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

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

Deadline for manuscript submissions: closed (8 May 2019) | Viewed by 36868

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Special Issue Editors

Prof. Vivian De la Incera

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Guest Editor

City University of New York/College of Staten Island, New York 10314, USA
Interests: QCD phases; external field effects; transport in dense matter

Prof. Efrain Ferrer

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Guest Editor

City University of New York/College of Staten Island, New York 10314, USA
Interests: QCD under extreme conditions; Equation of state in neutron stars

Prof. Jim Lattimer

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Guest Editor

State University of New York at Stony Brook, Stony Brook, NY 11794, USA
Interests: neutron star cooling; supernovae explosions; properties of hot; dense matter; binary mergers

Prof. Dr. David Blaschke

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Guest Editor

1. Institute of Theoretical Physics, University of Wroclaw, 50-204 Wroclaw, Poland
2. Center for Advanced Systems Understanding (CASUS), D-02826 Görlitz, Germany
3. Helmholtz-Zentrum Dresden-Rossendorf (HZDR), D-1328 Dresden, Germany
Interests: quantum field theory; quantum statistics; quark gluon plasma; heavy ion collisions; compact stars
Special Issues, Collections and Topics in MDPI journals

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 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

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

Published Papers (13 papers)

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Research

22 pages, 3003 KiB

Open AccessEditor’s ChoiceArticle

Was GW170817 a Canonical Neutron Star Merger? Bayesian Analysis with a Third Family of Compact Stars

by David Blaschke, Alexander Ayriyan, David Edwin Alvarez-Castillo and Hovik Grigorian

Universe 2020, 6(6), 81; https://doi.org/10.3390/universe6060081 - 10 Jun 2020

Cited by 63 | Viewed by 3756

Abstract

We investigate the possibility that GW170817 was not the merger of two conventional neutron stars (NS), but involved at least one if not two hybrid stars with a quark matter core that might even belong to a third family of compact stars. To this end, we develop a Bayesian analysis method for selecting the most probable equation of state (EoS) under a set of constraints from compact star physics, which now also include the tidal deformability from GW170817 and the first result for the mass and radius determination for PSR J0030+0451 by the NICER Collaboration. We apply this method for the first time to a two-parameter family of hybrid EoS based on the DD2 model with nucleonic excluded volume for hadronic matter and the color superconducting generalized nlNJL model for quark matter. The model has a variable onset density for deconfinement and can mimic the effects of pasta phases with the possibility of producing a third family of hybrid stars in the mass-radius diagram. The main findings of this study are that: (1) the presence of multiple configurations for a given mass (twins or even triples) corresponds to a set of disconnected lines in the

Λ_{1}

–

Λ_{2}

diagram of tidal deformabilities for binary mergers, so that merger events from the same mass range may result in a probability landscape with different peak positions; (2) the Bayesian analysis with the above observational constraints favors an early onset of the deconfinement transition, at masses of

M_{onset} \leq 0.8 M_{⊙}

with an M–R relationship that in the range of observed neutron star masses is almost indistinguishable from that of a soft hadronic Akmal, Pandharipande, and Ravenhall (APR) EoS; (3) a few, yet fictitious measurements of the NICER experiment two times more accurate than the present value and a different mass and radius that would change the posterior likelihood so that hybrid EoS with a phase transition onset in the range

M_{onset}

= 1.1–1.6

M_{⊙}

would be favored. Full article

(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram and in the Multi-Messenger Era of Astronomy)

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Graphical abstract

10 pages, 336 KiB

Open AccessArticle

Constraints on Microscopic and Phenomenological Equations of State of Dense Matter from GW170817

by Domenico Logoteta and Ignazio Bombaci

Universe 2019, 5(10), 204; https://doi.org/10.3390/universe5100204 - 25 Sep 2019

Cited by 3 | Viewed by 2587

Abstract

We discuss the constraints on the equation of state (EOS) of neutron star matter obtained by the data analysis of the neutron star-neutron star merger in the event GW170807. To this scope, we consider two recent microscopic EOS models computed starting from two-body and three-body nuclear interactions derived using chiral perturbation theory. For comparison, we also use three representative phenomenological EOS models derived within the relativistic mean field approach. For each model, we determine the

β

-stable EOS and then the corresponding neutron star structure by solving the equations of hydrostatic equilibrium in general relativity. In addition, we calculate the tidal deformability parameters for the two neutron stars and discuss the results of our calculations in connection with the constraints obtained from the gravitational wave signal in GW170817. We find that the tidal deformabilities and radii for the binary’s component neutron stars in GW170817, calculated using a recent microscopic EOS model proposed by the present authors, are in very good agreement with those derived by gravitational waves data. Full article

(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram and in the Multi-Messenger Era of Astronomy)

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12 pages, 612 KiB

Open AccessArticle

Identifying Quark Matter in Hybrid Stars through Relativistic Tidal Deformations

by Bryen Irving, Thomas Klähn, Prashanth Jaikumar, Marc Salinas and Wei Wei

Universe 2019, 5(9), 193; https://doi.org/10.3390/universe5090193 - 30 Aug 2019

Cited by 2 | Viewed by 2902

Abstract

We study a specific model of neutron star matter that supports a phase transition to quark matter at high density and examine parameter ranges for consistency with the mass-weighted tidal deformability of

\tilde{Λ} = 300_{- 230}^{+ 420}

for a mass [...] Read more.

\tilde{Λ} = 300_{- 230}^{+ 420}

for a mass ratio of

q \in [0.73, 1.0]

, as inferred from observations of gravitational waves from the binary neutron star merger event GW170817. By using this observation to restrict the parameter space for the equation of state (EoS) model used throughout this study, we aim to assess the possibility of a potential solution to the masquerade and flavor camouflage problems for hybrid EoS models. Assuming the two stars have the same EoS, in which the Dirac-Brueckner-Hartree Fock (DBHF) nuclear model transitions to the vBag quark model, we see if the parameter space of these hybrid model stars are restricted due to the adherence to the reported

Λ_{1.4} \in [70, 580]

and

M_{m a x} \in [2.01, 2.16] M_{⊙}

constraints. Upon completion, we find that, while the parameter space for our model does get restricted, it does not ultimately resolve the masquerade and flavor camouflage problems. Full article

(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram and in the Multi-Messenger Era of Astronomy)

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12 pages, 437 KiB

Open AccessArticle

Impact of the Nuclear Equation of State on the Stability of Hybrid Neutron Stars

by Mateusz Cierniak, Tobias Fischer, Niels-Uwe Bastian, Thomas Klähn and Marc Salinas

Universe 2019, 5(8), 186; https://doi.org/10.3390/universe5080186 - 12 Aug 2019

Cited by 9 | Viewed by 2717

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 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

(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram and in the Multi-Messenger Era of Astronomy)

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13 pages, 1030 KiB

Open AccessArticle

Parity Doubling and the Dense-Matter Phase Diagram under Constraints from Multi-Messenger Astronomy

by Michał Marczenko, David Blaschke, Krzysztof Redlich and Chihiro Sasaki

Universe 2019, 5(8), 180; https://doi.org/10.3390/universe5080180 - 30 Jul 2019

Cited by 25 | Viewed by 2250

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 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

(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram and in the Multi-Messenger Era of Astronomy)

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17 pages, 1008 KiB

Open AccessArticle

Phases of Hadron-Quark Matter in (Proto) Neutron Stars

by Fridolin Weber, Delaney Farrell, William M. Spinella, Germán Malfatti, Milva G. Orsaria, Gustavo A. Contrera and Ian Maloney

Universe 2019, 5(7), 169; https://doi.org/10.3390/universe5070169 - 11 Jul 2019

Cited by 12 | Viewed by 2818

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. 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

(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram and in the Multi-Messenger Era of Astronomy)

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20 pages, 10546 KiB

Open AccessCommunication

Neutron Star Mass and Radius Measurements

by James M. Lattimer

Universe 2019, 5(7), 159; https://doi.org/10.3390/universe5070159 - 28 Jun 2019

Cited by 44 | Viewed by 4810

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 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

(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram and in the Multi-Messenger Era of Astronomy)

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12 pages, 6922 KiB

Open AccessArticle

Detecting the Hadron-Quark Phase Transition with Gravitational Waves

by Matthias Hanauske, Luke Bovard, Elias Most, Jens Papenfort, Jan Steinheimer, Anton Motornenko, Volodymyr Vovchenko, Veronica Dexheimer, Stefan Schramm and Horst Stöcker

Universe 2019, 5(6), 156; https://doi.org/10.3390/universe5060156 - 20 Jun 2019

Cited by 14 | Viewed by 2879

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 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

(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram and in the Multi-Messenger Era of Astronomy)

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7 pages, 737 KiB

Open AccessCommunication

Nucleosynthesis and Kilonovae from Strange Star Mergers

by J. E. Horvath, O. G. Benvenuto, E. Bauer, L. Paulucci, A. Bernardo and H. R. Viturro

Universe 2019, 5(6), 144; https://doi.org/10.3390/universe5060144 - 11 Jun 2019

Cited by 4 | Viewed by 2019

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.

(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram and in the Multi-Messenger Era of Astronomy)

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9 pages, 292 KiB

Open AccessCommunication

The Structure of the Hadron-Quark Combustion Zone

by Amir Ouyed, Rachid Ouyed and Prashanth Jaikumar

Universe 2019, 5(6), 136; https://doi.org/10.3390/universe5060136 - 04 Jun 2019

Cited by 3 | Viewed by 2026

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 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

(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram and in the Multi-Messenger Era of Astronomy)

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9 pages, 1792 KiB

Open AccessArticle

Neutron-Star-Merger Equation of State

by Veronica Dexheimer, Constantinos Constantinou, Elias R. Most, L. Jens Papenfort, Matthias Hanauske, Stefan Schramm, Horst Stoecker and Luciano Rezzolla

Universe 2019, 5(5), 129; https://doi.org/10.3390/universe5050129 - 25 May 2019

Cited by 7 | Viewed by 2596

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, 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

(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram and in the Multi-Messenger Era of Astronomy)

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14 pages, 419 KiB

Open AccessArticle

Equation of State of a Magnetized Dense Neutron System

by Efrain J. Ferrer and Aric Hackebill

Universe 2019, 5(5), 104; https://doi.org/10.3390/universe5050104 - 06 May 2019

Cited by 9 | Viewed by 2137

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 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

(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram and in the Multi-Messenger Era of Astronomy)

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11 pages, 288 KiB

Open AccessArticle

by M. Coleman Miller

Universe 2019, 5(5), 100; https://doi.org/10.3390/universe5050100 - 30 Apr 2019

Cited by 2 | Viewed by 2274

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 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

(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram and in the Multi-Messenger Era of Astronomy)

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