compact stars
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Author(s):  
Luca Baiotti

AbstractI review the current global status of research on gravitational waves emitted from mergers of binary neutron star systems, focusing on general-relativistic simulations and their use to interpret data from the gravitational-wave detectors, especially in relation to the equation of state of compact stars.


Universe ◽  
2022 ◽  
Vol 8 (1) ◽  
pp. 34
Author(s):  
José C. Jiménez ◽  
Eduardo S. Fraga

We investigated compact stars consisting of cold quark matter and fermionic dark matter treated as two admixed fluids. We computed the stellar structures and fundamental radial oscillation frequencies of different masses of the dark fermion in the cases of weak and strong self-interacting dark matter. We found that the fundamental frequency can be dramatically modified and, in some cases, stable dark strange planets and dark strangelets with very low masses and radii can be formed.


2022 ◽  
Vol 82 (1) ◽  
Author(s):  
Jay Solanki ◽  
Jackson Levi Said

AbstractIn this paper, we develop a new class of analytical solutions describing anisotropic stellar structures of observed neutron stars using modified f(T) gravity. We use the off-diagonal tetrad that is best suitable for studying spherically symmetric objects in f(T) gravity. We develop exact solutions in the quadratic model of f(T) gravity by introducing physically reliable metric potentials that can describe a wide range of astrophysical systems. We then apply the model to investigate the stellar structures of four observed compact stars, 4U 1538-52, J0437-4715, J0030+0451, and 4U 1820-30. We calculate the values of model parameters for the stellar objects under examination in this paper. Comprehensive graphical analysis shows that the model describing anisotropic stellar structures is physically acceptable, causal, and stable. The model inherently exhibits the quadratic equation of state that can be utilized to investigate the material composition and stellar structures of the observed compact stars.


2021 ◽  
Author(s):  
Abdelghani Errehymy ◽  
G. Mustafa ◽  
Youssef Khedif ◽  
Mohammed Daoud

Abstract The main aim of this manuscript is to explore the existence and salient features of spherically symmetric relativistic quark stars in the background of massive Brans-Dicke gravity. The exact solutions to the modified Einstein field equations are derived for specific forms of coupling and scalar field functions by using the equation of state relating to the strange quark matter that stimulates the phenomenological MIT-Bag model as a free Fermi gas of quarks. We use a well-behaved function along with Karmarkar condition for class-one embedding as well as junction conditions to determine the unknown metric tensors. The radii of the strange compact stars viz., PSR J1416-2230, PSR J1903+327, 4U 1820-30, CenX-3, EXO1785-248 are predicted via their observed mass for different values of the massive Brans-Dicke parameters. We explore the influences of mass of scalar field $m_{\phi}$ as well as coupling parameter $\omega_{BD}$ along with bag constant $\mathcal{B}$ on state determinants and perform several tests on the viability and stability of the constructed stellar model. Conclusively, we find that our stellar system is physically viable and stable as it satisfies all the energy conditions as well as necessary stability criteria under the influence of a gravitational scalar field.


Author(s):  
Adnan Malik ◽  
Iftikhar Ahmad ◽  
Kiran

In this paper, we investigate the behavior of anisotropic compact stars in generalized modified gravity, namely [Formula: see text] gravity, where [Formula: see text] represents the Ricci scalar, [Formula: see text] is the scalar potential function and [Formula: see text] is a kinetic term of [Formula: see text]. We consider the spherically symmetric spacetime to analyze the feasible exposure of compact stars. We observe the behavior of anisotropic compact stars which includes Her X1, SAX J 1808.4-3658 and 4U 1820-30. From the graphical evaluation of energy density, tangential pressure, radial pressure, equilibrium conditions, energy conditions, mass–radius relationship, compactness and stability analysis of compact stars, it is concluded that the behavior of candidates of compact stars is regular in [Formula: see text] gravity for the considered parameter.


Author(s):  
Jay Solanki

In this paper, model of gravitational collapse of anisotropic compact stars in a new theory of [Formula: see text] gravity has been developed. The author considers the modified gravity model of [Formula: see text] to investigate a physically acceptable model of gravitational collapse of anisotropic compact stars. First, the author presents a brief review of the development of field equations of gravitational collapse in [Formula: see text] gravity for a particular interior metric for compact stars. Then analytical solutions for various physical quantities of collapsing anisotropic compact stars in [Formula: see text] gravity have been developed. By analyzing plots of various physical parameters and conditions, it is shown that the model is physically acceptable for describing the gravitational collapse of anisotropic compact stars in [Formula: see text] gravity.


2021 ◽  
Author(s):  
SiNa Wei ◽  
Zhaoqing Feng

Abstract With the two-fluid TOV equation, the properties of dark matter (DM) admixed NSs (DANSs) have been studied. Different from previous studies, we found that increase of the maximum mass and decrease of the radius of 1.4 $M_\odot$ can occur simultaneously in DANS. This stems from the fact that the equation of state (EOS) of DM can be very soft at low density but very stiff at high density. It is well known that the IU-FSU and XS models can not reproduce the neutron star (NS) with a maximum mass greater than 2.0 $M_\odot$. However, considering IU-FSU and XS models in DANS, there are always mass and interactions of DM that can reproduce a maximum mass greater than 2.0 $M_\odot$ and the radius of 1.4 $M_\odot$ below 13.7km. The difference of DANS between the DM with chiral symmetry (DMC) and the DM with meson exchange (DMM) becomes obvious when the central energy density ratio of the DM is greater than one of the NM. When the central energy density ratio of the DM is greater than one of the NM, the DMC model with the DM mass of 1000 MeV still can reproduce a maximum mass greater than 2.0 $M_\odot$ and the radius of 1.4 $M_\odot$ below 13.7km. In the same case, although the maximum mass of DANS with the DMM model is greater than 2.0 $M_\odot$ , the radius of 1.4 $M_\odot$ with the DMM model will surpass 13.7km obviously. \com{In two-fluid system, it is worth noting that the maximum mass of DANS can be larger than 3.0 $M_\odot$. As a consequence, the dimensionless tidal deformability $\Lambda_{CP}$ of DANS with 1.4 $M_\odot$, which increase with increasing the maximum mass of DANS, could be larger than 800 when the radius of DANS with 1.4 $M_\odot$ is about 13.0km.}


2021 ◽  
Vol 21 (10) ◽  
pp. 250
Author(s):  
Xiao-Yu Lai ◽  
Cheng-Jun Xia ◽  
Yun-Wei Yu ◽  
Ren-Xin Xu

Abstract The state of supranuclear matter in compact stars remains puzzling, and it is argued that pulsars could be strangeon stars. The consequences of merging double strangeon stars are worth exploring, especially in the new era of multi-messenger astronomy. To develop the “strangeon kilonova” scenario proposed in Paper I, we make a qualitative description about the evolution of ejecta and light curves for merging double strangeon stars. In the hot environment of the merger, the strangeon nuggets ejected by tidal disruption and hydrodynamical squeezing would suffer from evaporation, in which process particles, such as strangeons, neutrons and protons, are emitted. Taking into account both the evaporation of strangeon nuggets and the decay of strangeons, most of the strangeon nuggets would turn into neutrons and protons, within dozens of milliseconds after being ejected. The evaporation rates of different particles depend on temperature, and we find that the ejecta could end up with two components, with high and low opacity respectively. The high opacity component would be in the directions around the equatorial plane, and the low opacity component would be in a broad range of angular directions. The bolometric light curves show that the spin-down power of the long-lived remnant would account for the whole emission of kilonova AT2017gfo associated with GW170817, if the total ejected mass ∼ 10−3 M ⊙. The detailed picture of merging double strangeon stars is expected to be tested by future numerical simulations.


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