ANALYSIS OF THE EQUATIONS OF STATE FOR NEUTRON STARS

2020 ◽  
Vol 5 (333) ◽  
pp. 43-52
Author(s):  
A. Tlemissov ◽  
◽  
Zh. Tlemissova ◽  
K. Boshkayev ◽  
A. Urazalina ◽  
...  
Keyword(s):  
Equation Of State ◽  
Equations Of State ◽  
Dense Matter ◽  
Nucleon Nucleon ◽  
Particle Methods ◽  
Central Density ◽  
Density Radius ◽  
Nucleon Nucleon Interaction ◽  
The Difference ◽  
Principle Of Causality

In this work we consider various equations of state of neutron star matter, which include from the point of neutron drops formation to supra nuclear densities. Particular attention is paid to the nucleon – nucleon interaction since, in addition to the kinetic energies of the particles, the interactions among nucleons play a key role. Moreover, we investigate the properties of super-dense matter with diverse sets of particles such as electrons, protons, and the contribution of various particles-carriers of interaction. In order to achieve these goals, different potentials were considered, which are in a good agreement with experimental data. Furthermore, we find the energy of the system by using a variety of multi-particle methods, including the interaction of nucleons. Thanks to this information, thermodynamic parameters such as pressure, energy density and the speed of sound in the star are calculated. We compared similar equations of state of matter so that we could demonstrate the difference from each other. The Tolman-Oppenheimer-Volkoff system of equations has been solved numerically to construct mass-central density, radius-central density and mass-radius relations using different equations of state. In conclusion, the latest observational constraints on the equation of state are taken into account and we show that the observational data require that the equation of state be stiff, despite the fact that all stiff equations of state violate the principle of causality at high central densities, unlike soft ones.

EQUATION OF STATE OF ASYMMETRIC NUCLEAR MATTER WITH GOGNY AND COULOMB INTERACTIONS

1990 ◽  
Vol 05 (14) ◽  
pp. 1071-1080 ◽  
Author(s):  
S. W. HUANG ◽  
M. Z. FU ◽  
S. S. WU ◽  
S. D. YANG
Keyword(s):  
Equation Of State ◽  
Nuclear Matter ◽  
Coulomb Interaction ◽  
Chemical Potential ◽  
Compression Modulus ◽  
Nucleon Nucleon ◽  
Effective Density ◽  
Coulomb Interactions ◽  
Asymmetric Nuclear Matter ◽  
Nucleon Nucleon Interaction

The equation of state of the asymmetric nuclear matter is calculated with the Gogny D1 effective density-dependent nucleon-nucleon interaction and the Coulomb interaction in the framework of the finite-temperature HF method with the rearrangement term. The dependence of the thermodynamical properties such as the critical temperature of the liquid-gas phase transition, the chemical potential, the compression modulus and the entropy on the Coulomb interaction in nuclear matter is treated by using a shielded two-body Coulomb potential and this method has been found to be a reasonable and effective approach.

EQUATION OF STATE OF HOT NUCLEAR AND NEUTRON MATTER: A STATISTICAL APPROACH

2006 ◽  
Vol 15 (05) ◽  
pp. 1127-1139 ◽  
Author(s):  
H. R. MOSHFEGH
Keyword(s):  
Equation Of State ◽  
Nucleon Nucleon ◽  
Neutron Matter ◽  
Effect Of Temperature ◽  
Variational Parameter ◽  
Experimental Prediction ◽  
Matter System ◽  
Nucleon Nucleon Interaction ◽  
Theoretical Results ◽  
Good Agreement

The symmetric nuclear and neutron matter equation of state at finite temperature are calculated in the frame of the Thomas-Fermi approximation using the effective nucleon-nucleon interaction of Myers and Swiatecki. By introducing an effective mass in distribution function as a variational parameter, the effect of temperature on pressure, entropy, specific heat capacity, incompressibility and binding energy is discussed. A critical temperature of 17.2 MeV and a critical exponent of 0.32 for symmetric nuclear matter is found and we find that there is no phase transition in the neutron matter system. The results of calculations are in good agreement with experimental prediction and other theoretical results.

scholarly journals Thermal properties of hot and dense matter: Influence of rapid rotation on protoneutron stars, hot neutron stars, and neutron star merger remnants

2021 ◽  
Vol 252 ◽  
pp. 05004
Author(s):  
Polychronis Koliogiannis ◽  
Charalampos Moustakidis
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Neutron Stars ◽  
Nuclear Matter ◽  
Equations Of State ◽  
Interaction Model ◽  
Dense Matter ◽  
Baryon Density ◽  
Dense Nuclear Matter ◽  
Protoneutron Stars

The knowledge of the equation of state is a key ingredient for many dynamical phenomena that depend sensitively on the hot and dense nuclear matter, such as the formation of protoneutron stars and hot neutron stars. In order to accurately describe them, we construct equations of state at FInite temperature and entropy per baryon for matter with varying proton fractions. This procedure is based on the momentum dependent interaction model and state-of-the-art microscopic data. In addition, we investigate the role of thermal and rotation effects on microscopic and macroscopic properties of neutron stars, including the mass and radius, the frequency, the Kerr parameter, the central baryon density, etc. The latter is also connected to the hot and rapidly rotating remnant after neutron star merger. The interplay between these quantities and data from late observations of neutron stars, both isolated and in matter of merging, could provide useful insight and robust constraints on the equation of state of nuclear matter.

scholarly journals Hyperons in hot dense matter: what do the constraints tell us for equation of state?

2018 ◽  
Vol 35 ◽  
Author(s):  
M. Fortin ◽  
M. Oertel ◽  
C. Providência
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Symmetry Energy ◽  
Nuclear Physics ◽  
Equations Of State ◽  
Dense Matter ◽  
Baryon Octet ◽  
Thermodynamic Quantities ◽  
Binary Neutron Star ◽  
Hot Matter

AbstractFor core-collapse and neutron star merger simulations, it is important to have adequate equations of state which describe dense and hot matter as realistically as possible. We present two newly constructed equations of state including the entire baryon octet, compatible with the main constraints coming from nuclear physics, both experimental and theoretical. One of the equations of state describes cold β-equilibrated neutron stars with a maximum mass of 2 Msun. Results obtained with the new equations of state are compared with the ones of DD2Y, the only existing equation of state containing the baryon octet and satisfying the above constraints. The main difference between our new equations of state and DD2Y is the harder symmetry energy of the latter. We show that the density dependence of the symmetry energy has a direct influence on the amount of strangeness inside hot and dense matter and, consequently, on thermodynamic quantities. We expect that these differences affect the evolution of a proto-neutron star or binary neutron star mergers. We propose also several parameterisations based on the DD2 and SFHo models calibrated to Lambda hypernuclei that satisfy the different constraints.

scholarly journals Neural network reconstruction of the dense matter equation of state derived from the parameters of neutron stars

2020 ◽  
Vol 642 ◽  
pp. A78 ◽  
Author(s):  
F. Morawski ◽  
M. Bejger
Keyword(s):  
Neural Network ◽  
Machine Learning ◽  
Neural Networks ◽  
Neutron Star ◽  
Equation Of State ◽  
Neutron Stars ◽  
Equations Of State ◽  
Dense Matter ◽  
Data Set ◽  
Global Parameters

Context. Neutron stars are currently studied with an rising number of electromagnetic and gravitational-wave observations, which will ultimately allow us to constrain the dense matter equation of state and understand the physical processes at work within these compact objects. Neutron star global parameters, such as the mass and radius, can be used to obtain the equation of state by directly inverting the Tolman-Oppenheimer-Volkoff equations. Here, we investigate an alternative approach to this procedure. Aims. The aim of this work is to study the application of the artificial neural networks guided by the autoencoder architecture as a method for precisely reconstructing the neutron star equation of state, using their observable parameters: masses, radii, and tidal deformabilities. In addition, we study how well the neutron star radius can be reconstructed using only the gravitational-wave observations of tidal deformability, that is, using quantities that are not related in any straightforward way. Methods. The application of an artificial neural network in the equation-of-state reconstruction exploits the non-linear potential of this machine learning model. Since each neuron in the network is basically a non-linear function, it is possible to create a complex mapping between the input sets of observations and the output equation-of-state table. Within the supervised training paradigm, we construct a few hidden-layer deep neural networks on a generated data set, consisting of a realistic equation of state for the neutron star crust connected with a piecewise relativistic polytropes dense core, with its parameters representative of state-of-the art realistic equations of state. Results. We demonstrate the performance of our machine-learning implementation with respect to the simulated cases with a varying number of observations and measurement uncertainties. Furthermore, we study the impact of the neutron star mass distributions on the results. Finally, we test the reconstruction of the equation of state trained on parametric polytropic training set using the simulated mass–radius and mass–tidal-deformability sequences based on realistic equations of state. Neural networks trained with a limited data set are capable of generalising the mapping between global parameters and equation-of-state input tables for realistic models.

scholarly journals MAXIMUM MASS OF A CLASS OF COLD COMPACT STARS

2006 ◽  
Vol 15 (03) ◽  
pp. 405-418 ◽  
Author(s):  
R. SHARMA ◽  
S. KARMAKAR ◽  
S. MUKHERJEE
Keyword(s):  
Equation Of State ◽  
Boundary Conditions ◽  
Prior Knowledge ◽  
Surface Density ◽  
Equations Of State ◽  
Compact Stars ◽  
Central Density ◽  
Maximum Mass ◽  
Simple Method ◽  
Tov Equation

We calculate the maximum mass of the class of compact stars described by the Vaidya–Tikekar27 model. The model permits a simple method of systematically fixing bounds on the maximum possible mass of cold compact stars with a given value of radius or central density or surface density. The relevant equations of state are also determined. Although simple, the model is capable of describing the general features of the recently observed very compact stars. For the calculation, no prior knowledge of the equation of state (EOS) is required. This is in contrast to earlier calculations for maximum mass which were done by choosing first the relevant EOSs and using those to solve the TOV equation with appropriate boundary conditions. The bounds obtained by us are comparable and, in some cases, more restrictive than the earlier results.

scholarly journals Equations of State in Stellar Structure and Evolution

1994 ◽  
Vol 147 ◽  
pp. 1-15
Author(s):  
H. M. Van Horn
Keyword(s):  
Phase Transition ◽  
Equation Of State ◽  
White Dwarfs ◽  
Equations Of State ◽  
Dense Matter ◽  
Reaction Rates ◽  
Stellar Structure ◽  
First Order ◽  
First Order Phase Transition ◽  
First Order Phase

AbstractIn this paper I summarize some of the recent advances in studies of dense matter. Research on phase separation in the binary ionic mixtures (BIMs) that constitute the matter in white dwarfs has been motivated by the need to obtain accurate estimates for the ages of the faintest white dwarfs and thus of the disk of our Galaxy. Substantial age increases appear possible, but it is not yet clear whether such large increases occur in real white dwarfs. A second advance is the prediction, based on state-of-the-art physical calculations, that ionization of H at low temperatures and increasing densities may occur via a first-order “plasma phase transition” (PPT). Astrophysical consequences of this result are still being explored in an effort to test this prediction. Related to these equation-of-state calculations are calculations of the enhancement of nuclear reaction rates at high densities. New thermonuclear rates have been computed for C+C reactions in BIMs, although there is currently some controversy about results at the highest densities. New pycnonuclear reaction rates have also been calculated for BIMs, and it has been suggested that He-burning at T = 0 may occur through a first-order phase transition. Finally, calculations of the equation of state of matter in strong magnetic fields and of radiative opacities at high densities have undergone very recent and substantial improvements, which are just beginning to be utilized in astrophysical calculations.

scholarly journals Unified description of dense matter in neutron stars and magnetars

2012 ◽  
Vol 8 (S291) ◽  
pp. 359-361
Author(s):  
N. Chamel ◽  
R. L. Pavlov ◽  
L. M. Mihailov ◽  
Ch. J. Velchev ◽  
Zh. K. Stoyanov ◽  
...  
Keyword(s):  
Neutron Stars ◽  
Density Functional ◽  
Nuclear Energy ◽  
Equations Of State ◽  
Dense Matter ◽  
Nucleon Nucleon ◽  
Many Body ◽  
Energy Density Functional ◽  
Functional Theory ◽  
Unified Description

AbstractWe have recently developed a set of equations of state based on the nuclear energy density functional theory providing a unified description of the different regions constituting the interior of neutron stars and magnetars. The nuclear functionals, which were constructed from generalized Skyrme effective nucleon-nucleon interactions, yield not only an excellent fit to essentially all experimental atomic mass data but were also constrained to reproduce the neutron-matter equation of state as obtained from realistic many-body calculations.

scholarly journals Nuclear matter equation of state from a quark-model nucleon-nucleon interaction

2015 ◽  
Vol 92 (6) ◽  
Author(s):  
K. Fukukawa ◽  
M. Baldo ◽  
G. F. Burgio ◽  
L. Lo Monaco ◽  
H.-J. Schulze
Keyword(s):  
Equation Of State ◽  
Nuclear Matter ◽  
Quark Model ◽  
Nucleon Nucleon ◽  
Nucleon Interaction ◽  
Nucleon Nucleon Interaction

MICROSCOPIC STUDY OF THE EFFECT OF HEXADECAPOLE DEFORMATION ON BOTH FUSION CROSS-SECTION AND BARRIER DISTRIBUTION

2000 ◽  
Vol 15 (38n39) ◽  
pp. 2315-2326 ◽  
Author(s):  
M. ISMAIL ◽  
A. SH. GHAZAL
Keyword(s):  
Cross Section ◽  
Fusion Cross Section ◽  
Heavy Ion ◽  
Nucleon Nucleon ◽  
Finite Range ◽  
Zero Range ◽  
Barrier Distribution ◽  
Nucleon Nucleon Interaction ◽  
The Difference ◽  
Double Folding

The interaction potential for deformed-spherical nuclear pair is derived microscopically in the framework of double folding model with M3Y-Paris nucleon–nucleon interaction. The heavy target nucleus 238 U together with the light projectile nucleus 16 O are considered as an example. The exchange part of the heavy ion (HI) potential has been calculated using finite-range exchange NN force instead of the zero-range pseudoforce. Neutron thickness and the difference in kinetic energy densities between neutrons and protons have been taken into consideration in calculating the exchange HI potential. For this pair the fusion cross-section as well as the barrier distribution are calculated. These calculations have been done using three different values of hexadecapole deformation parameter of 238 U . The effect of using both the finite-range exchange NN force and the hexadecapole deformation on the fusion cross-section and the barrier distribution have been discussed.

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