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 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 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.

Strange quark mass effect on the structure of hybrid stars

2018 ◽  
Vol 27 (01) ◽  
pp. 1850006 ◽  
Author(s):  
Jian-Feng Xu ◽  
Yan-An Luo ◽  
Lei Li ◽  
Guang-Xiong Peng
Keyword(s):  
Quark Matter ◽  
Quark Mass ◽  
Strange Quark ◽  
Mass Effect ◽  
Compact Stars ◽  
Model Parameters ◽  
Maximum Mass ◽  
Strange Quark Mass ◽  
Wide Range ◽  
Hybrid Stars

We study the strange quark mass effect on the phase diagram of strong interaction and the structure of compact stars with a thermodynamically enhanced perturbative QCD model by matching quark matter onto nuclear matter using the Gibbs conditions. It is found that the mass effect of strange quark matter can obviously stiffen the equation of state of mixed phases and result in more massive hybrid stars (HSs), while that usually lowers the maximum mass of pure quark stars. Given reasonable model parameters, the maximum mass of HSs can reach two times the solar mass and the stars always have mixed-phase core in a considerably wide range of model parameters.

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 Simplified Thermal Evolution of Proto-Hybrid Stars

2017 ◽  
Vol 45 ◽  
pp. 1760041 ◽  
Author(s):  
Mauro Mariani ◽  
Milva Orsaria ◽  
Héctor Vucetich
Keyword(s):  
Phase Transition ◽  
Neutron Stars ◽  
Thermal Evolution ◽  
Late Phase ◽  
Hadronic Matter ◽  
Maximum Mass ◽  
Hybrid Star ◽  
Star Evolution ◽  
Hybrid Stars ◽  
Quark Phase

We study the possibility of a hadron-quark phase transition in the interior of neutron stars, taking into account different schematic evolutionary stages at finite temperature. Furthermore, we analyze the astrophysical properties of hot and cold hybrid stars, considering the constraint on maximum mass given by the pulsars J1614-2230 and J1614-2230. We obtain cold hybrid stars with maximum masses [Formula: see text] M[Formula: see text]. Our study also suggest that during the proto-hybrid star evolution a late phase transition between hadronic matter and quark matter could occur, in contrast with previous studies of proto-neutron stars.

scholarly journals On the red supergiant problem

2020 ◽  
Vol 493 (4) ◽  
pp. 4945-4949 ◽  
Author(s):  
C S Kochanek
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Bayesian Approach ◽  
Mass Range ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Maximum Mass ◽  
Upper Limit

ABSTRACT We examine the problem of estimating the mass range corresponding to the observed red supergiant (RSG) progenitors of Type IIP supernovae. Using Monte Carlo simulations designed to reproduce the properties of the observations, we find that the approach of Davies & Beasor significantly overestimates the maximum mass, yielding an upper limit of Mh/M⊙ = 20.5 ± 2.6 for an input population with Mh/M⊙ = 18. Our preferred Bayesian approach does better, with Mh/M⊙ = 18.6 ± 2.1 for the same input populations, but also tends to overestimate Mh. For the actual progenitor sample and a Salpeter initial mass function, we find $M_{\rm h}/\mathrm{M}_\odot = 19.01_{-2.04}^{+4.04}$ for the Eldridge & Tout mass–luminosity relation used by Smartt and Davies & Beasor, and $M_{\rm h}/\mathrm{M}_\odot = 21.28_{-2.28}^{+4.52}$ for the Sukhbold, Woosley & Heger mass–luminosity relation. Based on the Monte Carlo simulations, we estimate that these are overestimated by $(3.3\pm 0.8)\, \mathrm{M}_\odot$. The red supergiant problem remains.

scholarly journals THE UNIFICATION OF RELATIVISTIC JETS

2014 ◽  
Vol 28 ◽  
pp. 1460188 ◽  
Author(s):  
LUIGI FOSCHINI
Keyword(s):  
Black Holes ◽  
Neutron Stars ◽  
Mass Range ◽  
Supermassive Black Holes ◽  
Compact Objects ◽  
Relativistic Jets

I report about the unification of relativistic jets from compact objects. The mass range is between 1.4 and 10 billion solar masses (i.e. from neutron stars to supermassive black holes in galaxies).

scholarly journals The dark matter interpretation of the 3.5-keV line is inconsistent with blank-sky observations

Science ◽  
2020 ◽  
Vol 367 (6485) ◽  
pp. 1465-1467 ◽  
Author(s):  
Christopher Dessert ◽  
Nicholas L. Rodd ◽  
Benjamin R. Safdi
Keyword(s):  
Dark Matter ◽  
Emission Line ◽  
Decay Rate ◽  
Milky Way ◽  
Line Emission ◽  
Mass Range ◽  
Sterile Neutrinos ◽  
X Ray ◽  
Upper Limit ◽  
Nearby Galaxies

Observations of nearby galaxies and galaxy clusters have reported an unexpected x-ray emission line around 3.5 kilo–electron volts (keV). Proposals to explain this line include decaying dark matter—in particular, that the decay of sterile neutrinos with a mass around 7 keV could match the available data. If this interpretation is correct, the 3.5-keV line should also be emitted by dark matter in the halo of the Milky Way. We used more than 30 megaseconds of XMM-Newton (X-ray Multi-Mirror Mission) blank-sky observations to test this hypothesis, finding no evidence of the 3.5-keV line emission from the Milky Way halo. We set an upper limit on the decay rate of dark matter in this mass range, which is inconsistent with the possibility that the 3.5-keV line originates from dark matter decay.

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