scholarly journals Rotating neutron stars in F(R) gravity with axions

2020 ◽  
Vol 498 (3) ◽  
pp. 3616-3623
Author(s):  
Artyom V Astashenok ◽  
Sergey D Odintsov
Keyword(s):  
General Relativity ◽  
Neutron Stars ◽  
Compact Stars ◽  
Static Case ◽  
Rotating Stars ◽  
New Class ◽  
Equilibrium Configurations ◽  
Axion Field ◽  
Central Energy ◽  
Fast Rotating

ABSTRACT We investigate equilibrium configurations of uniformly rotating neutron stars in R2 gravity with axion scalar field for GM1 equation of state (EoS) for nuclear matter. The mass–radius diagram, mass–central energy density are presented for some frequencies in comparison with static stars. We also compute equatorial and polar radii and moment of inertia for stars. For axion field ϕ, the coupling in the form ∼R2ϕ is assumed. Several interesting results follow from our consideration. Maximal possible star mass with given EoS increases due to the contribution of coupling term. We discovered the possibility to increase maximal frequency of the rotation in comparison with General Relativity. As a consequence, the lower bound on mass of the fast rotating stars decreases. For frequency f = 700 Hz, neutron stars with masses ∼M⊙ can exist for some choice of parameters (in General Relativity for same EoS, this limit is around 1.2 M⊙). Another feature of our solutions is relatively small increase of stars' radii for high frequencies in comparison with static case. Thus, eventually, the new class of neutron stars in R2 gravity with axions is discovered namely fast rotating compact stars with intermediate masses.

scholarly journals A new class of analytical solutions describing anisotropic neutron stars in general relativity

2021 ◽  
pp. 2150091
Author(s):  
Jay Solanki ◽  
Bhashin Thakore
Keyword(s):  
General Relativity ◽  
Neutron Stars ◽  
Analytical Solutions ◽  
Radial Pressure ◽  
Compact Stars ◽  
Theory Of Relativity ◽  
Field Equations ◽  
Inherent Anisotropy ◽  
Anisotropic Matter ◽  
New Class

A new class of solutions describing analytical solutions for compact stellar structures has been developed within the tenets of General Relativity. Considering the inherent anisotropy in compact stars, a stable and causal model for realistic anisotropic neutron stars was obtained using the general theory of relativity. Assuming a physically acceptable nonsingular form of one metric potential and radial pressure containing the curvature parameter [Formula: see text], the constant [Formula: see text] and the radius [Formula: see text], analytical solutions to Einstein’s field equations for anisotropic matter distribution were obtained. Taking the value of [Formula: see text] as −0.44, it was found that the proposed model obeys all necessary physical conditions, and it is potentially stable and realistic. The model also exhibits a linear equation of state, which can be applied to describe compact stars.

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.

P-STARS

2004 ◽  
Vol 13 (09) ◽  
pp. 1917-1926 ◽  
Author(s):  
PAOLO CEA
Keyword(s):  
Dark Matter ◽  
Neutron Stars ◽  
Observational Data ◽  
Gravitational Collapse ◽  
Cold Dark Matter ◽  
Compact Stars ◽  
Cooling Curves ◽  
New Class

P-Stars are a new class of compact stars made of up and down quarks in β-equilibrium with electrons in an Abelian chromomagnetic condensate. We show that P-Stars are able to account for compact stars with R≲6 Km , as well as stars with radius comparable with canonical Neutron Stars. We find that cooling curves of P-Stars compare rather well with observational data. We suggest that P-Matter produced at the primordial deconfinement transition is a viable candidate for baryonic Cold Dark Matter. Finally, we show that P-Stars are able to overcome the gravitational collapse even for masses much greater than 106 M⊙.

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.

scholarly journals Are the stars of a new class of variability detected in NGC 3766 fast rotating SPB stars?

2014 ◽  
Vol 9 (S307) ◽  
pp. 188-193
Author(s):  
S. J. A. J. Salmon ◽  
J. Montalbán ◽  
D. R. Reese ◽  
M.-A. Dupret ◽  
P. Eggenberger
Keyword(s):  
Variable Stars ◽  
Coriolis Effect ◽  
Rotating Stars ◽  
Instability Strip ◽  
Visibility Analysis ◽  
New Class ◽  
Low Mass ◽  
Fast Rotating ◽  
Hr Diagram ◽  
As If

AbstractA recent photometric survey in the NGC 3766 cluster led to the detection of stars presenting an unexpected variability. They lie in a region of the Hertzsprung-Russell (HR) diagram where no pulsation are theoretically expected, in between the δ Scuti and slowly pulsating B (SPB) star instability domains. Their variability periods, between ~0.1–0.7 d, are outside the expected domains of these well-known pulsators. The NCG 3766 cluster is known to host fast rotating stars. Rotation can significantly affect the pulsation properties of stars and alter their apparent luminosity through gravity darkening. Therefore we inspect if the new variable stars could correspond to fast rotating SPB stars. We carry out instability and visibility analysis of SPB pulsation modes within the frame of the traditional approximation. The effects of gravity darkening on typical SPB models are next studied. We find that at the red border of the SPB instability strip, prograde sectoral (PS) modes are preferentially excited, with periods shifted in the 0.2–0.5 d range due to the Coriolis effect. These modes are best seen when the star is seen equator-on. For such inclinations, low-mass SPB models can appear fainter due to gravity darkening and as if they were located between the δ Scuti and SPB instability strips.

scholarly journals Supermassive neutron stars in axion F(R) gravity

2020 ◽  
Vol 493 (1) ◽  
pp. 78-86 ◽  
Author(s):  
Artyom V Astashenok ◽  
Sergey D Odintsov
Keyword(s):  
Equation Of State ◽  
Neutron Stars ◽  
Scalar Curvature ◽  
Equations Of State ◽  
Compact Stars ◽  
Axion Mass ◽  
Axion Field ◽  
Wide Range ◽  
Star Surface ◽  
Effective Contribution

ABSTRACT We investigated realistic neutron stars in axion R2 gravity. The coupling between curvature and axion field ϕ is assumed in the simple form ∼R2ϕ. For the axion mass in the range ma ∼ 10−11–10−10 eV the solitonic core within neutron star and corresponding halo with size ∼100 km can exist. Therefore the effective contribution of R2 term grows inside the star and it leads to change of star parameters (namely, mass, and radius). We obtained the increase of star mass independent from central density for wide range of masses. Therefore, maximal possible mass for given equation of state grows. At the same time, the star radius increases not so considerably in comparison with GR. Hence, our model may predict possible existence of supermassive compact stars with masses $M\sim 2.2\!-\!2.3\, \mathrm{M}_\odot$ and radii Rs ∼ 11 km for realistic equation of state (we considered APR equation of state). In general relativity one can obtain neutron stars with such characteristics only for unrealistic, extremely stiff equations of state. Note that this increase of mass occurs due to change of solution for scalar curvature outside the star. In GR curvature drops to zero on star surface where ρ = p = 0. In the model underconsideration the scalar curvature dumps more slowly in comparison with vacuum R2 gravity due to axion ‘galo’ around the star.

scholarly journals Characterizing exo-ring systems around fast-rotating stars using the Rossiter–McLaughlin effect

2017 ◽  
Vol 472 (3) ◽  
pp. 2713-2721 ◽  
Author(s):  
Ernst J.W. de Mooij ◽  
Christopher A. Watson ◽  
Matthew A. Kenworthy
Keyword(s):  
Rotating Stars ◽  
Ring Systems ◽  
Fast Rotating

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 Neutron stars as probes of dark matter

2020 ◽  
Vol 29 (14) ◽  
pp. 2043028
Author(s):  
M. Ángeles Pérez-García ◽  
Joseph Silk
Keyword(s):  
General Relativity ◽  
Dark Matter ◽  
Equation Of State ◽  
Neutron Stars ◽  
Internal Structure ◽  
Stellar Objects ◽  
Ordinary Matter ◽  
Stable Solutions ◽  
The Universe

Neutron Stars (NSs) are compact stellar objects that are stable solutions in General Relativity. Their internal structure is usually described using an equation of state that involves the presence of ordinary matter and its interactions. However there is now a large consensus that an elusive sector of matter in the universe, described as dark matter, remains as yet undiscovered. In such a case, NSs should contain both, baryonic and dark matter. We argue that depending on the nature of the dark matter and in certain circumstances, the two matter components would form a mixture inside NSs that could trigger further changes, some of them observable. The very existence of NSs constrains the nature and interactions of dark matter in the universe.

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