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The Nuclear Physics of Neutron Stars
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The Nuclear Physics of Neutron Stars

A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Physics".

Deadline for manuscript submissions: closed (31 May 2024) | Viewed by 24574

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editor

Prof. Dr. Charalampos Moustakidis

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Guest Editor
Department of Nuclear and Elementaty Particle Physics, School of Physics, Faculty of Sciences, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
Interests: theoretical nuclear physics; nuclear astrophysics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Neutron stars are considered extraordinary astronomical laboratories for the physics of nuclear matter as they have the most fascinating constitution of energy and matter in the Universe. Recently, the detection of gravitational waves from the merger of two neutron stars, in a binary neutron-star system, opened a new window to explore the physics of neutron stars. In particular, the majority of the static, as well as the dynamical processes of neutron stars, are sensitively dependent on the employed equation of state. However, the knowledge of the equation of state, especially at high densities, is very uncertain and, therefore, the relevant predictions and estimations are suffering.

One of the long-standing subjects in astrophysics is the determination of the maximum mass of a neutron star (non-rotating and rotating). Neutron stars are directly related to the formation of black holes (Kerr black holes), connecting two of the most important astrophysical objects. As a consequence, the maximum neutron star mass is of great interest in studying the effect of both neutron stars and black holes on the dynamics of supernovae explosion.

Furthermore, neutron stars, due to their compactness, may rotate very fast compared to other astrophysical objects. In particular, measurement of specific properties of rapidly rotating neutron stars (including the mass and radius, frequency, moment of inertia, quadrupole moment, etc.) may lead to robust constraints on the equation of state, as well as on the constitute of nuclear matter at very high densities.

The propose of this Special Issue is to collect contributions exploring modern applications of the theory of nuclear matter in neutron stars, as well as proposed ideas to constrain the equation of state both of cold and hot nuclear matter (low/high densities) with the help of recent observations including mainly observational data form radio-pulsars, X-rays sources, gamma-ray burst sources, etc. as well as the detection of gravitational waves originating from neutron stars mergers. We wish to invite both original and review papers to this Special Issue along the lines mentioned above.

Prof. Dr. Charalampos Moustakidis
Guest Editor

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Symmetry is an international peer-reviewed open access monthly journal published by MDPI.

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Keywords

  • neutron stars
  • equation of state of nuclear matter
  • gravitational waves
  • cold and hot nuclear matter
  • binary neutron star systems
  • pulsars

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Published Papers (11 papers)

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Editorial

Jump to: Research

5 pages, 208 KiB  
Editorial
The Nuclear Physics of Neutron Stars
by Charalampos Moustakidis
Symmetry 2024, 16(6), 658; https://doi.org/10.3390/sym16060658 - 27 May 2024
Viewed by 1138
Abstract
Neutron stars are considered extraordinary astronomical laboratories for the physics of nuclear matter as they have the most fascinating constitution of energy and matter in the Universe [...] Full article
(This article belongs to the Special Issue The Nuclear Physics of Neutron Stars)

Research

Jump to: Editorial

12 pages, 271 KiB  
Article
Ghost Stars in General Relativity
by Luis Herrera, Alicia Di Prisco and Justo Ospino
Symmetry 2024, 16(5), 562; https://doi.org/10.3390/sym16050562 - 5 May 2024
Cited by 1 | Viewed by 981
Abstract
We explore an idea put forward many years ago by Zeldovich and Novikov concerning the existence of compact objects endowed with arbitrarily small mass. The energy density of such objects, which we call “ghost stars”, is negative in some regions of the fluid [...] Read more.
We explore an idea put forward many years ago by Zeldovich and Novikov concerning the existence of compact objects endowed with arbitrarily small mass. The energy density of such objects, which we call “ghost stars”, is negative in some regions of the fluid distribution, producing a vanishing total mass. Thus, the interior is matched on the boundary surface to Minkowski space–time. Some exact analytical solutions are exhibited and their properties are analyzed. Observational data that could confirm or dismiss the existence of this kind of stellar object are discussed. Full article
(This article belongs to the Special Issue The Nuclear Physics of Neutron Stars)
29 pages, 692 KiB  
Article
Nuclear Matter Properties and Neutron Star Phenomenology Using the Finite Range Simple Effective Interaction
by Xavier Viñas, Parveen Bano, Zashmir Naik and Tusar Ranjan Routray
Symmetry 2024, 16(2), 215; https://doi.org/10.3390/sym16020215 - 10 Feb 2024
Cited by 1 | Viewed by 1219
Abstract
The saturation properties of symmetric and asymmetric nuclear matter have been computed using the finite range simple effective interaction with Yukawa form factor. The results of higher-order derivatives of the energy per particle and the symmetry energy computed at saturation, namely, Q0 [...] Read more.
The saturation properties of symmetric and asymmetric nuclear matter have been computed using the finite range simple effective interaction with Yukawa form factor. The results of higher-order derivatives of the energy per particle and the symmetry energy computed at saturation, namely, Q0, Ksym, Kτ, Qsym, are compared with the corresponding values extracted from studies involving theory, experiment and astrophysical observations. The overall uncertainty in the values of these quantities, which results from a wide spectrum of studies described in earlier literature, lies in the ranges −1200≲Q0≲400 MeV, −400≲Ksym≲100 MeV, −840≲Kτ≲−126 MeV and −200≲Qsym≲800 MeV, respectively. The ability of the equations of state computed with this simple effective interaction in predicting the threshold mass for prompt collapse in binary neutron star merger and gravitational redshift has been examined in terms of the compactness of the neutron star and the incompressibility at the central density of the maximum mass star. The correlations existing between neutron star properties and the nuclear matter saturation properties have been analyzed and compared with the predictions of other model calculations. Full article
(This article belongs to the Special Issue The Nuclear Physics of Neutron Stars)
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14 pages, 395 KiB  
Article
Dense Baryonic Matter Predicted in “Pseudo-Conformal Model”
by Mannque Rho
Symmetry 2023, 15(6), 1271; https://doi.org/10.3390/sym15061271 - 16 Jun 2023
Cited by 4 | Viewed by 1048
Abstract
The World-Class University/Hanyang Project launched in Korea in 2008 led to what is now called the “pseudo-conformal model” that addresses dense compact star matter and is confronted in this short note with the presently available astrophysical observables, with focus on those from gravity [...] Read more.
The World-Class University/Hanyang Project launched in Korea in 2008 led to what is now called the “pseudo-conformal model” that addresses dense compact star matter and is confronted in this short note with the presently available astrophysical observables, with focus on those from gravity waves. The predictions made nearly free of parameters by the model involving “topology change” remain more or less intact “un-torpedoed” by the data. Full article
(This article belongs to the Special Issue The Nuclear Physics of Neutron Stars)
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6 pages, 324 KiB  
Article
Universal Nuclear Equation of State Introducing the Hypothetical X17 Boson
by Martin Veselský, Vlasios Petousis, Jozef Leja and Laura Navarro
Symmetry 2023, 15(1), 49; https://doi.org/10.3390/sym15010049 - 24 Dec 2022
Cited by 4 | Viewed by 1456
Abstract
Within the scope of the Symmetry journal special issue on: “The Nuclear Physics of Neutron Stars”, we complemented the nuclear equation of state (EoS) with a hypothetical 17 MeV boson and observed that only instances with an admixture of 30%–40% satisfy all of [...] Read more.
Within the scope of the Symmetry journal special issue on: “The Nuclear Physics of Neutron Stars”, we complemented the nuclear equation of state (EoS) with a hypothetical 17 MeV boson and observed that only instances with an admixture of 30%–40% satisfy all of the constraints. The successful EoS resulted in a radius of around 13 km for a neutron star with mass MNS≈1.4M⊙ and in a maximum mass of around MNS≈2.5M⊙. The value of the radius is in agreement with the recent measurement by NICER. The maximum mass is also in agreement with the mass of the remnant of the gravitational wave event GW190814. Thus, it appears that these EoSs satisfy all of the existing experimental constraints and can be considered as universal nuclear equations of state. Full article
(This article belongs to the Special Issue The Nuclear Physics of Neutron Stars)
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25 pages, 521 KiB  
Article
Mapping Topology of Skyrmions and Fractional Quantum Hall Droplets to Nuclear EFT for Ultra-Dense Baryonic Matter
by Mannque Rho
Symmetry 2022, 14(5), 994; https://doi.org/10.3390/sym14050994 - 12 May 2022
Cited by 5 | Viewed by 3066
Abstract
We describe the mapping at high density of topological structure of baryonic matter to a nuclear effective field theory that implements hidden symmetries emergent from strong nuclear correlations. The theory constructed is found to be consistent with no conflicts with the presently available [...] Read more.
We describe the mapping at high density of topological structure of baryonic matter to a nuclear effective field theory that implements hidden symmetries emergent from strong nuclear correlations. The theory constructed is found to be consistent with no conflicts with the presently available observations in both normal nuclear matter and compact-star matter. The hidden symmetries involved are “local flavor symmetry” of the vector mesons identified to be (Seiberg-)dual to the gluons of QCD and hidden “quantum scale symmetry” with an IR fixed point with a “genuine dilaton (GD)” characterized by non-vanishing pion and dilaton decay constants. Both the skyrmion topology for Nf≥2 baryons and the fractional quantum Hall (FQH) droplet topology for Nf=1 baryons are unified in the “homogeneous/hidden” Wess–Zumino term in the hidden local symmetry (HLS) Lagrangian. The possible indispensable role of the FQH droplets in going beyond the density regime of compact stars approaching scale-chiral restoration is explored by moving toward the limit where both the dilaton and the pion go massless. Full article
(This article belongs to the Special Issue The Nuclear Physics of Neutron Stars)
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11 pages, 341 KiB  
Article
Relativistic Magnetized Astrophysical Plasma Outflows in Black-Hole Microquasars
by Theodora Papavasileiou, Odysseas Kosmas and Ioannis Sinatkas
Symmetry 2022, 14(3), 485; https://doi.org/10.3390/sym14030485 - 27 Feb 2022
Cited by 6 | Viewed by 1737
Abstract
In this work, we deal with collimated outflows of magnetized astrophysical plasma known as astrophysical jets, which have been observed to emerge from a wide variety of astrophysical compact objects. The latter systems can be considered as either hydrodynamic (HD) or magnetohydrodynamic (MHD) [...] Read more.
In this work, we deal with collimated outflows of magnetized astrophysical plasma known as astrophysical jets, which have been observed to emerge from a wide variety of astrophysical compact objects. The latter systems can be considered as either hydrodynamic (HD) or magnetohydrodynamic (MHD) in nature, which means that they are governed by non-linear partial differential equations. In some of these systems, the velocity of the jet is very high and they require relativistic MHD (RMHD) treatment. We mainly focus on the appropriate numerical solutions of the MHD (and/or RMHD) equations as well as the transfer equation inside the jet and simulate multi-messenger emissions from specific astrophysical compact objects. We use a steady state axisymmetric model assuming relativistic magnetohydrodynamic descriptions for the jets (astrophysical plasma outflows) and perform numerical simulations for neutrino, gamma-ray and secondary particle emissions. By adopting the existence of such jets in black hole microquasars (and also in AGNs), the spherical symmetry of emissions is no longer valid, i.e., it is broken, and the system needs to be studied accordingly. One of the main goals is to estimate particle collision rates and particle energy distributions inside the jet, from black-hole microquasars. As concrete examples, we choose the Galactic Cygnus X-1 and the extragalactic LMC X-1 systems. Full article
(This article belongs to the Special Issue The Nuclear Physics of Neutron Stars)
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9 pages, 322 KiB  
Article
Uniqueness of the Inflationary Higgs Scalar for Neutron Stars and Failure of Non-Inflationary Approximations
by Vasilis K. Oikonomou
Symmetry 2022, 14(1), 32; https://doi.org/10.3390/sym14010032 - 28 Dec 2021
Cited by 12 | Viewed by 1544
Abstract
Neutron stars are perfect candidates to investigate the effects of a modified gravity theory, since the curvature effects are significant and more importantly, potentially testable. In most cases studied in the literature in the context of massive scalar-tensor theories, inflationary models were examined. [...] Read more.
Neutron stars are perfect candidates to investigate the effects of a modified gravity theory, since the curvature effects are significant and more importantly, potentially testable. In most cases studied in the literature in the context of massive scalar-tensor theories, inflationary models were examined. The most important of scalar-tensor models is the Higgs model, which, depending on the values of the scalar field, can be approximated by different scalar potentials, one of which is the inflationary. Since it is not certain how large the values of the scalar field will be at the near vicinity and inside a neutron star, in this work we will answer the question, which potential form of the Higgs model is more appropriate in order for it to describe consistently a static neutron star. As we will show numerically, the non-inflationary Higgs potential, which is valid for certain values of the scalar field in the Jordan frame, leads to extremely large maximum neutron star masses; however, the model is not self-consistent, because the scalar field approximation used for the derivation of the potential, is violated both at the center and at the surface of the star. These results shows the uniqueness of the inflationary Higgs potential, since it is the only approximation for the Higgs model, that provides self-consistent results. Full article
(This article belongs to the Special Issue The Nuclear Physics of Neutron Stars)
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31 pages, 1152 KiB  
Article
Unified Equation of State for Neutron Stars Based on the Gogny Interaction
by Xavier Viñas, Claudia Gonzalez-Boquera, Mario Centelles, Chiranjib Mondal and Luis M. Robledo
Symmetry 2021, 13(9), 1613; https://doi.org/10.3390/sym13091613 - 2 Sep 2021
Cited by 15 | Viewed by 2669
Abstract
The effective Gogny interactions of the D1 family were established by D. Gogny more than forty years ago with the aim to describe simultaneously the mean field and the pairing field corresponding to the nuclear interaction. The most popular Gogny parametrizations, namely D1S, [...] Read more.
The effective Gogny interactions of the D1 family were established by D. Gogny more than forty years ago with the aim to describe simultaneously the mean field and the pairing field corresponding to the nuclear interaction. The most popular Gogny parametrizations, namely D1S, D1N and D1M, describe accurately the ground-state properties of spherical and deformed finite nuclei all across the mass table obtained with Hartree–Fock–Bogoliubov (HFB) calculations. However, these forces produce a rather soft equation of state (EoS) in neutron matter, which leads to predict maximum masses of neutron stars well below the observed value of two solar masses. To remove this limitation, we built new Gogny parametrizations by modifying the density dependence of the symmetry energy predicted by the force in such a way that they can be applied to the neutron star domain and can also reproduce the properties of finite nuclei as good as their predecessors. These new parametrizations allow us to obtain stiffer EoS’s based on the Gogny interactions, which predict maximum masses of neutron stars around two solar masses. Moreover, other global properties of the star, such as the moment of inertia and the tidal deformability, are in harmony with those obtained with other well tested EoSs based on the SLy4 Skyrme force or the Barcelona–Catania–Paris–Madrid (BCPM) energy density functional. Properties of the core-crust transition predicted by these Gogny EoSs are also analyzed. Using these new Gogny forces, the EoS in the inner crust is obtained with the Wigner–Seitz approximation in the Variational Wigner–Kirkwood approach along with the Strutinsky integral method, which allows one to estimate in a perturbative way the proton shell and pairing corrections. For the outer crust, the EoS is determined basically by the nuclear masses, which are taken from the experiments, wherever they are available, or by HFB calculations performed with these new forces if the experimental masses are not known. Full article
(This article belongs to the Special Issue The Nuclear Physics of Neutron Stars)
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16 pages, 587 KiB  
Article
A Modern View of the Equation of State in Nuclear and Neutron Star Matter
by G. Fiorella Burgio, Hans-Josef Schulze, Isaac Vidaña and Jin-Biao Wei
Symmetry 2021, 13(3), 400; https://doi.org/10.3390/sym13030400 - 28 Feb 2021
Cited by 16 | Viewed by 3803
Abstract
Background: We analyze several constraints on the nuclear equation of state (EOS) currently available from neutron star (NS) observations and laboratory experiments and study the existence of possible correlations among properties of nuclear matter at saturation density with NS observables. Methods: We use [...] Read more.
Background: We analyze several constraints on the nuclear equation of state (EOS) currently available from neutron star (NS) observations and laboratory experiments and study the existence of possible correlations among properties of nuclear matter at saturation density with NS observables. Methods: We use a set of different models that include several phenomenological EOSs based on Skyrme and relativistic mean field models as well as microscopic calculations based on different many-body approaches, i.e., the (Dirac–)Brueckner–Hartree–Fock theories, Quantum Monte Carlo techniques, and the variational method. Results: We find that almost all the models considered are compatible with the laboratory constraints of the nuclear matter properties as well as with the largest NS mass observed up to now, 2.14−0.09+0.10M⊙ for the object PSR J0740+6620, and with the upper limit of the maximum mass of about 2.3–2.5M⊙ deduced from the analysis of the GW170817 NS merger event. Conclusion: Our study shows that whereas no correlation exists between the tidal deformability and the value of the nuclear symmetry energy at saturation for any value of the NS mass, very weak correlations seem to exist with the derivative of the nuclear symmetry energy and with the nuclear incompressibility. Full article
(This article belongs to the Special Issue The Nuclear Physics of Neutron Stars)
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22 pages, 2529 KiB  
Article
Probing the Nuclear Equation of State from the Existence of a ∼2.6 M⊙ Neutron Star: The GW190814 Puzzle
by Alkiviadis Kanakis-Pegios, Polychronis S. Koliogiannis and Charalampos C. Moustakidis
Symmetry 2021, 13(2), 183; https://doi.org/10.3390/sym13020183 - 24 Jan 2021
Cited by 40 | Viewed by 3626
Abstract
On 14 August 2019, the LIGO/Virgo collaboration observed a compact object with mass ∼2.59−0.09+0.08M⊙, as a component of a system where the main companion was a black hole with mass ∼23M⊙. [...] Read more.
On 14 August 2019, the LIGO/Virgo collaboration observed a compact object with mass ∼2.59−0.09+0.08M⊙, as a component of a system where the main companion was a black hole with mass ∼23M⊙. A scientific debate initiated concerning the identification of the low mass component, as it falls into the neutron star–black hole mass gap. The understanding of the nature of GW190814 event will offer rich information concerning open issues, the speed of sound and the possible phase transition into other degrees of freedom. In the present work, we made an effort to probe the nuclear equation of state along with the GW190814 event. Firstly, we examine possible constraints on the nuclear equation of state inferred from the consideration that the low mass companion is a slow or rapidly rotating neutron star. In this case, the role of the upper bounds on the speed of sound is revealed, in connection with the dense nuclear matter properties. Secondly, we systematically study the tidal deformability of a possible high mass candidate existing as an individual star or as a component one in a binary neutron star system. As the tidal deformability and radius are quantities very sensitive on the neutron star equation of state, they are excellent counters on dense matter properties. We conjecture that similar isolated neutron stars or systems may exist in the universe and their possible future observation will shed light on the maximum neutron star mass problem. Full article
(This article belongs to the Special Issue The Nuclear Physics of Neutron Stars)
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