scholarly journals Plausible families of compact objects with a nonlocal equation of state

2013 ◽  
Vol 91 (4) ◽  
pp. 328-336 ◽  
Author(s):  
H. Hernández ◽  
L.A. Núñez
Keyword(s):  
Equation Of State ◽  
Total Mass ◽  
Radial Pressure ◽  
Compact Objects ◽  
Einstein Equations ◽  
Matter Distribution ◽  
Nonlocal Equation ◽  
The Family ◽  
Model Independent ◽  
Physical Variables

We present the plausibility of some models emerging from an algorithm devised to generate a one-parameter family of interior solutions for the Einstein equations. We explore how their physical variables change as the family parameter varies. The models studied correspond to anisotropic spherical matter configurations having a nonlocal equation of state. This particular type of equation of state, with no causality problems, provides at a given point the radial pressure not only as a function of the density but as a functional of the enclosed matter distribution. We have found that there are several model-independent tendencies as the parameter increases: the equation of state tends to be stiffer and the total mass becomes half of its external radius. Profiting from the concept of cracking of materials in general relativity, we obtain that these models become more potentially stable as the family parameter increases.

Charged anisotropic static cylindrically symmetric models

2013 ◽  
Vol 91 (2) ◽  
pp. 113-119 ◽  
Author(s):  
M. Sharif ◽  
H. Ismat Fatima
Keyword(s):  
Electromagnetic Field ◽  
Equation Of State ◽  
Energy Density ◽  
Symmetric Space ◽  
Radial Pressure ◽  
Matter Distribution ◽  
Field Equations ◽  
Stellar Objects ◽  
Cylindrically Symmetric ◽  
Barotropic Equation

In this paper, we investigate exact solutions of the field equations for charged, anisotropic, static, cylindrically symmetric space–time. We use a barotropic equation of state linearly relating the radial pressure and energy density. The analysis of the matter variables indicates a physically reasonable matter distribution. In the most general case, the central densities correspond to realistic stellar objects in the presence of anisotropy and charge. Finally, we conclude that matter sources are less affected by the electromagnetic field.

A New Model for Charged Anisotropic Matter with Modified Chaplygin Equation of State

2020 ◽  
Author(s):  
Manuel Malaver ◽  
Hamed Daei Kasmaei
Keyword(s):  
Equation Of State ◽  
Energy Density ◽  
Compact Star ◽  
Radial Pressure ◽  
Extended Version ◽  
Matter Distribution ◽  
Field Equations ◽  
New Model ◽  
Anisotropic Matter ◽  
Chaplygin Equation

In this paper, we found a new model for compact star with charged anisotropic matter distribution considering an extended version of the Chaplygin equation of state. We specify a particular form of the metric potential Z(x) that allows us to solve the Einstein-Maxwell field equations. The obtained model satisfies all physical properties expected in a realistic star such that the expressions for the radial pressure, energy density, metric coefficients, measure of anisotropy and the mass are fully well defined and are regular in the interior of star. The solution obtained in this work can have multiple applications in astrophysics and cosmology.

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.

scholarly journals ELECTROMAGNETIC FIELD IN SOME ANISOTROPIC STIFF FLUID UNIVERSES

1995 ◽  
Vol 10 (28) ◽  
pp. 2095-2101 ◽  
Author(s):  
LUIS O. PIMENTEL
Keyword(s):  
Electromagnetic Field ◽  
Equation Of State ◽  
Exact Solutions ◽  
Perfect Fluid ◽  
Einstein Equations ◽  
Stiff Fluid ◽  
Field Equations ◽  
Material Content ◽  
Stiff Equation ◽  
The Family

The electromagnetic field is studied in a family of exact solutions of the Einstein equations whose material content is a perfect fluid with stiff equation of state (p=ε). The field equations are solved exactly for several members of the family.

scholarly journals Mass-radius relation of compact objects

2019 ◽  
Vol 15 (S356) ◽  
pp. 383-384
Author(s):  
Seman Abaraya ◽  
Tolu Biressa
Keyword(s):  
Numerical Analysis ◽  
Equation Of State ◽  
Compact Objects ◽  
Mass Limit ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Formation And Evolution ◽  
Active Research ◽  
Compact Sources ◽  
Astrophysical Research

AbstractCompact objects are of great interest in astrophysical research. There are active research interests in understanding better various aspects of formation and evolution of these objects. In this paper we addressed some problems related to the compact objects mass limit. We employed Einstein field equations (EFEs) to derive the equation of state (EoS). With the assumption of high densities and low temperature of compact sources, the derived equation of state is reduced to polytropic kind. Studying the polytropic equations we obtained similar physical implications, in agreement to previous works. Using the latest version of Mathematica-11 in our numerical analysis, we also obtained similar results except slight differences in accuracy.

scholarly journals DARK MATTER DYNAMICS AND INDIRECT DETECTION

2005 ◽  
Vol 20 (14) ◽  
pp. 1021-1036 ◽  
Author(s):  
GIANFRANCO BERTONE ◽  
DAVID MERRITT
Keyword(s):  
Dark Matter ◽  
Total Mass ◽  
Galactic Center ◽  
Direct Detection ◽  
Indirect Detection ◽  
Matter Distribution ◽  
Dark Matter Distribution ◽  
Particle Dark Matter ◽  
The Universe ◽  
Rule Out

Non-baryonic, or "dark", matter is believed to be a major component of the total mass budget of the Universe. We review the candidates for particle dark matter and discuss the prospects for direct detection (via interaction of dark matter particles with laboratory detectors) and indirect detection (via observations of the products of dark matter self-annihilations), focusing in particular on the Galactic center, which is among the most promising targets for indirect detection studies. The gravitational potential at the Galactic center is dominated by stars and by the supermassive black hole, and the dark matter distribution is expected to evolve on sub-parsec scales due to interaction with these components. We discuss the dominant interaction mechanisms and show how they can be used to rule out certain extreme models for the dark matter distribution, thus increasing the information that can be gleaned from indirect detection searches.

An anisotropic charged fluids with Chaplygin equation of state

2021 ◽  
Vol 36 (21) ◽  
pp. 2150153
Author(s):  
Joaquin Estevez-Delgado ◽  
Noel Enrique Rodríguez Maya ◽  
José Martínez Peña ◽  
Arthur Cleary-Balderas ◽  
Jorge Mauricio Paulin-Fuentes
Keyword(s):  
Speed Of Sound ◽  
Radial Pressure ◽  
State Equation ◽  
Stellar Model ◽  
Compact Objects ◽  
Anisotropic Fluid ◽  
The Stability ◽  
Electrically Charged ◽  
Chaplygin Equation ◽  
Graphic Description

A stellar model with an electrically charged anisotropic fluid as a source of matter is presented. The radial pressure is described by a Chaplygin state equation, [Formula: see text], while the anisotropy [Formula: see text] is annulled in the center of the star [Formula: see text] is regular and [Formula: see text], the electric field, is also annulled in the center. The density pressures and the tangential speed of sound are regular, while the radial speed of sound is monotonically increasing. The model is physically acceptable and meets the stability criteria of Harrison–Zeldovich–Novikov and in respect of the cracking concept the solution is unstable in the region of the center and potentially stable near the surface. A graphic description is presented for the case of an object with a compactness rate [Formula: see text], mass [Formula: see text] and radius [Formula: see text] km that matches the star Vela X-1. Also, the interval of the central density [Formula: see text], which is consistent with the expected magnitudes for this type of stars, which shows that the behavior is accurate for describing compact objects.

scholarly journals “TNOs are Cool”: A survey of the trans-Neptunian region

2018 ◽  
Vol 618 ◽  
pp. A136 ◽  
Author(s):  
E. Vilenius ◽  
J. Stansberry ◽  
T. Müller ◽  
M. Mueller ◽  
C. Kiss ◽  
...  
Keyword(s):  
Power Law ◽  
Total Mass ◽  
Size Range ◽  
Family Members ◽  
Far Infrared ◽  
Effective Diameter ◽  
Water Ice ◽  
The Family ◽  
The Individual ◽  
Geometric Albedo

Context. A group of trans-Neptunian objects (TNOs) are dynamically related to the dwarf planet 136108 Haumea. Ten of them show strong indications of water ice on their surfaces, are assumed to have resulted from a collision, and are accepted as the only known TNO collisional family. Nineteen other dynamically similar objects lack water ice absorptions and are hypothesized to be dynamical interlopers. Aims. We have made observations to determine sizes and geometric albedos of six of the accepted Haumea family members and one dynamical interloper. Ten other dynamical interlopers have been measured by previous works. We compare the individual and statistical properties of the family members and interlopers, examining the size and albedo distributions of both groups. We also examine implications for the total mass of the family and their ejection velocities. Methods. We use far-infrared space-based telescopes to observe the target TNOs near their thermal peak and combine these data with optical magnitudes to derive sizes and albedos using radiometric techniques. Using measured and inferred sizes together with ejection velocities, we determine the power-law slope of ejection velocity as a function of effective diameter. Results. The detected Haumea family members have a diversity of geometric albedos ~0.3–0.8, which are higher than geometric albedos of dynamically similar objects without water ice. The median geometric albedo for accepted family members is pV = 0.48−0.18+0.28, compared to 0.08−0.05+0.07 for the dynamical interlopers. In the size range D = 175−300 km, the slope of the cumulative size distribution is q = 3.2−0.4+0.7 for accepted family members, steeper than the q = 2.0 ± 0.6 slope for the dynamical interlopers with D < 500 km. The total mass of Haumea’s moons and family members is 2.4% of Haumea’s mass. The ejection velocities required to emplace them on their current orbits show a dependence on diameter, with a power-law slope of 0.21–0.50.

scholarly journals A Sterile Neutrino Scenario Constrained By Experiments and Cosmology

1997 ◽  
Vol 12 (21) ◽  
pp. 3669-3694 ◽  
Author(s):  
Nobuchika Okada ◽  
Osamu Yasuda
Keyword(s):  
Total Mass ◽  
Sterile Neutrino ◽  
Neutrinoless Double Beta Decay ◽  
Big Bang ◽  
Double Beta Decay ◽  
Big Bang Nucleosynthesis ◽  
Negative Results ◽  
Equivalent Number ◽  
Mixing Matrix ◽  
Model Independent

We analyze a scheme in which three active neutrinos and one sterile neutrino account for the solar, the atmospheric and the LSND neutrino anomalies in a model-independent way. It is shown that if the equivalent number, Nν, of the light neutrino species is less than 4, then the constraints from these anomalies, accelerator and reactor experiments and big bang nucleosynthesis force a general 4 × 4 mixing matrix to be effectively split into two 2 × 2 matrices. If these neutrinos are of the Majorana type, then negative results of neutrinoless double beta decay experiments imply that the total mass of neutrinos is not sufficient to account for all the hot dark matter components.

A generalized anisotropic model for super dense stars

2021 ◽  
pp. 2150070
Author(s):  
Joaquin Estevez-Delgado ◽  
Gabino Estevez-Delgado ◽  
Noel Enrique Rodríguez Maya ◽  
José Martínez Peña ◽  
Aurelio Tamez Murguía
Keyword(s):  
Radial Pressure ◽  
Compact Stars ◽  
Anisotropic Model ◽  
Speed Of Light ◽  
Matter Distribution ◽  
Sphere Model ◽  
Tangential Pressure ◽  
Relativistic Fluid ◽  
Causal Condition ◽  
Dense Stars

A static anisotropic relativistic fluid sphere model with regular geometry and finite hydrostatic functions is presented. In the interior of the sphere, the density, radial pressure and tangential pressure are positives, monotonically decreasing with increasing radius and the radial pressure vanishes at the surface of the matter distribution and is joined continuously to the exterior Schwarzschild’s solution at this surface. The speeds of the radial and tangential sound are positive and lower than the speed of light, that is, the causal condition is not violated, and also the behavior of these guarantees that the model is potentially stable. Furthermore, the range of the compactness ratio is characteristic of compact stars and it is shown that the effect of the anisotropy generates that the speed of the radial sound can behave as a function monotonically increasing or monotonically decreasing.

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