scholarly journals What if the neutron star maximum mass is beyond ∼2.3 M⊙?

2020 ◽  
Vol 499 (3) ◽  
pp. 4526-4533
Author(s):  
X H Wu ◽  
S Du ◽  
R X Xu
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Transition Density ◽  
Compact Stars ◽  
Maximum Mass ◽  
Polytropic Model ◽  
Merger Event ◽  
Strong Bound ◽  
Two Parameters ◽  
Polytropic Exponent

ABSTRACT By assuming the formation of a black hole soon after the merger event of GW170817, the maximum mass of non-rotating stable neutron star, MTOV ≃ 2.3 M⊙, is proposed by numerical relativity, but there is no solid evidence to rule out MTOV > 2.3 M⊙ from the point of both microphysical and astrophysical views. It is naturally expected that the equation of state (EOS) would become stiffer beyond a specific density to explain massive pulsars. We consider the possibility of EOSs with MTOV > 2.3 M⊙, investigating the stiffness and the transition density in a polytropic model, for two kinds of neutron stars (i.e. gravity-bound and strong-bound stars on surface). Only two parameters are input in both cases: (ρt, γ) for gravity-bound neutron stars, while (ρs, γ) for strong-bound strange stars, with ρt the transition density, ρs the surface density, and γ the polytropic exponent. In the matter of MTOV > 2.3 M⊙ for the maximum mass and 70 ≤ Λ1.4 ≤ 580 for the tidal deformability, it is found that the smallest ρt and γ should be ∼0.50 ρ0 and ∼2.65 for neutron stars, respectively, whereas for strange star, we have γ > 1.40 if ρs > 1.0 ρ0 (ρ0 is the nuclear saturation density). These parametric results could guide further research of the real EOS with any foundation of microphysics if a pulsar mass higher than 2.3 M⊙ is measured in the future, especially for an essential comparison of allowed parameter space between gravity-bound and strong-bound 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 Astrophysical implications of neutron star inspiral and coalescence

2020 ◽  
Vol 29 (11) ◽  
pp. 2041015
Author(s):  
John L. Friedman ◽  
Nikolaos Stergioulas
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Neutron Stars ◽  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Maximum Mass ◽  
X Ray ◽  
Spectral Bands ◽  
Heaviest Elements ◽  
X Ray Binaries

The first inspiral of two neutron stars observed in gravitational waves was remarkably close, allowing the kind of simultaneous gravitational wave and electromagnetic observation that had not been expected for several years. Their merger, followed by a gamma-ray burst and a kilonova, was observed across the spectral bands of electromagnetic telescopes. These GW and electromagnetic observations have led to dramatic advances in understanding short gamma-ray bursts; determining the origin of the heaviest elements; and determining the maximum mass of neutron stars. From the imprint of tides on the gravitational waveforms and from observations of X-ray binaries, one can extract the radius and deformability of inspiraling neutron stars. Together, the radius, maximum mass, and causality constrain the neutron-star equation of state, and future constraints can come from observations of post-merger oscillations. We selectively review these results, filling in some of the physics with derivations and estimates.

scholarly journals Constraints on the inner edge of neutron star crusts from relativistic nuclear energy density functionals

2019 ◽  
Vol 18 ◽  
pp. 107
Author(s):  
Ch. C. Moustakidis ◽  
T. Niksic ◽  
G. A. Lalazissis ◽  
D. Vretenar ◽  
P. Ring
Keyword(s):  
Neutron Star ◽  
Energy Density ◽  
Neutron Stars ◽  
Nuclear Energy ◽  
Liquid Core ◽  
Transition Density ◽  
Binding Energies ◽  
Density Functionals ◽  
The Core ◽  
Finite Nuclei

The transition density nt and pressure Pt at the inner edge between the liquid core and the solid crust of a neutron star are analyzed using the thermodynami- cal method and the framework of relativistic nuclear energy density functionals. Starting from a functional that has been carefully adjusted to experimental binding energies of finite nuclei, and varying the density dependence of the cor- responding symmetry energy within the limits determined by isovector prop- erties of finite nuclei, we estimate the constraints on the core-crust transition density and pressure of neutron stars: 0.086 fm−3 ≤ nt < 0.090 fm−3 and 0.3 MeV fm−3 < Pt ≤ 0.76 MeV fm−3 [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 The heavier the better: how to constrain mass ratios and spins of high-mass neutron star mergers

2020 ◽  
Vol 496 (1) ◽  
pp. L16-L21 ◽  
Author(s):  
Elias R Most ◽  
Lukas R Weih ◽  
Luciano Rezzolla
Keyword(s):  
Black Hole ◽  
Neutron Star ◽  
Lower Bound ◽  
Equations Of State ◽  
High Mass ◽  
Maximum Mass ◽  
Mass Ratio ◽  
Effective Spin ◽  
Binary Neutron Star ◽  
Merger Event

ABSTRACT The first binary neutron star merger event, GW170817, and its bright electromagnetic counterpart have provided a remarkable amount of information. By contrast, the second event, GW190425, with $M_{\rm tot}=3.4^{+0.3}_{-0.1}\, \mathrm{ M}_{\odot }$ and the lack of an electromagnetic counterpart, has hardly improved our understanding of neutron star physics. While GW190425 is compatible with a scenario in which the merger has led to a prompt collapse to a black hole and little ejected matter to power a counterpart, determining the mass ratio and the effective spin $\tilde{\chi }$ of the binary remains difficult. This is because gravitational waveforms cannot yet well constrain the component spins of the binary. However, since the mass of GW190425 is significantly larger than the maximum mass for non-rotating neutron stars, $M_{_{\rm TOV}}$, the mass ratio q cannot be too small, as the heavier star would not be gravitationally stable. Making use of universal relations and a large number of equations of state, we provide limits in the $(\tilde{\chi },q)$ plane for GW190425, namely qmin ≥ 0.38 and $\tilde{\chi }_{\rm max}\le 0.20$, assuming $M_\mathrm{tot} \simeq 3.4\, \mathrm{ M}_\odot$. Finally, we show how future observations of high-mass binaries can provide a lower bound on $M_{_{\rm TOV}}$.

scholarly journals Contraction of cold neutron star due to in the presence a quark core

2019 ◽  
Vol 79 (10) ◽  
Author(s):  
B. Eslam Panah ◽  
T. Yazdizadeh ◽  
G. H. Bordbar
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Quark Matter ◽  
Average Density ◽  
Dynamical Stability ◽  
Hadronic Matter ◽  
Maximum Mass ◽  
Quark Core ◽  
Hybrid Stars ◽  
Schwarzschild Radius

Abstract Motivated by importance of the existence of quark matter on structure of neutron star. For this purpose, we use a suitable equation of state (EoS) which include three different parts: (i) a layer of hadronic matter, (ii) a mixed phase of quarks and hadrons, and, (iii) a strange quark matter in the core. For this system, in order to do more investigation of the EoS, we evaluate energy, Le Chatelier’s principle and stability conditions. Our results show that the EoS satisfies these conditions. Considering this EoS, we study the effect of quark matter on the structure of neutron stars such as maximum mass and the corresponding radius, average density, compactness, Kretschmann scalar, Schwarzschild radius, gravitational redshift and dynamical stability. Also, considering the mentioned EoS in this paper, we find that the maximum mass of hybrid stars is a little smaller than that of the corresponding pure neutron star. Indeed the maximum mass of hybrid stars can be quite close to the pure neutron stars. Our calculations about the dynamical stability show that these stars are stable against the radial adiabatic infinitesimal perturbations. In addition, our analyze indicates that neutron stars are under a contraction due to the existence of quark core.

scholarly journals Neutron star structure with nuclear force mediated by hypothetical X17 boson

2021 ◽  
Vol 252 ◽  
pp. 04008
Author(s):  
Vlasios Petousis ◽  
Martin Veselský ◽  
Jozef Leja
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Neutron Stars ◽  
Nuclear Force ◽  
Nuclear Equation Of State ◽  
Upper Limit ◽  
Merger Event ◽  
Star Structure

A reported 17 MeV boson, which has been proposed as an explanation to the 8Be and 4He anomaly, is investigated in the context of its possible influence to neutron stars structure. Implementing a mX =17 MeV to the nuclear equation of state using different incompressibility values K0=245 MeV and K0=260 MeV and solving Tolman-Oppenheimer-Volkoff equations, we estimate an upper limit of MTOV ≈ 2.4M⊙ for a non rotating neutron star with span in radius R between 11.5 km to 14 km. Moving away from pure -NN with admixture of 10% protons and simulating possible softening of equation of state due to hyperons, we see that our estimated limits fit quite well inside the newest reported studies, coming from neutron stars merger event, GW190814

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 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.

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