A perfect fluid model for neutron stars

2018 ◽  
Vol 33 (40) ◽  
pp. 1850237 ◽  
Author(s):  
Gabino Estevez-Delgado ◽  
Joaquin Estevez-Delgado ◽  
Nadiezhda Montelongo Garcia ◽  
Modesto Pineda Duran
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Perfect Fluid ◽  
Fluid Model ◽  
Compact Stars ◽  
The Sun ◽  
Speed Of Light ◽  
Internal Solution ◽  
Maximum Value ◽  
Decreasing Functions

In this paper, we present a physically acceptable internal solution with a perfect fluid, which needs the pressure and density as regular, positive and monotonic decreasing functions and with a speed of sound positive and lower than the speed of light. This solution depends on a parameter [Formula: see text], and it is physically acceptable if [Formula: see text], the compactness has a maximum value for the maximum value of [Formula: see text] and it corresponds to [Formula: see text], thus the model can be applicable to the description of compact stars. In a complementary way, we present the description of a star with mass equal to the sun mass and radius of [Formula: see text] Km associated to the neutron star Her X-1, obtaining a central density [Formula: see text] which is characteristic of the neutron stars.

Black Hole, Neutron Star and Numerical Relativity

2021 ◽  
Vol 30 (6) ◽  
pp. 7-13
Author(s):  
Jinho KIM
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Black Hole ◽  
Neutron Star ◽  
Neutron Stars ◽  
Numerical Method ◽  
High Velocity ◽  
Compact Objects ◽  
Compact Stars ◽  
Speed Of Light

Compact stars, e.g., black holes and neutron stars, are the most energetic objects in astrophysics. These objects are accompanied by extremely strong gravity and a high velocity, which approaches the speed of light. Therefore, compact objects should be dealt with in Einstein’s relativity. This article will briefly introduce a numerical method that will allow us to obtain general solutions in general relativity. Several applications using numerical relativistic simulations will also be presented.

A regular perfect fluid model for dense stars

2019 ◽  
Vol 34 (15) ◽  
pp. 1950115 ◽  
Author(s):  
Gabino Estevez-Delgado ◽  
Joaquin Estevez-Delgado ◽  
Jorge Mauricio Paulin-Fuentes ◽  
Nadiezhda Montelongo Garcia ◽  
Modesto Pineda Duran
Keyword(s):  
Perfect Fluid ◽  
Fluid Model ◽  
Einstein Equations ◽  
Compact Stars ◽  
Variable Pressure ◽  
Spherically Symmetric ◽  
Matter Distribution ◽  
Stellar Objects ◽  
Dense Stars ◽  
Decreasing Functions

We present an exact regular solution of Einstein equations for a static and spherically symmetric spacetime with a matter distribution of isotropic perfect fluid. The construction of the solution is realized assigning a regular potential [Formula: see text] and integrating the isotropic perfect fluid condition for the pressure. The resulting solution is physically acceptable, i.e. the geometry is regular and the hydrostatic variable pressure and density are positive regular monotonic decreasing functions, the speed of the sound is positive and smaller than the speed of the light. An important element of this solution is that its compactness value [Formula: see text] is in the characteristic range of compact stars, which makes a remarkable difference with other models with isotropic perfect fluid, this is [Formula: see text] so that we could represent compact stellar objects as neutron stars. In particular, for the maximum compactness of a star with a mass of [Formula: see text] the radius is [Formula: see text] and their central density [Formula: see text] is characteristic of compact stars.

scholarly journals Quadrupole moments of rotating compact stars

2012 ◽  
Vol 8 (S291) ◽  
pp. 536-536
Author(s):  
Martin Urbanec ◽  
John Miller ◽  
Zdenek Stuchlik
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Neutron Stars ◽  
Strange Star ◽  
Compact Stars ◽  
Quadrupole Moments ◽  
Strange Stars

AbstractWe present quadrupole moments of rotating neutron and strange stars calculated using standard Hartle Thorne approach. We demonstrate differences between neutron and strange star parameters connected with quadrupole moments and how this parameters could be, in the case of neutron stars, approximated almost independently on neutron star equation of state.

scholarly journals Detecting UV Radiation from Nearby Pulsars with the Hubble Space Telescope

1992 ◽  
Vol 128 ◽  
pp. 220-221
Author(s):  
George G. Pavlov
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Thermal Radiation ◽  
Neutron Stars ◽  
Hubble Space Telescope ◽  
Thermal Evolution ◽  
The Sun ◽  
Space Telescope ◽  
Additional Constraints ◽  
Relativistic Particles

AbstractEven old (106 to 107 yr) pulsars within a few hundred parsecs of the Sun should give UV and optical fluxes via thermal radiation or radiation from relativistic particles. The surface temperature of a neutron star depends on its mass, radius, magnetic field, and internal composition (existence of pion condensate, superfluidity of nucléons, etc.). If the temperature exceeds ~2x104 K, the thermal radiation can be detected by the Hubble Space Telescope. An analysis of the results will allow one to study the thermal evolution and inner structure of neutron stars in order to obtain additional constraints on pulsar models.

scholarly journals A perfect fluid model for compact stars

2019 ◽  
Vol 97 (9) ◽  
pp. 988-993 ◽  
Author(s):  
Gabino Estevez-Delgado ◽  
Joaquin Estevez-Delgado ◽  
Nadiezhda Montelongo García ◽  
Modesto Pineda Duran
Keyword(s):  
Perfect Fluid ◽  
Fluid Model ◽  
Compact Stars

scholarly journals Anisotropic neutron stars by gravitational decoupling

2019 ◽  
Vol 79 (10) ◽  
Author(s):  
V. A. Torres-Sánchez ◽  
E. Contreras
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Perfect Fluid ◽  
Compact Object ◽  
Adiabatic Index ◽  
X Ray ◽  
Binary Pulsar ◽  
Stable Solutions ◽  
X Ray Binaries ◽  
Fluid Configuration

Abstract In this work we obtain an anisotropic neutron star solution by gravitational decoupling starting from a perfect fluid configuration which has been used to model the compact object PSR J0348+0432. Additionally, we consider the same solution to model the Binary Pulsar SAX J1808.4-3658 and X-ray Binaries Her X-1 and Cen X-3 ones. We study the acceptability conditions and obtain that the MGD-deformed solution obey the same physical requirements as its isotropic counterpart. Finally, we conclude that the most stable solutions, according to the adiabatic index and gravitational cracking criterion, are those with the smallest compactness parameters, namely SAX J1808.4-3658 and Her X-1.

scholarly journals Neutron Stars, Strange Pulsars and Strange Dwarfs

1996 ◽  
Vol 160 ◽  
pp. 135-136
Author(s):  
Fridolin Weber ◽  
Norman K. Glendenning
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Strong Interaction ◽  
Ground State ◽  
Strange Quark ◽  
Complete Sequence ◽  
Strange Quark Matter ◽  
Compact Stars ◽  
Strange Dwarfs ◽  
Separate Class

The hypothesis that strange quark matter may be the absolute ground state of the strong interaction (not56Fe) has been raised independently by Boder and Witten. If the hypothesis is true, then a separate class of compact stars could exist, which are calledstrange matter stars. The properties of the complete sequence of such stars, which range from compact neutron-star-like strange stars to strange dwarfs to strange planets. The latter two constitute the strange counterparts of ordinary white dwarfs and planets, respectively. The properties of these objects are discussed in this paper.

scholarly journals A charged perfect fluid model with high compactness

2019 ◽  
Vol 65 (4 Jul-Aug) ◽  
pp. 382 ◽  
Author(s):  
G. Estevez-Delgado ◽  
J. Estevez-Delgado ◽  
M. Pineda Duran ◽  
N. Montelongo García ◽  
J.M. Paulin-Fuentes
Keyword(s):  
Electric Field ◽  
Perfect Fluid ◽  
Maxwell Equations ◽  
Fluid Model ◽  
Stellar Model ◽  
Compact Stars ◽  
Charged Fluid ◽  
Charge Parameter ◽  
Positive Functions ◽  
Increasing Function

A relativistic, static and spherically symmetrical stellar model is presented, constituted by a perfect charged fluid. This represents a generalization to the case of a perfect neutral fluid, whose construction is made through the solution to the Einstein-Maxwell equations proposing a form of gravitational potential  $g_{tt}$ and the electric field. The choice of electric field implies that this model supports values of compactness$u=GM/c^2R\leq 0.5337972212$, values higher than the case without electric charge ($u\leq 0.3581350065$), being this feature of relevance to get to represent compact stars. In addition, density and pressure are positive functions, bounded and decreasing monotones, the electric field is a monotonously increasing function as well as satisfying the condition of causality so the model is physically acceptable. In a complementary way, the internal behavior of the hydrostatic functions and their values are obtained taking as a data the corresponding to a star of $1 M_\odot$,for different values of the charge parameter, obtaining an interval for the central density $\rho_c\approx (7.9545,2.7279) 10^{19}$ $ Kg/m^3$ characteristic of compact stars.

A uniparametric perfect fluid solution to represent compact stars

2021 ◽  
Vol 36 (10) ◽  
pp. 2150068
Author(s):  
Joaquin Estevez-Delgado ◽  
Noel Enrique Rodríguez Maya ◽  
José Martínez Peña ◽  
David Rivera Rangel ◽  
Nancy Cambron Muñoz
Keyword(s):  
Neutron Stars ◽  
Perfect Fluid ◽  
Stellar Model ◽  
Compact Objects ◽  
Compact Stars ◽  
Index Formula ◽  
Perfect Fluid Solution ◽  
Gravitational Theories ◽  
State Formula ◽  
The Stability

In the description of neutron stars, it is very important to consider gravitational theories as general relativity, due to the determining influence on the behavior of the different types of stars, since some objects show densities even bigger than nuclear density. This paper starts with Einstein’s equations for a perfect fluid and then we present a uniparametric stellar model which allows to describe compact objects like neutron stars with compactness ratio [Formula: see text]. The pressure and density are monotone decreasing regular functions, the speed of sound satisfies the causality condition, while the value for its adiabatic index [Formula: see text] guarantees the stability. In addition, the graph of [Formula: see text] versus [Formula: see text] shows a quasi-linear relationship for the equation of state [Formula: see text], which is similar to the so-called MIT Bag equation when we have the interaction between quarks. In our case it is due to the interaction of the different components found inside the star, such as electrons and neutrons. As an application of the model, we describe the star PSR J1614-2230 with a observed mass of [Formula: see text] and a radius [Formula: see text], the model shows that the maximum central density occurs for a maximal compactness value [Formula: see text].

IMPULSIVE LIGHT-LIKE SIGNALS

2002 ◽  
Vol 17 (20) ◽  
pp. 2746-2746
Author(s):  
C. BARRABÈS ◽  
P. A. HOGAN
Keyword(s):  
Black Holes ◽  
Neutron Star ◽  
Neutron Stars ◽  
Gravitational Wave ◽  
Gravitational Radiation ◽  
High Speed ◽  
Compact Objects ◽  
Speed Of Light ◽  
Gravitational Fields ◽  
Multipole Source

A general characterisation of an impulsive light–like signal was given1,2. The signal may consist of a shell of null matter and/or an impulsive gravitational wave. Both parts of the signal can be unambiguously identified3,4. The signals can be used to model bursts of gravitational radiation and light– like matter accompanying cataclysmic events such as supernovae and neutron star collisions. Also in high speed collisions of compact objects such as black–holes or neutron stars the gravitational fields of these objects resemble those of impulsive light–like signals when the objects are boosted to the speed of light. Several examples of impulsive light–like signals were presented, in particular those produced by recoil effects5 and by the Aichelburg–Sexl boost of an isolated gravitating multipole source6. The detection of these signals was also discussed7.

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