Microphysics Meets Astrophysics: Understanding Dense Matter Through Compact Objects

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

Deadline for manuscript submissions: 31 October 2026 | Viewed by 3605

Special Issue Editors


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Guest Editor
1. Grupo de Astrofísica de Remanentes Compactos, Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, La Plata, Argentina
2. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), La Plata, Argentina
Interests: hybrid stars; dense matter; equation of state; hadron-quark phase transition; non-radial oscillations of compact stars; gravitational waves

E-Mail Website
Guest Editor
1. Grupo de Astrofísica de Remanentes Compactos, Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, La Plata, Argentina
2. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), La Plata, Argentina
Interests: theoretical astrophysics; neutron stars; hybrid stars; dense matter; equation of state; non-radial oscillations of compact stars; gravitational waves

Special Issue Information

Dear Colleagues,

Neutron stars are amongst the most extreme objects in the Universe. Hence, these objects can be regarded as natural laboratories in which matter is subject to the most extreme conditions. The matter at the innermost part of their cores can reach values that are over tens of the nuclear saturation density, potentially leading to the occurrence of a hadron–quark phase transition; their magnetic fields can reach above 1015 G at their surfaces. Moreover, some neutron stars rotate more than 1000 times per second. These objects are thus complex and intriguing, and enable us to understand the very nature of particles and the equation of state of dense matter, which remains unknown.

The open access journal Symmetry is launching a new Special Issue entitled "Microphysics Meets Astrophysics: Understanding Dense Matter Through Compact Objects". It aims to provide an overview of research regarding the theoretical modeling and study of neutron and hybrid stars microphysics and astrophysics. In the current era of multi-messenger astronomy using gravitational waves, which began with event GW170817, and the application of data science to basic research, this Special Issue aims to present novel studies that explore these subjects.

We welcome the submission of both original articles or review papers. Please submit your paper to the Special Issue of Symmetry entitled “Microphysics Meets Astrophysics: Understanding Dense Matter Through Compact Objects”, via the MDPI submission system. The papers will be peer-reviewed by specialists before being published immediately after acceptance.

We look forward to receiving your submissions.

Dr. Ignacio Francisco Ranea-Sandoval
Dr. Mauro Mariani
Guest Editors

Manuscript Submission Information

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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 2400 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
  • hybrid stars
  • equation of state
  • dense matter
  • gravitational waves
  • hadron–quark phase transition
  • non-radial oscillation modes
  • dark matter in compact objects
  • quark stars

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Published Papers (3 papers)

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Research

14 pages, 869 KB  
Article
Role of Dark Matter in the Dynamics of Compact-Object Binaries
by Carlos R. Argüelles, Valentina Crespi, José Fernando Rodríguez-Ruiz and Jorge A. Rueda
Symmetry 2026, 18(3), 484; https://doi.org/10.3390/sym18030484 - 12 Mar 2026
Viewed by 437
Abstract
The orbital dynamics of compact-object binaries composed of neutron stars (NSs) and white dwarfs (WDs) can be influenced by the gravitational interaction with the gas of dark matter (DM) particles, generating dynamical friction. We discuss the orbital dynamics of detached binaries, quantifying the [...] Read more.
The orbital dynamics of compact-object binaries composed of neutron stars (NSs) and white dwarfs (WDs) can be influenced by the gravitational interaction with the gas of dark matter (DM) particles, generating dynamical friction. We discuss the orbital dynamics of detached binaries, quantifying the effect of dynamical friction from DM relative to that driven solely by gravitational-wave emission in vacuum. We focus on fermionic DM within the Ruffini–Arguelles–Rueda (RAR) model, for a fermion of rest-mass in the range 56–300 keV. We find that, for NS-NS, NS-WD, and WD-WD with parameters similar to those of J0737-3039, J0348+0432, and J0651+2844, the DM dynamical friction becomes detectable by space-based GW interferometers such as LISA and TianQin for binaries within a few milliparsec from the Galactic center, and could even dominate the orbital dynamics. Full article
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24 pages, 666 KB  
Article
How Neutron Star Observations Point Towards Exotic Matter: Existing Explanations and a Prospective Proposal
by Mauro Mariani and Ignacio F. Ranea-Sandoval
Symmetry 2026, 18(1), 27; https://doi.org/10.3390/sym18010027 - 23 Dec 2025
Viewed by 1078
Abstract
Multi-messenger astronomical observations of neutron stars, together with more precise calculations and constraints coming from dense matter microphysics, are generating tension with regard to equations of state models used to describe neutron star cores. Assuming an abrupt first-order phase transition with a slow [...] Read more.
Multi-messenger astronomical observations of neutron stars, together with more precise calculations and constraints coming from dense matter microphysics, are generating tension with regard to equations of state models used to describe neutron star cores. Assuming an abrupt first-order phase transition with a slow conversion speed between phases, we propose different slow stable hybrid star configurations aiming to reconcile all current constraints simultaneously; within this framework, we also introduce a novel non-CSS parametrization to the quark matter equation of state and discuss its strengths and limitations. We analyze our model results in conjunction with a review of other relevant theoretical possibilities existing in the literature. We found that modern neutron star observations seem to favor the existence of some type of exotic matter in the neutron star cores; in particular, our slow stable hybrid star scenario remains a proposal capable of satisfying these constraints. However, due both to the existing skepticism regarding some of the adopted hypotheses in most extreme neutron star measurements and to the precise adjustment needed for the equation-of-state parameters, significant tension and open questions remain. Full article
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15 pages, 3582 KB  
Article
Illuminating Dark Matter Admixed in Neutron Stars with Simultaneous Mass–Radius Constraints
by Naibo Zhang, Bao-An Li, Jiayu Zhang, Weina Shen and Hui Zhang
Symmetry 2025, 17(10), 1669; https://doi.org/10.3390/sym17101669 - 6 Oct 2025
Cited by 4 | Viewed by 1444
Abstract
We investigate how simultaneous mass and radius measurements of massive neutron stars can help constrain the properties of dark matter possibly admixed in them. Within a fermionic dark matter model that interacts only through gravitation, along with a well-constrained nuclear matter equation of [...] Read more.
We investigate how simultaneous mass and radius measurements of massive neutron stars can help constrain the properties of dark matter possibly admixed in them. Within a fermionic dark matter model that interacts only through gravitation, along with a well-constrained nuclear matter equation of state, we show that the simultaneous mass and radius measurement of PSRJ0740+6620 reduces the uncertainty of dark matter central energy density by more than 50% compared to the results obtained from using the two observables independently, while other dark matter parameters remain unconstrained. Additionally, we find that the dark matter fraction fD should be smaller than 2% when constrained by the observed neutron star maximum mass alone, and it could be even smaller than 0.3% with the simultaneous measurement of mass and radius, supporting the conclusion that only a small amount of dark matter exists in dark matter admixed neutron stars (DANSs). Full article
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