Special Issue "The Nuclear Physics of Neutron Stars"

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

Deadline for manuscript submissions: 20 November 2022 | Viewed by 3757

Special Issue Editor

Dr. Charalampos Moustakidis
E-Mail Website
Guest Editor
Department of Nuclear and Elementaty Particle Physics, School of Physics Faculty of Sciences, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
Interests: nuclear astrophysics; nuclear structure; quantum information

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.

Dr. Charalampos Moustakidis
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

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

Published Papers (5 papers)

Order results
Result details
Select all
Export citation of selected articles as:

Research

Article
Relativistic Magnetized Astrophysical Plasma Outflows in Black-Hole Microquasars
Symmetry 2022, 14(3), 485; https://doi.org/10.3390/sym14030485 - 27 Feb 2022
Viewed by 514
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)
Show Figures

Figure 1

Article
Uniqueness of the Inflationary Higgs Scalar for Neutron Stars and Failure of Non-Inflationary Approximations
Symmetry 2022, 14(1), 32; https://doi.org/10.3390/sym14010032 - 28 Dec 2021
Viewed by 385
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)
Show Figures

Figure 1

Article
Unified Equation of State for Neutron Stars Based on the Gogny Interaction
Symmetry 2021, 13(9), 1613; https://doi.org/10.3390/sym13091613 - 02 Sep 2021
Cited by 5 | Viewed by 532
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)
Show Figures

Figure 1

Article
A Modern View of the Equation of State in Nuclear and Neutron Star Matter
Symmetry 2021, 13(3), 400; https://doi.org/10.3390/sym13030400 - 28 Feb 2021
Cited by 7 | Viewed by 808
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, 2.140.09+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)
Show Figures

Figure 1

Article
Probing the Nuclear Equation of State from the Existence of a ∼2.6 M Neutron Star: The GW190814 Puzzle
Symmetry 2021, 13(2), 183; https://doi.org/10.3390/sym13020183 - 24 Jan 2021
Cited by 24 | Viewed by 808
Abstract
On 14 August 2019, the LIGO/Virgo collaboration observed a compact object with mass 2.590.09+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 2.590.09+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)
Show Figures

Figure 1

Back to TopTop