scholarly journals Speed of sound constraints on maximally-rotating neutron stars

2020 ◽  
Vol 27 ◽  
pp. 155
Author(s):  
Chrysovalantis Margaritis ◽  
Polychronis Koliogiannis Koutmiridis ◽  
Charalampos Moustakidis
Keyword(s):  
Neutron Stars ◽  
Speed Of Sound ◽  
Sound Speed ◽  
Transition Density ◽  
Dense Matter ◽  
Mass Region ◽  
Upper Bounds ◽  
Theoretical Treatment ◽  
Maximum Mass ◽  
Bulk Properties

In the present work we provide a theoretical treatment concerning the effects of the upper bound of the sound speed in dense matter on the bulk properties of maximally-rotating (at mass-shedding limit) neutron stars. We investigate to what extent the possible predicted (from various theories and conjectures) upper bounds on the speed of sound constrain various key quantities, such as the maximum mass and the corresponding radius, Keplerian frequency, Kerr parameter and moment of inertia. We mainly focus on the lower proposed limit, , and we explore in which mass region a rotating neutron star collapses to a black hole. In any case, useful relations of the mentioned bulk properties with the transition density are derived and compared with the corresponding non-rotating cases.

scholarly journals Locating the special point of hybrid neutron stars

2022 ◽  
Vol 258 ◽  
pp. 07009
Author(s):  
Mateusz Cierniak ◽  
David Blaschke
Keyword(s):  
Neutron Stars ◽  
Sound Speed ◽  
Transition Density ◽  
Mass Range ◽  
Special Point ◽  
Model Parameters ◽  
Maximum Mass ◽  
Upper Limit ◽  
Pressure Scale ◽  
Hybrid Stars

The special point is a feature unique to models of hybrid neutron stars. It represents a location on their mass–radius sequences that is insensitive to the phase transition density. We consider hybrid neutron stars with a core of deconfined quark matter that obeys a constant–sound–speed (CSS) equation of state model and provide a fit formula for the coordinates of the special point as functions of the squared sound speed (cs2) and pressure scale (A) parameters. Using the special point mass as a proxy for the maximum mass of the hybrid stars we derive limits for the CSS model parameters based on the recent NICER constraint on mass and radius of pulsar PSR J0740+6620, 0.36 < Cs min2 < 0.43 and 80 < A[MeV/fm3] < 160. The upper limit for the maximum mass of hybrid stars depends on the upper limit for cs2 so that choosing cs,max2 = 0.6 results in Mmax < 2.7 M⊙, within the mass range of GW190814.

scholarly journals Speed of sound and quark confinement inside neutron stars

2020 ◽  
Vol 229 (22-23) ◽  
pp. 3651-3661
Author(s):  
Michał Marczenko
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Neutron Stars ◽  
Speed Of Sound ◽  
Dense Matter ◽  
High Mass ◽  
Quark Confinement ◽  
Binary Neutron Star ◽  
Upper Limit ◽  
Unified Description

AbstractSeveral observations of high-mass neutron stars (NSs), as well as the first historic detection of the binary neutron star merger GW170817, have delivered stringent constraints on the equation of state (EoS) of cold and dense matter. Recent studies suggest that, in order to simultaneously accommodate a 2M⊙ NS and the upper limit on the compactness, the pressure has to swiftly increase with density and the corresponding speed of sound likely exceeds the conformal limit. In this work, we employ a unified description of hadron-quark matter, the hybrid quark-meson-nucleon (QMN) model, to investigate the EoS under NS conditions. We show that the dynamical confining mechanism of the model plays an important role in explaining the observed properties of NSs.

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 &gt; 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 &gt; 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 &gt; 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 &gt; 1.40 if ρs &gt; 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 Phase transitions in dense matter and the maximum mass of neutron stars

2013 ◽  
Vol 553 ◽  
pp. A22 ◽  
Author(s):  
N. Chamel ◽  
A. F. Fantina ◽  
J. M. Pearson ◽  
S. Goriely
Keyword(s):  
Phase Transitions ◽  
Neutron Stars ◽  
Dense Matter ◽  
Maximum Mass

scholarly journals Protoneutron stars and neutron stars

2000 ◽  
Vol 177 ◽  
pp. 663-664
Author(s):  
D. Gondek-Rosińska ◽  
P. Haensel ◽  
J. L. Zdunik
Keyword(s):  
Equation Of State ◽  
Neutron Stars ◽  
Dense Matter ◽  
Early Evolution ◽  
Maximum Mass ◽  
Standard Equation ◽  
Nuclear Incompressibility ◽  
Protoneutron Stars ◽  
Protoneutron Star

AbstractWe find constraints on minimum and maximum mass of ordinary neutron stars imposed by their early evolution (protoneutron star stage). We calculate models of protoneutron stars using a realistic standard equation of state of hot, dense matter valid for both supranuclear and subnuclear densities. Results for different values of the nuclear incompressibility are presented.

scholarly journals QCD equations of state and speed of sound in neutron stars

2021 ◽  
Vol 31 (1) ◽  
Author(s):  
Toru Kojo
Keyword(s):  
Phase Transitions ◽  
Neutron Star ◽  
Neutron Stars ◽  
Quantum Chromodynamics ◽  
Speed Of Sound ◽  
Equations Of State ◽  
Dense Matter ◽  
Solar Mass ◽  
Short Article ◽  
Hadron Physics

AbstractNeutron stars are cosmic laboratories to study dense matter in quantum chromodynamics (QCD). The observable mass-radius relations of neutron stars are determined by QCD equations of state and can reflect the properties of QCD phase transitions. In the last decade, there have been historical discoveries in neutron stars; the discoveries of two-solar mass neutron stars and neutron star merger events, which have imposed tight constraints on equations of state. While a number of equations of state are constructed to satisfy these constraints, a theoretical challenge is how to reconcile those constructions with the microphysics expected from the hadron physics and in-medium calculations. In this short article, we briefly go over recent observations and discuss their implications for dense QCD matter, referring to QCD constraints in the low- and high-density limits, QCD-like theories, and lattice QCD results for baryon-baryon interactions.

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