropic fluids satisfying a nonlocal equation of state. This particular type of equation of state provides, at a given point, the radial pressure not only as a function of the density at that point, but its functional throughout the enclosed distribution. To establish the physical plausibility of the proposed family of solutions satisfying a nonlocal equation of state, we study the constraints imposed by the junction, energy, and some intuitive physical conditions. We show that these static fluids having this particular equation of state are "naturally" anisotropic in the sense that they satisfy, identically, the anisotropic Tolman–Oppenheimer–Volkov equation. We also show that it is possible to obtain physically plausible static anisotropic spherically symmetric matter configurations starting from known density profiles, and also for configurations where tangential pressures vanish. This very particular type of relativistic sphere with vanishing tangential stresses is inspired by some of the models proposed to describe extremely magnetized neutron stars (magnetars) during the transverse quantum collapse.

The propagation of steady disturbances in a supersonic stream bounded on one side by a parallel subsonic stream

1948 ◽  
Vol 44 (3) ◽  
pp. 380-390 ◽  
Author(s):  
L. Howarth
Keyword(s):  
Incident Wave ◽  
Pressure Pulse ◽  
Complete Solution ◽  
Initial Disturbance ◽  
Positive Pressure ◽  
Supersonic Stream ◽  
Reflected Wave ◽  
Axis Of Symmetry ◽  
Subsonic Region

The problem of the propagation of steady disturbance in a semi-infinite supersonic stream moving parallel to and bounded on one side by a subsonic stream is discussed and the complete solution obtained for any assumed form of incident disturbance. It is shown that a local initial disturbance generally produces a reflected wave extending to infinity both upstream and downstream of the initial disturbance. A (positive) pressure pulse as an incident wave produces pressure upstream and rarefaction downstream and the magnitude of the effects is calculated in a particular case. Conditions along the axis of symmetry are calculated for the subsonic region in this case.

scholarly journals Neutron star structure in the presence of conformally coupled scalar fields

2014 ◽  
Vol 23 (11) ◽  
pp. 1450090 ◽  
Author(s):  
Joseph Sultana ◽  
Benjamin Bose ◽  
Demosthenes Kazanas
Keyword(s):  
Neutron Star ◽  
Scalar Field ◽  
Neutron Stars ◽  
Equations Of State ◽  
Complete Solution ◽  
Scalar Fields ◽  
Star Models ◽  
Neutron Star Mass ◽  
Theories Of Gravity ◽  
Star Structure

Neutron star models are studied in the context of scalar–tensor theories of gravity in the presence of a conformally coupled scalar field, using two different numerical equations of state (EoS) representing different degrees of stiffness. In both cases we obtain a complete solution by matching the interior numerical solution of the coupled Einstein-scalar field hydrostatic equations, with an exact metric on the surface of the star. These are then used to find the effect of the scalar field and its coupling to geometry, on the neutron star structure, particularly the maximum neutron star mass and radius. We show that in the presence of a conformally coupled scalar field, neutron stars are less dense and have smaller masses and radii than their counterparts in the minimally coupled case, and the effect increases with the magnitude of the scalar field at the center of the star.

Influence of Magnetic Fields on Solar Hydrodynamics: Experimental Results

1977 ◽  
Vol 36 ◽  
pp. 143-180 ◽  
Author(s):  
J.O. Stenflo
Keyword(s):  
Solar Activity ◽  
Energy Balance ◽  
Magnetic Fields ◽  
Solar Atmosphere ◽  
General Problem ◽  
Solar Rotation ◽  
Active Regions ◽  
Physical Conditions ◽  
Dynamic Phenomena

It is well-known that solar activity is basically caused by the Interaction of magnetic fields with convection and solar rotation, resulting in a great variety of dynamic phenomena, like flares, surges, sunspots, prominences, etc. Many conferences have been devoted to solar activity, including the role of magnetic fields. Similar attention has not been paid to the role of magnetic fields for the overall dynamics and energy balance of the solar atmosphere, related to the general problem of chromospheric and coronal heating. To penetrate this problem we have to focus our attention more on the physical conditions in the ‘quiet’ regions than on the conspicuous phenomena in active regions.

Positive Pressure

2006 ◽  
Vol 31 (11) ◽  
pp. 48-62 ◽  
Author(s):  
James F. Goss ◽  
Jonathan Zygowiec
Keyword(s):  
Positive Pressure
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