scholarly journals Revisiting the maximum mass of differentially rotating neutron stars in general relativity with realistic equations of state

2019 ◽  
Vol 99 (8) ◽  
Author(s):  
Pedro L. Espino ◽  
Vasileios Paschalidis
Keyword(s):  
General Relativity ◽  
Neutron Stars ◽  
Equations Of State ◽  
Maximum Mass

scholarly journals Neutron Stars in f(R)-Gravity and Its Extension with a Scalar Axion Field

Particles ◽  
2020 ◽  
Vol 3 (3) ◽  
pp. 532-542 ◽  
Author(s):  
Artyom Astashenok ◽  
Sergey Odintsov
Keyword(s):  
General Relativity ◽  
Neutron Stars ◽  
Equations Of State ◽  
Einstein Equations ◽  
Central Density ◽  
Axion Field ◽  
Mass Profile

We present a brief review of general results about non-rotating neutron stars in simple R 2 gravity and its extension with a scalar axion field. Modified Einstein equations are presented for metrics in isotropical coordinates. The mass–radius relation, mass profile and dependence of mass from central density on various equations of state are given in comparison to general relativity.

scholarly journals Neutron stars in Palatini $$R+\alpha R^2$$ and $$R+\alpha R^2+\beta Q$$ theories

2021 ◽  
Vol 81 (10) ◽  
Author(s):  
Georg Herzog ◽  
Hèlios Sanchis-Alepuz
Keyword(s):  
General Relativity ◽  
Equation Of State ◽  
Neutron Stars ◽  
Equations Of State ◽  
Stellar Structure ◽  
Modified Theories Of Gravity ◽  
State Uncertainty ◽  
Structure Equations ◽  
Theories Of Gravity

AbstractWe study solutions of the stellar structure equations for spherically symmetric objects in modified theories of gravity, where the Einstein-Hilbert Lagrangian is replaced by $$f(R)=R+\alpha R^2$$ f ( R ) = R + α R 2 and $$f(R,Q)=R+\alpha R^2+\beta Q$$ f ( R , Q ) = R + α R 2 + β Q , with R being the Ricci scalar curvature, $$Q=R_{\mu \nu }R^{\mu \nu }$$ Q = R μ ν R μ ν and $$R_{\mu \nu }$$ R μ ν the Ricci tensor. We work in the Palatini formalism, where the metric and the connection are assumed to be independent dynamical variables. We focus on stellar solutions in the mass-radius region associated to neutron stars. We illustrate the potential impact of the $$R^2$$ R 2 and Q terms by studying a range of viable values of $$\alpha $$ α and $$\beta $$ β . Similarly, we use different equations of state (SLy, FPS, HS(DD2) and HS(TMA)) as a simple way to account for the equation of state uncertainty. Our results show that for certain combinations of the $$\alpha $$ α and $$\beta $$ β parameters and equation of state, the effect of modifications of general relativity on the properties of stars is sizeable. Therefore, with increasing accuracy in the determination of the equation of state for neutron stars, astrophysical observations may serve as discriminators of modifications of General Relativity.

scholarly journals Neutron stars in frames of R2-gravity and gravitational waves

2019 ◽  
Vol 16 (01) ◽  
pp. 1950004 ◽  
Author(s):  
Artyom V. Astashenok ◽  
Alexey S. Baigashov ◽  
Sergey A. Lapin
Keyword(s):  
General Relativity ◽  
Neutron Stars ◽  
Gravitational Waves ◽  
Simple Formula ◽  
Equations Of State ◽  
Dense Matter ◽  
Dilaton Field ◽  
Spatial Infinity ◽  
Schwarzschild Solution ◽  
Distant Observer

The realistic models of neutron stars are considered for simple [Formula: see text] gravity and equivalent Brance–Dicke theory with dilaton field in Einsein frame. For negative values of [Formula: see text] we have no acceptable results from astrophysical viewpoint: the resulting solution for spherical stars doesn’t coincide with Schwarzschild solution on spatial infinity. The mass of star from viewpoint of distant observer tends to very large values. For [Formula: see text] it is possible to obtain solutions with required asymptotics and well-defined star mass. The mass confined by stellar surface decreases with increasing of [Formula: see text] but we have some contribution to mass from gravitational sphere appearing outside the star. The resulting effect is increasing of gravitational mass from viewpoint of distant observer. But another interpretation take place in a case of equivalent Brance–Dicke theory with massless dilaton field in Einstein frame. The mass of star increases due to contribution of dilaton field inside the star. We also considered the possible constraints on [Formula: see text] gravity from GW 170817 data. According to results of Bauswein et al. the lower limit on threshold mass is [Formula: see text][Formula: see text][Formula: see text]. This allows to exclude some equations of state (EoS) for dense matter. But in [Formula: see text] gravity the threshold mass increases for given EoS with increasing of [Formula: see text]. In principle it can helps in future discriminate between General Relativity and square gravity (of course one need to know EoS with more accuracy rather than now).

EQUATION OF STATE, MASS, RADIUS, MOMENT OF INERTIA, AND SURFACE GRAVITATIONAL REDSHIFT FOR NEUTRON STARS

1994 ◽  
Vol 03 (04) ◽  
pp. 813-838 ◽  
Author(s):  
G. BAO ◽  
E. ØSTGAARD ◽  
B. DYBVIK
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Neutron Stars ◽  
Total Mass ◽  
Equations Of State ◽  
Maximum Mass ◽  
Neutron Star Matter ◽  
Solar Mass ◽  
Moments Of Inertia ◽  
Gravitational Fields

We have calculated total masses and radii of neutron stars from the Tolman-Oppenheimer-Volkoff (TOV) equations (for matter in equilibrium in gravitational fields) and different equations of state for neutron-star matter. The calculations are done for different input central densities. We have also obtained pressure and density as functions of distance from the centre of the star, and moments of inertia and surface gravitational redshifts as functions of the total mass of the star. The maximum mass M max is for all equations of state in our calculations given by 1.65M⊙<M max <2.43M⊙ (where M⊙ is the solar mass), which agrees very well with “experimental” results. Corresponding radii R are given by 8.8 km <R<12.7 km , and a smaller central density will, in general, give a smaller mass and a larger radius.

Rapidly rotating neutron stars in general relativity: Realistic equations of state

1994 ◽  
Vol 424 ◽  
pp. 823 ◽  
Author(s):  
Gregory B. Cook ◽  
Stuart L. Shapiro ◽  
Saul A. Teukolsky
Keyword(s):  
General Relativity ◽  
Neutron Stars ◽  
Equations Of State

Effect of Differential Rotation on the Maximum Mass of Neutron Stars: Realistic Nuclear Equations of State

2004 ◽  
Vol 610 (2) ◽  
pp. 941-947 ◽  
Author(s):  
Ian A. Morrison ◽  
Thomas W. Baumgarte ◽  
Stuart L. Shapiro
Keyword(s):  
Neutron Stars ◽  
Differential Rotation ◽  
Equations Of State ◽  
Maximum Mass

scholarly journals Updated universal relations for tidal deformabilities of neutron stars from phenomenological equations of state

2021 ◽  
Vol 103 (6) ◽  
Author(s):  
Daniel A. Godzieba ◽  
Rossella Gamba ◽  
David Radice ◽  
Sebastiano Bernuzzi
Keyword(s):  
Neutron Stars ◽  
Equations Of State ◽  
Phenomenological Equations
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