Special Issue "Compact Stars in the QCD Phase Diagram and in the Multi-Messenger Era of Astronomy"

A special issue of Universe (ISSN 2218-1997).

Deadline for manuscript submissions: closed (8 May 2019).

Special Issue Editors

Guest Editor
Prof. Vivian De la Incera

City University of New York/College of Staten Island, New York 10314, USA
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Interests: QCD Phases; External field effects; Transport in dense matter
Guest Editor
Prof. Efrain Ferrer

City University of New York/College of Staten Island, New York 10314, USA
Website | E-Mail
Interests: QCD under extreme conditions; Equation of state in neutron stars
Guest Editor
Prof. Jim Lattimer

State University of New York at Stony Brook, Stony Brook, NY 11794, USA
Website | E-Mail
Interests: Neutron star cooling; Supernovae explosions; Properties of hot; Dense matter; Binary mergers
Guest Editor
Prof. Dr. David Blaschke

1. Institute of Theoretical Physics, University of Wroclaw, 50-204 Wroclaw, Poland
2. Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, 141980 Dubna, Russia
3. National Research Nuclear University (MEPhI), 115409 Moscow, Russia
Website | E-Mail
Interests: quantum field theory; quantum statistics; quark gluon plasma; heavy ion collisions; compact stars

Special Issue Information

Dear Colleagues,

This Special Issue is dedicated to the conference: Compact Stars in the QCD Phase Diagram VII: https://www.csi.cuny.edu/academics-and-research/conferences/csqcd-vii

The CSQCD VII conference brought together astrophysicists and nuclear physicists to discuss how the new multi-messenger era in astrophysics can serve to constrain the equation of state of the matter inside neutron stars and help to identify viable phases for the star's interior, its transport properties, and evolution. These proceedings feature articles reflecting a special forum held at the conference on the ways nuclear physicists and astrophysicists can work together to tackle the most challenging problems in the overlapping areas of neutron stars and dense QCD, and how these efforts may serve to inform and guide preparations for future multi-messenger observations.

This Special Issue covers the following main topics:

  •  Equation of state and neutron star mergers
  •  Phases of dense quark matter
  •  External field effects on dense matter and neutron stars
  •  Transport in dense QCD and neutron stars
  •  Strangeness in compact stars
  •  Supernovae and high energy astrophysics of neutron stars and binary mergers

Prof. Vivian de la Incera
Prof. Efrain Ferrer
Prof. Jim Lattimer
Prof. David Blaschke
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 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. 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

  • Supernovae, Neutron Stars, and Neutron Star Mergers
  • QCD Phases
  • Gravitational waves
  • Transport in Dense Quark Matter
  • Strange Matter in Neutron Stars

Published Papers (10 papers)

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Research

Open AccessArticle
Impact of the Nuclear Equation of State on the Stability of Hybrid Neutron Stars
Universe 2019, 5(8), 186; https://doi.org/10.3390/universe5080186
Received: 8 May 2019 / Revised: 7 August 2019 / Accepted: 8 August 2019 / Published: 12 August 2019
PDF Full-text (330 KB)
Abstract
We construct a set of equations of state (EoS) of dense and hot matter with a 1st order phase transition from a hadronic system to a deconfined quark matter state. In this two-phase approach, hadrons are described using the relativistic mean field theory [...] Read more.
We construct a set of equations of state (EoS) of dense and hot matter with a 1st order phase transition from a hadronic system to a deconfined quark matter state. In this two-phase approach, hadrons are described using the relativistic mean field theory with different parametrisations and the deconfined quark phase is modeled using vBag, a bag–type model extended to include vector interactions as well as a simultaneous onset of chiral symmetry restoration and deconfinement. This feature results in a non–trivial connection between the hadron and quark EoS, modifying the quark phase beyond its onset density. We find that this unique property has an impact on the predicted hybrid (quark core) neutron star mass–radius relations. Full article
Open AccessArticle
Parity Doubling and the Dense-Matter Phase Diagram under Constraints from Multi-Messenger Astronomy
Universe 2019, 5(8), 180; https://doi.org/10.3390/universe5080180
Received: 14 May 2019 / Revised: 24 July 2019 / Accepted: 26 July 2019 / Published: 30 July 2019
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Abstract
We extend the recently developed hybrid quark–meson–nucleon model by augmenting a six-point scalar interaction and investigate the consequences for neutron-star sequences in the mass–radius diagram. One of the characteristic features of the model is that the chiral symmetry is restored within the hadronic [...] Read more.
We extend the recently developed hybrid quark–meson–nucleon model by augmenting a six-point scalar interaction and investigate the consequences for neutron-star sequences in the mass–radius diagram. One of the characteristic features of the model is that the chiral symmetry is restored within the hadronic phase by lifting the mass splitting between chiral partner states, before quark deconfinement takes place. At low temperature and finite baryon density, the model predicts a first- or second-order chiral phase transition, or a crossover, depending on the expectation value of a scalar field, and a first-order deconfinement phase transition. We discuss two sets of free parameters, which result in compact-star mass–radius relations that are at tension with the combined constraints for maximum-mass ( 2 M ) and the compactness (GW170817). We find that the most preferable mass–radius relations result in isospin-symmetric phase diagram with rather low temperature for the critical point of the chiral phase transition. Full article
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Open AccessArticle
Phases of Hadron-Quark Matter in (Proto) Neutron Stars
Universe 2019, 5(7), 169; https://doi.org/10.3390/universe5070169
Received: 13 May 2019 / Revised: 5 July 2019 / Accepted: 8 July 2019 / Published: 11 July 2019
Cited by 1 | PDF Full-text (1008 KB) | HTML Full-text | XML Full-text
Abstract
In the first part of this paper, we investigate the possible existence of a structured hadron-quark mixed phase in the cores of neutron stars. This phase, referred to as the hadron-quark pasta phase, consists of spherical blob, rod, and slab rare phase geometries. [...] Read more.
In the first part of this paper, we investigate the possible existence of a structured hadron-quark mixed phase in the cores of neutron stars. This phase, referred to as the hadron-quark pasta phase, consists of spherical blob, rod, and slab rare phase geometries. Particular emphasis is given to modeling the size of this phase in rotating neutron stars. We use the relativistic mean-field theory to model hadronic matter and the non-local three-flavor Nambu–Jona-Lasinio model to describe quark matter. Based on these models, the hadron-quark pasta phase exists only in very massive neutron stars, whose rotational frequencies are less than around 300 Hz. All other stars are not dense enough to trigger quark deconfinement in their cores. Part two of the paper deals with the quark-hadron composition of hot (proto) neutron star matter. To this end we use a local three-flavor Polyakov–Nambu–Jona-Lasinio model which includes the ’t Hooft (quark flavor mixing) term. It is found that this term leads to non-negligible changes in the particle composition of (proto) neutron stars made of hadron-quark matter. Full article
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Open AccessCommunication
Neutron Star Mass and Radius Measurements
Universe 2019, 5(7), 159; https://doi.org/10.3390/universe5070159
Received: 24 May 2019 / Revised: 19 June 2019 / Accepted: 21 June 2019 / Published: 28 June 2019
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Abstract
Constraints on neutron star masses and radii now come from a variety of sources: theoretical and experimental nuclear physics, astrophysical observations including pulsar timing, thermal and bursting X-ray sources, and gravitational waves, and the assumptions inherent to general relativity and causality of the [...] Read more.
Constraints on neutron star masses and radii now come from a variety of sources: theoretical and experimental nuclear physics, astrophysical observations including pulsar timing, thermal and bursting X-ray sources, and gravitational waves, and the assumptions inherent to general relativity and causality of the equation of state. These measurements and assumptions also result in restrictions on the dense matter equation of state. The two most important structural parameters of neutron stars are their typical radii, which impacts intermediate densities in the range of one to two times the nuclear saturation density, and the maximum mass, which impacts the densities beyond about three times the saturation density. Especially intriguing has been the multi-messenger event GW170817, the first observed binary neutron star merger, which provided direct estimates of both stellar masses and radii as well as an upper bound to the maximum mass. Full article
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Open AccessArticle
Detecting the Hadron-Quark Phase Transition with Gravitational Waves
Universe 2019, 5(6), 156; https://doi.org/10.3390/universe5060156
Received: 22 May 2019 / Revised: 11 June 2019 / Accepted: 12 June 2019 / Published: 20 June 2019
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Abstract
The long-awaited detection of a gravitational wave from the merger of a binary neutron star in August 2017 (GW170817) marks the beginning of the new field of multi-messenger gravitational wave astronomy. By exploiting the extracted tidal deformations of the two neutron stars from [...] Read more.
The long-awaited detection of a gravitational wave from the merger of a binary neutron star in August 2017 (GW170817) marks the beginning of the new field of multi-messenger gravitational wave astronomy. By exploiting the extracted tidal deformations of the two neutron stars from the late inspiral phase of GW170817, it is now possible to constrain several global properties of the equation of state of neutron star matter. However, the most interesting part of the high density and temperature regime of the equation of state is solely imprinted in the post-merger gravitational wave emission from the remnant hypermassive/supramassive neutron star. This regime was not observed in GW170817, but will possibly be detected in forthcoming events within the current observing run of the LIGO/VIRGO collaboration. Numerous numerical-relativity simulations of merging neutron star binaries have been performed during the last decades, and the emitted gravitational wave profiles and the interior structure of the generated remnants have been analysed in detail. The consequences of a potential appearance of a hadron-quark phase transition in the interior region of the produced hypermassive neutron star and the evolution of its underlying matter in the phase diagram of quantum cromo dynamics will be in the focus of this article. It will be shown that the different density/temperature regions of the equation of state can be severely constrained by a measurement of the spectral properties of the emitted post-merger gravitational wave signal from a future binary compact star merger event. Full article
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Open AccessCommunication
Nucleosynthesis and Kilonovae from Strange Star Mergers
Universe 2019, 5(6), 144; https://doi.org/10.3390/universe5060144
Received: 27 March 2019 / Revised: 12 May 2019 / Accepted: 7 June 2019 / Published: 11 June 2019
PDF Full-text (737 KB) | HTML Full-text | XML Full-text
Abstract
In this talk, we summarize the work in progress toward a full characterization of strange star–strange star (SS–SS) mergers related to the GW/GRB/kilonova events. In addition, we show that the a priori probability constructed from the observed neutron star mass distribution points toward [...] Read more.
In this talk, we summarize the work in progress toward a full characterization of strange star–strange star (SS–SS) mergers related to the GW/GRB/kilonova events. In addition, we show that the a priori probability constructed from the observed neutron star mass distribution points toward an asymmetric binary system as the progenitor of the GW170817 event. Full article
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Open AccessCommunication
The Structure of the Hadron-Quark Combustion Zone
Universe 2019, 5(6), 136; https://doi.org/10.3390/universe5060136
Received: 8 May 2019 / Revised: 30 May 2019 / Accepted: 3 June 2019 / Published: 4 June 2019
Cited by 1 | PDF Full-text (292 KB) | HTML Full-text | XML Full-text
Abstract
Hadron-quark combustion in dense matter is a central topic in the study of phases in compact stars and their high-energy astrophysics. We critically reviewed the literature on hadron-quark combustion, dividing them into a “first wave” that treats the problem as a steady-state burning [...] Read more.
Hadron-quark combustion in dense matter is a central topic in the study of phases in compact stars and their high-energy astrophysics. We critically reviewed the literature on hadron-quark combustion, dividing them into a “first wave” that treats the problem as a steady-state burning with or without constraints of mechanical equilibrium, and a “second wave” which uses numerical techniques to resolve the burning front and solves the underlying partial differential equations for the chemistry of the burning front under less restrictive conditions. We detailed the inaccuracies that the second wave amends over the first wave and highlight crucial differences between various approaches in the second wave. We also include results from time-dependent simulations of the reaction zone that include a hadronic EOS, neutrinos, and self-consistent thermodynamics without using parameterized shortcuts. Full article
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Open AccessArticle
Neutron-Star-Merger Equation of State
Universe 2019, 5(5), 129; https://doi.org/10.3390/universe5050129
Received: 31 March 2019 / Revised: 17 May 2019 / Accepted: 22 May 2019 / Published: 25 May 2019
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Abstract
In this work, we discuss the dense matter equation of state (EOS) for the extreme range of conditions encountered in neutron stars and their mergers. The calculation of the properties of such an EOS involves modeling different degrees of freedom (such as nuclei, [...] Read more.
In this work, we discuss the dense matter equation of state (EOS) for the extreme range of conditions encountered in neutron stars and their mergers. The calculation of the properties of such an EOS involves modeling different degrees of freedom (such as nuclei, nucleons, hyperons, and quarks), taking into account different symmetries, and including finite density and temperature effects in a thermodynamically consistent manner. We begin by addressing subnuclear matter consisting of nucleons and a small admixture of light nuclei in the context of the excluded volume approach. We then turn our attention to supranuclear homogeneous matter as described by the Chiral Mean Field (CMF) formalism. Finally, we present results from realistic neutron-star-merger simulations performed using the CMF model that predict signatures for deconfinement to quark matter in gravitational wave signals. Full article
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Open AccessArticle
Equation of State of a Magnetized Dense Neutron System
Universe 2019, 5(5), 104; https://doi.org/10.3390/universe5050104
Received: 26 March 2019 / Revised: 29 April 2019 / Accepted: 30 April 2019 / Published: 6 May 2019
Cited by 1 | PDF Full-text (419 KB) | HTML Full-text | XML Full-text
Abstract
We discuss how a magnetic field can affect the equation of state of a many-particle neutron system. We show that, due to the anisotropy in the pressures, the pressure transverse to the magnetic field direction increases with the magnetic field, while the one [...] Read more.
We discuss how a magnetic field can affect the equation of state of a many-particle neutron system. We show that, due to the anisotropy in the pressures, the pressure transverse to the magnetic field direction increases with the magnetic field, while the one along the field direction decreases. We also show that in this medium there exists a significant negative field-dependent contribution associated with the vacuum pressure. This negative pressure demands a neutron density sufficiently high (corresponding to a baryonic chemical potential of μ = 2.25 GeV) to produce the necessary positive matter pressure that can compensate for the gravitational pull. The decrease of the parallel pressure with the field limits the maximum magnetic field to a value of the order of 10 18 G, where the pressure decays to zero. We show that the combination of all these effects produces an insignificant variation of the system equation of state. We also found that this neutron system exhibits paramagnetic behavior expressed by the Curie’s law in the high-temperature regime. The reported results may be of interest for the astrophysics of compact objects such as magnetars, which are endowed with substantial magnetic fields. Full article
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Open AccessArticle
Questions Related to the Equation of State of High-Density Matter
Universe 2019, 5(5), 100; https://doi.org/10.3390/universe5050100
Received: 27 March 2019 / Revised: 23 April 2019 / Accepted: 24 April 2019 / Published: 30 April 2019
PDF Full-text (288 KB) | HTML Full-text | XML Full-text
Abstract
Astronomical data about neutron stars can be combined with laboratory nuclear data to give us a strong base from which to infer the equation of state of cold catalyzed matter beyond nuclear density. However, the nuclear and astrophysical communities are largely distinct; each [...] Read more.
Astronomical data about neutron stars can be combined with laboratory nuclear data to give us a strong base from which to infer the equation of state of cold catalyzed matter beyond nuclear density. However, the nuclear and astrophysical communities are largely distinct; each has their own methods, which means that there is often imperfect communication between the communities regarding caveats about claimed measurements and constraints. Here we present a brief summary from one astronomer’s perspective of relevant observations of neutron stars, with warnings as appropriate, followed by a set of questions that are intended to help enhance the dialog between nuclear physicists and astrophysicists. Full article
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