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Properties and Dynamics of Neutron Stars and Proto-Neutron Stars

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A special issue of Universe (ISSN 2218-1997). This special issue belongs to the section "Compact Objects".

Deadline for manuscript submissions: closed (31 March 2022) | Viewed by 28351

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Special Issue Editors

Prof. Dr. Veronica Dexheimer

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Guest Editor

Department of Physics, Kent State University, Kent, OH 44242, USA
Interests: neutron stars; dense matter; QCD phase diagrams; magnetic fields

Prof. Dr. Rodrigo Negreiros

E-Mail Website
Guest Editor

Instituto de Física, Universidade Federal Fluminense, Praia Vermelha 24210-346, Brazil
Interests: neutron stars; stellar cooling; general relativity; dense matter
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Special Issue Information

Based on your expertise, we would like to invite you to submit a contribution to the upcoming Special Issue of Universe entitled “Properties and Dynamics of Neutron Stars and Proto-Neutron Stars”.

Following new developments in measurements of gravitational waves from neutron-star mergers and modification or construction of particle colliders to reach larger densities, we are entering a new era, in which we can for the first time begin to understand dense and hot matter. This, together with future supernova explosion data, will provide us for the first time with the opportunity to have truly multimessenger data on hot and dense matter, which is to some extent similar to the matter present in the core of proto-neutron stars.

This Special Issue focuses on the theory necessary to understand the present data and data to come in the future. It includes state-of-the-art theorical models that describe dense and hot matter and dynamical stellar simulations that make use of them, with the ultimate goal of determining which degrees of freedom are relevant under these conditions and how they affect the matter equation of state and stellar evolution.

Prof. Dr. Veronica Dexheimer
Prof. Dr. Rodrigo Negreiros
Guest Editors

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. Universe is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. 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

dense and hot matter
proto-neutron star
supernova explosion
compact star cooling
neutron-star mergers

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Published Papers (12 papers)

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Editorial

Jump to: Research, Review, Other

4 pages, 236 KiB

Open AccessEditorial

Properties and Dynamics of Neutron Stars and Proto-Neutron Stars

by Veronica Dexheimer

Universe 2022, 8(8), 434; https://doi.org/10.3390/universe8080434 - 21 Aug 2022

Cited by 1 | Viewed by 1429

Abstract

This Special Issue provides a comprehensive collection of papers that present modern theories to describe neutron star interiors and dynamics [...] Full article

(This article belongs to the Special Issue Properties and Dynamics of Neutron Stars and Proto-Neutron Stars)

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Research

Jump to: Editorial, Review, Other

18 pages, 3401 KiB

Open AccessArticle

Low Density Neutron Star Matter with Quantum Molecular Dynamics: The Role of Isovector Interactions

by Parit Mehta, Rana Nandi, Rosana de Oliveira Gomes, Veronica Dexheimer and Jan Steinheimer

Universe 2022, 8(7), 380; https://doi.org/10.3390/universe8070380 - 13 Jul 2022

Cited by 2 | Viewed by 1641

Abstract

The effect of isospin-dependent nuclear forces on the inner crust of neutron stars is modeled within the framework of Quantum Molecular Dynamics (QMD). To successfully control the density dependence of the symmetry energy of neutron-star matter below nuclear saturation density, a mixed vector-isovector potential is introduced. This approach is inspired by the baryon density and isospin density-dependent repulsive Skyrme force of asymmetric nuclear matter. In isospin-asymmetric nuclear matter, the system shows nucleation, as nucleons are arranged into shapes resembling nuclear pasta. The dependence of clusterization in the system on the isospin properties is also explored by calculating two-point correlation functions. We show that, as compared to previous results that did not involve such mixed interaction terms, the energy symmetry slope L is successfully controlled by varying the corresponding coupling strength. Nevertheless, the effect of changing the slope of the nuclear symmetry energy L on the crust-core transition density does not seem significant. To the knowledge of the authors, this is the first implementation of such a coupling in a QMD model for isospin asymmetric matter, which is relevant to the inner crust of neutron and proto-neutron stars. Full article

(This article belongs to the Special Issue Properties and Dynamics of Neutron Stars and Proto-Neutron Stars)

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24 pages, 482 KiB

Open AccessArticle

The Macro-Physics of the Quark-Nova: Astrophysical Implications

by Rachid Ouyed

Universe 2022, 8(6), 322; https://doi.org/10.3390/universe8060322 - 9 Jun 2022

Cited by 4 | Viewed by 2060

Abstract

A quark-nova is a hypothetical stellar evolution branch where a neutron star converts explosively into a quark star. Here, we discuss the intimate coupling between the micro-physics and macro-physics of the quark-nova and provide a prescription for how to couple the Burn-UD code to the stellar evolution code in order to simulate neutron-star-to-quark-star burning at stellar scales and estimate the resulting energy release and ejecta. Once formed, the thermal evolution of the proto-quark star follows. We found much higher peak neutrino luminosities (>10

^{55}

erg/s) and a higher energy neutrino (i.e., harder) spectrum than previous stellar evolution studies of proto-neutron stars. We derived the neutrino counts that observatories such as Super-Kamiokande-III and Halo-II should expect and suggest how these can differentiate between a supernova and a quark-nova. Due to the high peak neutrino luminosities, neutrino pair annihilation can deposit as much as

10^{52}

ergs in kinetic energy in the matter overlaying the neutrinosphere, yielding relativistic quark-nova ejecta. We show how the quark-nova could help us understand many still enigmatic high-energy astrophysical transients, such as super-luminous supernovae, gamma-ray bursts and fast radio bursts. Full article

(This article belongs to the Special Issue Properties and Dynamics of Neutron Stars and Proto-Neutron Stars)

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24 pages, 2360 KiB

Open AccessArticle

Radial Oscillations of Quark Stars Admixed with Dark Matter

by José C. Jiménez and Eduardo S. Fraga

Universe 2022, 8(1), 34; https://doi.org/10.3390/universe8010034 - 5 Jan 2022

Cited by 24 | Viewed by 1791

Abstract

We investigated compact stars consisting of cold quark matter and fermionic dark matter treated as two admixed fluids. We computed the stellar structures and fundamental radial oscillation frequencies of different masses of the dark fermion in the cases of weak and strong self-interacting dark matter. We found that the fundamental frequency can be dramatically modified and, in some cases, stable dark strange planets and dark strangelets with very low masses and radii can be formed. Full article

(This article belongs to the Special Issue Properties and Dynamics of Neutron Stars and Proto-Neutron Stars)

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28 pages, 4455 KiB

Open AccessArticle

Beta Equilibrium under Neutron Star Merger Conditions

by Mark G. Alford, Alexander Haber, Steven P. Harris and Ziyuan Zhang

Universe 2021, 7(11), 399; https://doi.org/10.3390/universe7110399 - 22 Oct 2021

Cited by 37 | Viewed by 2810

Abstract

We calculate the nonzero-temperature correction to the beta equilibrium condition in nuclear matter under neutron star merger conditions, in the temperature range 1mEv < T ≲ 5 mEv. We improve on previous work using a consistent description of nuclear matter based on the IUF and SFHo relativistic mean field models. This includes using relativistic dispersion relations for the nucleons, which we show is essential in these models. We find that the nonzero-temperature correction can be of order 10 to 20 MeV, and plays an important role in the correct calculation of Urca rates, which can be wrong by factors of 10 or more if it is neglected. Full article

(This article belongs to the Special Issue Properties and Dynamics of Neutron Stars and Proto-Neutron Stars)

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16 pages, 682 KiB

Open AccessArticle

Equation of State and Composition of Proto-Neutron Stars and Merger Remnants with Hyperons

by Armen Sedrakian and Arus Harutyunyan

Universe 2021, 7(10), 382; https://doi.org/10.3390/universe7100382 - 15 Oct 2021

Cited by 13 | Viewed by 1774

Abstract

Finite-temperature equation of state (EoS) and the composition of dense nuclear and hypernuclear matter under conditions characteristic of neutron star binary merger remnants and supernovas are discussed. We consider both neutrino free-streaming and trapped regimes which are separated by a temperature of a few MeV. The formalism is based on covariant density functional (CDF) theory for the full baryon octet with density-dependent couplings, suitably adjusted in the hypernuclear sector. The softening of the EoS with the introduction of the hyperons is quantified under various conditions of lepton fractions and temperatures. We find that

Λ

Ξ^{-}

, and

Ξ^{0}

hyperons appear in the given order with a sharp density increase at zero temperature at the threshold being replaced by an extended increment over a wide density range at high temperatures. The

Λ

hyperon survives in the deep subnuclear regime. The triplet of

Σ

s is suppressed in cold hypernuclear matter up to around seven times the nuclear saturation density, but appears in significant fractions at higher temperatures,

T \geq 20

MeV, in both supernova and merger remnant matter. We point out that a special isospin degeneracy point exists where the baryon abundances within each of the three isospin multiplets are equal to each other as a result of (approximate) isospin symmetry. At that point, the charge chemical potential of the system vanishes. We find that under the merger remnant conditions, the fractions of electron and

μ

-on neutrinos are close and are about 1%, whereas in the supernova case, we only find a significant fraction (∼10%) of electron neutrinos, given that in this case, the

μ

-on lepton number is zero. Full article

(This article belongs to the Special Issue Properties and Dynamics of Neutron Stars and Proto-Neutron Stars)

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22 pages, 1062 KiB

Open AccessArticle

The Nuclear Matter Density Functional under the Nucleonic Hypothesis

by Hoa Dinh Thi, Chiranjib Mondal and Francesca Gulminelli

Universe 2021, 7(10), 373; https://doi.org/10.3390/universe7100373 - 6 Oct 2021

Cited by 30 | Viewed by 2445

Abstract

A Bayesian analysis of the possible behaviors of the dense matter equation of state informed by recent LIGO-Virgo as well as NICER measurements reveals that all the present observations are compatible with a fully nucleonic hypothesis for the composition of dense matter, even in the core of the most massive pulsar PSR J0740+6620. Under the hypothesis of a nucleonic composition, we extract the most general behavior of the energy per particle of symmetric matter and density dependence of the symmetry energy, compatible with the astrophysical observations as well as our present knowledge of low-energy nuclear physics from effective field theory predictions and experimental nuclear mass data. These results can be used as a null hypothesis to be confronted with future constraints on dense matter to search for possible exotic degrees of freedom. Full article

(This article belongs to the Special Issue Properties and Dynamics of Neutron Stars and Proto-Neutron Stars)

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19 pages, 1042 KiB

Open AccessArticle

Hybrid Stars with Color Superconducting Cores in an Extended FCM Model

by Daniela Curin, Ignacio Francisco Ranea-Sandoval, Mauro Mariani, Milva Gabriela Orsaria and Fridolin Weber

Universe 2021, 7(10), 370; https://doi.org/10.3390/universe7100370 - 1 Oct 2021

Cited by 11 | Viewed by 1907

Abstract

We investigate the influence of repulsive vector interactions and color superconductivity on the structure of neutron stars using an extended version of the field correlator method (FCM) for the description of quark matter. The hybrid equation of state is constructed using the Maxwell description, which assumes a sharp hadron-quark phase transition. The equation of state of hadronic matter is computed for a density-dependent relativistic lagrangian treated in the mean-field approximation, with parameters given by the SW4L nuclear model. This model described the interactions among baryons in terms of

σ, ω, ρ, σ^{*}

, and

ϕ

mesons. Quark matter is assumed to be in either the CFL or the 2SC+s color superconducting phase. The possibility of sequential (hadron-quark, quark-quark) transitions in ultra-dense matter is investigated. Observed data related to massive pulsars, gravitational-wave events, and NICER are used to constrain the parameters of the extended FCM model. The successful equations of state are used to explore the mass-radius relationship, radii, and tidal deformabilities of hybrid stars. A special focus lies on investigating consequences that slow or fast conversions of quark-hadron matter have on the stability and the mass-radius relationship of hybrid stars. We find that if slow conversion should occur, a new branch of stable massive stars would exist whose members have radii that are up to 1.5 km smaller than those of conventional neutron stars of the same mass. Such objects could be possible candidates for the stellar high-mass object of the GW190425 binary system. Full article

(This article belongs to the Special Issue Properties and Dynamics of Neutron Stars and Proto-Neutron Stars)

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14 pages, 4006 KiB

Open AccessEditor’s ChoiceArticle

High-Order Multipole and Binary Love Number Universal Relations

by Daniel A. Godzieba and David Radice

Universe 2021, 7(10), 368; https://doi.org/10.3390/universe7100368 - 30 Sep 2021

Cited by 11 | Viewed by 2085 | Correction

Abstract

Using a data set of approximately 2 million phenomenological equations of state consistent with observational constraints, we construct new equation-of-state-insensitive universal relations that exist between the multipolar tidal deformability parameters of neutron stars,

Λ_{l}

, for several high-order multipoles ( [...] Read more.

Λ_{l}

, for several high-order multipoles (

l = 5, 6, 7, 8

), and we consider finite-size effects of these high-order multipoles in waveform modeling. We also confirm the existence of a universal relation between the radius of the

1.4 M_{⊙}

NS,

R_{1.4}

and the reduced tidal parameter of the binary,

\tilde{Λ}

, and the chirp mass. We extend this relation to a large number of chirp masses and to the radii of isolated NSs of different mass M,

R_{M}

. We find that there is an optimal value of M for every

M

such that the uncertainty in the estimate of

R_{M}

is minimized when using the relation. We discuss the utility and implications of these relations for the upcoming LIGO O4 run and third-generation detectors. Full article

(This article belongs to the Special Issue Properties and Dynamics of Neutron Stars and Proto-Neutron Stars)

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41 pages, 2827 KiB

Open AccessEditor’s ChoiceArticle

A Neutron Star Is Born

by Débora Peres Menezes

Universe 2021, 7(8), 267; https://doi.org/10.3390/universe7080267 - 26 Jul 2021

Cited by 26 | Viewed by 5739

Abstract

A neutron star was first detected as a pulsar in 1967. It is one of the most mysterious compact objects in the universe, with a radius of the order of 10 km and masses that can reach two solar masses. In fact, neutron stars are star remnants, a kind of stellar zombie (they die, but do not disappear). In the last decades, astronomical observations yielded various contraints for neutron star masses, and finally, in 2017, a gravitational wave was detected (GW170817). Its source was identified as the merger of two neutron stars coming from NGC 4993, a galaxy 140 million light years away from us. The very same event was detected in

γ

-ray, X-ray, UV, IR, radio frequency and even in the optical region of the electromagnetic spectrum, starting the new era of multi-messenger astronomy. To understand and describe neutron stars, an appropriate equation of state that satisfies bulk nuclear matter properties is necessary. GW170817 detection contributed with extra constraints to determine it. On the other hand, magnetars are the same sort of compact object, but bearing much stronger magnetic fields that can reach up to 10

^{15}

G on the surface as compared with the usual 10

^{12}

G present in ordinary pulsars. While the description of ordinary pulsars is not completely established, describing magnetars poses extra challenges. In this paper, I give an overview on the history of neutron stars and on the development of nuclear models and show how the description of the tiny world of the nuclear physics can help the understanding of the cosmos, especially of the neutron stars. Full article

(This article belongs to the Special Issue Properties and Dynamics of Neutron Stars and Proto-Neutron Stars)

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Review

Jump to: Editorial, Research, Other

26 pages, 1171 KiB

Open AccessReview

Magnetic Dual Chiral Density Wave: A Candidate Quark Matter Phase for the Interior of Neutron Stars

by Efrain J. Ferrer and Vivian de la Incera

Universe 2021, 7(12), 458; https://doi.org/10.3390/universe7120458 - 23 Nov 2021

Cited by 12 | Viewed by 1839

Abstract

In this review, we discuss the physical characteristics of the magnetic dual chiral density wave (MDCDW) phase of dense quark matter and argue why it is a promising candidate for the interior matter phase of neutron stars. The MDCDW condensate occurs in the presence of a magnetic field. It is a single-modulated chiral density wave characterized by two dynamically generated parameters: the fermion quasiparticle mass m and the condensate spatial modulation q. The lowest-Landau-level quasiparticle modes in the MDCDW system are asymmetric about the zero energy, a fact that leads to the topological properties and anomalous electric transport exhibited by this phase. The topology makes the MDCDW phase robust against thermal phonon fluctuations, and as such, it does not display the Landau–Peierls instability, a staple feature of single-modulated inhomogeneous chiral condensates in three dimensions. The topology is also reflected in the presence of the electromagnetic chiral anomaly in the effective action and in the formation of hybridized propagating modes known as axion-polaritons. Taking into account that one of the axion-polaritons of this quark phase is gapped, we argue how incident

γ

-ray photons can be converted into gapped axion-polaritons in the interior of a magnetar star in the MDCDW phase leading the star to collapse, a phenomenon that can serve to explain the so-called missing pulsar problem in the galactic center. Full article

(This article belongs to the Special Issue Properties and Dynamics of Neutron Stars and Proto-Neutron Stars)

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