Submit to Galaxies Review for Galaxies Propose a Special Issue

Journal Menu

Journal Browser

► Journal Browser

Neutron Stars and Hadrons in the Era of Gravitational Wave Astrophysics

Print Special Issue Flyer
Special Issue Editors
Special Issue Information
Keywords
Published Papers

A special issue of Galaxies (ISSN 2075-4434).

Deadline for manuscript submissions: closed (20 April 2022) | Viewed by 12323

Share This Special Issue

Special Issue Editor

Dr. Plamen G. Krastev

E-Mail Website
Guest Editor

Research Computing, Faculty of Arts and Sciences, Harvard University, Cambridge, MA 02138, USA
Interests: theoretical nuclear physics and astrophysics; neutron stars; gravitational waves; effective interactions in neutron-rich matter; equation of state of dense nuclear matter; numerical relativity; high performance computing; artificial intelligence

Special Issue Information

Dear Colleagues,

The direct detection of gravitational waves (GWs) confirmed the last remaining prediction of General Relativity and initiated a new era of gravitational wave astrophysics, which enables observations of violent cosmic events that were not previously possible and will potentially allow looking directly into the very early history of the universe. During the first (O1) and second (O2) observing runs, the LIGO and VIRGO collaborations reported eleven GW signals from compact binary mergers, which included the first signal from a binary neutron star (BNS) coalescence, GW170817. The observation of GW170817 in both gravitational and electromagnetic (EM) spectra inaugurated the field of multi-messenger astrophysics (MMA), which uses GWs, EM radiation, cosmic rays, and neutrinos to provide complimentary information about the astrophysical processes and environments of MMA sources. This event simultaneously confirmed the nature of the short gamma-ray bursts (GRBs), kilonovae, the origin of the heavy elements, and placed stringent constraints on the velocity difference of EM and gravitational waves. Furthermore, the third observing LIGO run (O3) has identified tens of candidate GW events, among which several signals involving neutron stars—both BNS and black-hole neutron-star (BHNS) merger events. With the improvement of GW detector sensitivity and with new observatories joining the detector network, many more observations, including BNS and BHNS events, are likely to be detected on a regular basis.

Neutron stars are extraordinary cosmic nuclear and particle physics laboratories providing unique testing grounds for studying strong interactions and dense matter in regimes which are impossible to explore in the terrestrial laboratories. These fascinating astrophysical objects have been studied actively for decades, and the latest developments reignite the interest in nuclear and particle physics and put these fields at the forefront of research endeavors. Indeed, the study of neutron stars is a truly interdisciplinary effort where general relativity uses input from nuclear and particle physics, and conversely, neutron star observations provide key constraints to nuclear and particle physics. For instance, the equation of state (EOS) of dense, neutron-rich matter is the most important ingredient for solving the neutron star structure equations to obtain the renowned mass-radius diagram and related observables and also governs the dynamics of the BNS mergers and the emission of GWs. Additionally, QCD guides our understanding of whether any novel phases of matter can be realized in neutron star interiors. On the other hand, GW observations of neutron stars provide constraints on neutron-star tidal deformability, and in turn, on the underlying EOS and fundamental interparticle interactions.

The main purpose of this Special Issue is therefore to reassess the current standing of the field, what progress is presently being made in our understanding of neutron stars and dense matter in the light of gravitational astrophysics, and what developments we should anticipate in the near future. As a guest editor for this Special Issue, I am glad to assist the Galaxies editorial board in the task of compiling the best and most current research on neutron stars as an intersection of nuclear and particle physics and general relativity. We look forward to your submission.

Dr. Plamen G. Krastev
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 papers will be 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. Galaxies is an international peer-reviewed open access quarterly 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

neutron stars
gravitational waves
dense matter
equation of state
tidal deformability

Published Papers (5 papers)

Download All Papers

Research

Jump to: Review

20 pages, 1785 KiB

Open AccessArticle

Neutron Star Radii, Deformabilities, and Moments of Inertia from Experimental and Ab Initio Theory Constraints of the ²⁰⁸Pb Neutron Skin Thickness

by Yeunhwan Lim and Jeremy W. Holt

Galaxies 2022, 10(5), 99; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies10050099 - 20 Sep 2022

Cited by 12 | Viewed by 1627

Abstract

Recent experimental and ab initio theory investigations of the

^{208}

Pb neutron skin thickness have the potential to inform the neutron star equation of state. In particular, the strong correlation between the

^{208}

Pb neutron skin thickness and the pressure of neutron matter [...] Read more.

Recent experimental and ab initio theory investigations of the

^{208}

Pb neutron skin thickness have the potential to inform the neutron star equation of state. In particular, the strong correlation between the

^{208}

Pb neutron skin thickness and the pressure of neutron matter at normal nuclear densities leads to modified predictions for the radii, tidal deformabilities, and moments of inertia of typical

1.4 M_{⊙}

neutron stars. In the present work, we study the relative impact of these recent analyses of the

^{208}

Pb neutron skin thickness on bulk properties of neutron stars within a Bayesian statistical analysis. Two models for the equation of state prior are employed in order to highlight the role of the highly uncertain high-density equation of state. From our combined Bayesian analysis of nuclear theory, nuclear experiment, and observational constraints on the dense matter equation of state, we find at the 90% credibility level

R_{1.4} = 12 . 36_{- 0.73}^{+ 0.38}

km for the radius of a

1.4 M_{⊙}

neutron star,

R_{2.0} = 11 . 96_{- 0.71}^{+ 0.94}

km for the radius of a

2.0 M_{⊙}

neutron star,

Λ_{1.4} = 440_{- 144}^{+ 103}

for the tidal deformability of a

1.4 M_{⊙}

neutron star, and

I_{1.338} = 1 . 425_{- 0.146}^{+ 0.074} \times 10^{45} {g cm}^{2}

for the moment of inertia of PSR J0737-3039A whose mass is

1.338 M_{⊙}

. Full article

(This article belongs to the Special Issue Neutron Stars and Hadrons in the Era of Gravitational Wave Astrophysics)

► Show Figures

Figure 1

11 pages, 1128 KiB

Open AccessArticle

Temperature Effects on Core g-Modes of Neutron Stars

by Nicholas Lozano, Vinh Tran and Prashanth Jaikumar

Galaxies 2022, 10(4), 79; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies10040079 - 28 Jun 2022

Cited by 4 | Viewed by 1569

Abstract

Neutron stars provide a unique physical laboratory in which to study the properties of matter at high density and temperature. We study a diagnostic of the composition of high-density matter, namely, g-mode oscillations, which are driven by buoyancy forces. These oscillations can be excited by tidal forces and couple to gravitational waves. We extend prior results for the g-mode spectrum of cold neutron star matter to high temperatures that are expected to be achieved in neutron star mergers using a parameterization for finite-temperature effects on equations of state recently proposed by Raithel, Özel and Psaltis. We find that the g-modes of canonical mass neutron stars (≈1.4

M_{⊙}

) are suppressed at high temperatures, and core g-modes are supported only in the most massive (≥2

M_{⊙}

) of hot neutron stars. Full article

(This article belongs to the Special Issue Neutron Stars and Hadrons in the Era of Gravitational Wave Astrophysics)

► Show Figures

Figure 1

19 pages, 4605 KiB

Open AccessArticle

Translating Neutron Star Observations to Nuclear Symmetry Energy via Deep Neural Networks

by Plamen G. Krastev

Galaxies 2022, 10(1), 16; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies10010016 - 18 Jan 2022

Cited by 22 | Viewed by 3098

Abstract

One of the most significant challenges involved in efforts to understand the equation of state of dense neutron-rich matter is the uncertain density dependence of the nuclear symmetry energy. In particular, the nuclear symmetry energy is still rather poorly constrained, especially at high densities. On the other hand, detailed knowledge of the equation of state is critical for our understanding of many important phenomena in the nuclear terrestrial laboratories and the cosmos. Because of its broad impact, pinning down the density dependence of the nuclear symmetry energy has been a long-standing goal of both nuclear physics and astrophysics. Recent observations of neutron stars, in both electromagnetic and gravitational-wave spectra, have already constrained significantly the nuclear symmetry energy at high densities. The next generation of telescopes and gravitational-wave observatories will provide an unprecedented wealth of detailed observations of neutron stars, which will improve further our knowledge of the density dependence of nuclear symmetry energy, and the underlying equation of state of dense neutron-rich matter. Training deep neural networks to learn a computationally efficient representation of the mapping between astrophysical observables of neutron stars, such as masses, radii, and tidal deformabilities, and the nuclear symmetry energy allows its density dependence to be determined reliably and accurately. In this work, we use a deep learning approach to determine the nuclear symmetry energy as a function of density directly from observational neutron star data. We show, for the first time, that artificial neural networks can precisely reconstruct the nuclear symmetry energy from a set of available neutron star observables, such as masses and radii as measured by, e.g., the NICER mission, or masses and tidal deformabilities as measured by the LIGO/VIRGO/KAGRA gravitational-wave detectors. These results demonstrate the potential of artificial neural networks to reconstruct the symmetry energy and the equation of state directly from neutron star observational data, and emphasize the importance of the deep learning approach in the era of multi-messenger astrophysics. Full article

(This article belongs to the Special Issue Neutron Stars and Hadrons in the Era of Gravitational Wave Astrophysics)

► Show Figures

Figure 1

16 pages, 6506 KiB

Open AccessFeature PaperArticle

Detectability of Continuous Gravitational Waves from Magnetically Deformed Neutron Stars

by Jacopo Soldateschi and Niccolò Bucciantini

Galaxies 2021, 9(4), 101; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9040101 - 10 Nov 2021

Cited by 6 | Viewed by 2157

Abstract

Neutron stars are known to contain extremely powerful magnetic fields. Their effect is to deform the shape of the star, leading to the potential emission of continuous gravitational waves. The magnetic deformation of neutron stars, however, depends on the geometry and strength of their internal magnetic field as well as on their composition, described by the equation of state. Unfortunately, both the configuration of the magnetic field and the equation of state of neutron stars are unknown, and assessing the detectability of continuous gravitational waves from neutron stars suffers from these uncertainties. Using our recent results relating the magnetic deformation of a neutron star to its mass and radius—based on models with realistic equations of state currently allowed by observational and nuclear physics constraints—and considering the Galactic pulsar population, we assess the detectability of continuous gravitational waves from pulsars in the galaxy by current and future gravitational waves detectors. Full article

(This article belongs to the Special Issue Neutron Stars and Hadrons in the Era of Gravitational Wave Astrophysics)

► Show Figures

Figure 1

Review

Jump to: Research

17 pages, 1596 KiB

Open AccessReview

Dark Matter Effects on the Compact Star Properties

by H. C. Das, Ankit Kumar, Bharat Kumar and Suresh Kumar Patra

Galaxies 2022, 10(1), 14; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies10010014 - 18 Jan 2022

Cited by 17 | Viewed by 2656

Abstract

The neutron star properties are generally determined by the equation of state of

β

The neutron star properties are generally determined by the equation of state of

β

-equilibrated dense matter. In this work, we consider the interaction of fermionic dark matter (DM) particles with nucleons via Higgs exchange and investigate the effect on the neutron star properties with the relativistic mean-field model equation of state coupled with DM. We deduce that DM significantly affects the neutron star properties, such as considerably reducing the maximum mass of the star, which depends on the percentage of the DM considered inside the neutron star. The tidal Love numbers both for electric and magnetic cases and surficial Love numbers are also studied for DM admixed NS. We observed that the magnitude of tidal and surficial Love numbers increases with a greater DM percentage. Further, we present post-Newtonian tidal corrections to gravitational waves decreased by increasing the DM percentage. The DM effect on the GW signal is significant during the late inspiral and merger stages of binary evolution for GW frequencies >500 Hz. Full article

(This article belongs to the Special Issue Neutron Stars and Hadrons in the Era of Gravitational Wave Astrophysics)

► Show Figures