Universe: Feature Papers 2024 – Compact Objects

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

Deadline for manuscript submissions: 31 October 2024 | Viewed by 2417

Special Issue Editor


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Institut d’Astronomie et d’Astrophysique, CP-226, Université Libre de Bruxelles, B-1050 Brussels, Belgium
Interests: neutron stars; pulsars; dense matter; quantum condensates; gravitation
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Special Issue Information

Dear Colleagues,

Compact objects, ranging from white dwarfs to neutron stars and black holes, are the most known exotic celestial entities in the universe and manifest themselves through a very large variety of different astrophysical sources and phenomena. Their observations provide a unique testing ground for many branches of theoretical physics, from the properties of matter under extreme conditions experimentally inaccessible on Earth, to the nature of space and time in the strongest gravitational fields. These remnants of stellar evolution also contribute to the origin of heavy elements through nucleosynthesis processes triggered by cataclysmic events such as magnetar giant flares, gravitational core-collapse supernova explosions or binary neutron star mergers.

Over the past few years, the rapid development of multimessenger astronomy, combining various kinds of observations from ground-based optical telescopes to radio telescopes, gravitational-wave interferometers, neutrino detectors and space-based observatories such as X-ray satellites, has brought new insights into compact objects and revealed their different facets.

The aim of this Special Issue is to collect recent advances in the observational and theoretical astrophysics of white dwarfs, neutron stars, black holes and more speculative objects yet to be discovered such as quark stars or dark-matter-admixed neutron stars.

Prof. Dr. Nicolas Chamel
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 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

  • compact object
  • neutron star
  • pulsar
  • magnetar
  • white dwarf
  • black hole
  • X-ray binary

Published Papers (4 papers)

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Research

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18 pages, 967 KiB  
Article
Gravitating Scalarons with Inverted Higgs Potential
by Xiao Yan Chew and Kok-Geng Lim
Universe 2024, 10(5), 212; https://doi.org/10.3390/universe10050212 - 10 May 2024
Viewed by 514
Abstract
Previously, a class of regular and asymptotically flat gravitating scalar solitons (scalarons) has been constructed in the Einstein–Klein–Gordon (EKG) theory by adopting a phantom field with Higgs-like potential where the kinetic term has the wrong sign and the scalaron possesses the negative Arnowitt–Deser–Misner [...] Read more.
Previously, a class of regular and asymptotically flat gravitating scalar solitons (scalarons) has been constructed in the Einstein–Klein–Gordon (EKG) theory by adopting a phantom field with Higgs-like potential where the kinetic term has the wrong sign and the scalaron possesses the negative Arnowitt–Deser–Misner (ADM) mass as a consequence. In this paper, we demonstrate that the use of the phantom field can be avoided by inverting the Higgs-like potential in the EKG system when the kinetic term has a proper sign, such that the corresponding gravitating scalaron can possess the positive ADM mass. We systematically study the basic properties of the gravitating scalaron, such as the ADM mass, the energy conditions, the geodesics of test particles, etc. Moreover, we find that it can be smoothly connected to the counterpart hairy black hole solutions from our recent work in the small horizon limit. Full article
(This article belongs to the Special Issue Universe: Feature Papers 2024 – Compact Objects)
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19 pages, 686 KiB  
Article
Probing the Propeller Regime with Symbiotic X-ray Binaries
by Marina D. Afonina and Sergei B. Popov
Universe 2024, 10(5), 205; https://doi.org/10.3390/universe10050205 - 3 May 2024
Viewed by 497
Abstract
At the moment, there are two neutron star X-ray binaries with massive red supergiants as donors. Recently, De et al. (2023) proposed that the system SWIFT J0850.8-4219 contains a neutron star at the propeller stage. We study this possibility by applying various models [...] Read more.
At the moment, there are two neutron star X-ray binaries with massive red supergiants as donors. Recently, De et al. (2023) proposed that the system SWIFT J0850.8-4219 contains a neutron star at the propeller stage. We study this possibility by applying various models of propeller spin-down. We demonstrate that the duration of the propeller stage is very sensitive to the regime of rotational losses. Only in the case of a relatively slow propeller model proposed by Davies and Pringle in 1981, the duration of the propeller is long enough to provide a significant probability to observe the system at this stage. Future determination of the system parameters (orbital and spin periods, magnetic field of the compact object, etc.) will allow putting strong constraints on the propeller behavior. Full article
(This article belongs to the Special Issue Universe: Feature Papers 2024 – Compact Objects)
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18 pages, 2427 KiB  
Article
Linear Stability Analysis of Relativistic Magnetized Jets: The Minimalist Approach
by Nektarios Vlahakis
Universe 2024, 10(4), 183; https://doi.org/10.3390/universe10040183 - 17 Apr 2024
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Abstract
A minimalist approach to the linear stability problem in fluid dynamics is developed that ensures efficiency by utilizing only the essential elements required to find the eigenvalues for given boundary conditions. It is shown that the problem is equivalent to a single first-order [...] Read more.
A minimalist approach to the linear stability problem in fluid dynamics is developed that ensures efficiency by utilizing only the essential elements required to find the eigenvalues for given boundary conditions. It is shown that the problem is equivalent to a single first-order ordinary differential equation, and that studying the argument of the unknown complex function in the eigenvalue space is sufficient to find the dispersion relation. The method is applied to a model for relativistic magnetized astrophysical jets. Full article
(This article belongs to the Special Issue Universe: Feature Papers 2024 – Compact Objects)
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Review

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34 pages, 7190 KiB  
Review
Magnetar QPOs and Neutron Star Crust Elasticity
by Hajime Sotani
Universe 2024, 10(6), 231; https://doi.org/10.3390/universe10060231 - 22 May 2024
Viewed by 201
Abstract
The crust region is a tiny fraction of neutron stars, but it has a variety of physical properties and plays an important role in astronomical observations. One of the properties characterizing the crust is elasticity. In this review, with the approach of asteroseismology, [...] Read more.
The crust region is a tiny fraction of neutron stars, but it has a variety of physical properties and plays an important role in astronomical observations. One of the properties characterizing the crust is elasticity. In this review, with the approach of asteroseismology, we systematically examine neutron star oscillations excited by crust elasticity, adopting the Cowling approximation. In particular, by identifying the quasi-periodic oscillations observed in magnetar flares with the torsional oscillations, we make a constraint on the nuclear saturation parameters. In addition, we also discuss how the shear and interface modes depend on the neutron star properties. Once one detects an additional signal associated with neutron star oscillations, one can obtain a more severe constraint on the saturation parameters and/or neutron star properties, which must be a qualitatively different constraint obtained from terrestrial experiments and help us to complementarily understand astrophysics and nuclear physics. Full article
(This article belongs to the Special Issue Universe: Feature Papers 2024 – Compact Objects)
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