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

Deadline for manuscript submissions: closed (31 July 2021) | Viewed by 11549

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Special Issue Editors

Prof. Dr. Francesco De Paolis

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Guest Editor

1. Dipartimento di Matematica e Fisica “Ennio De Giorgi”, Università del Salento, CP 193, I-73100 Lecce, Italy
2. INFN, Sezione di Lecce, Via per Arnesano I-73100 Lecce, Italy
Interests: gravitational lensing; relativistic astrophysics
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Alexander F. Zakharov

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Guest Editor

Institute of Theoretical and Experimental Physics, B. Cheremushkinskaya, 25, Moscow 117218, Russia
Interests: black holes; gravitational lensing; cosmology
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Achille Nucita

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Guest Editor

1. Department of Mathematics and Physics “E. De Giorgi”, University of Salento, Via per Arnesano I-73100 Lecce, Italy
2. INFN, Sezione di Lecce, Via per Arnesano I-73100 Lecce, Italy
Interests: theoretical astrophysics; high energy astrophysics

Special Issue Information

Dear Colleagues,

Relativistic Astrophysics is the branch of astrophysics that studies astronomical phenomena and celestial bodies, for which classical mechanics and Newton’s law of gravitation are inapplicable. The field of relativistic astrophysics began with Schwarzschild’s solution and still continues to grow very rapidly, a century on since the birth of general relativity theory. In the last few years, two epochal confirmations of general relativity have finally been achieved: The discovery of gravitational waves from merging massive black holes and neutron stars, and the first image of the supermassive black hole in the center of the M87 galaxy by the EHT set of instruments. In spite of the enormous progresses obtained in recent years, however, and mainly due to new observation facilities, many questions remain open, and many queries have been raised by observations.

The main aim of this Special Issue is to review recent progress in the field of relativistic astrophysics and to point out future perspectives. All submissions will be peer reviewed before being accepted for publication.

Prof. Dr. Francesco De Paolis
Prof. Dr. Alexander F. Zakharov
Prof. Dr. Achille Nucita
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

high-energy astrophysics
astrophysics of black holes and neutron stars
gravitational waves
astro-physical tests of general relativity
relativistic astrophysics.

Published Papers (5 papers)

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Editorial

Jump to: Research

2 pages, 171 KiB

Open AccessEditorial

Editorial for the Special Issue “Relativistic Astrophysics”

by Francesco De Paolis, Achille A. Nucita and Alexander F. Zakharov

Universe 2022, 8(1), 29; https://doi.org/10.3390/universe8010029 - 04 Jan 2022

Viewed by 819

Abstract

Relativistic Astrophysics is the branch of astrophysics that studies astronomical phenomena and celestial bodies, for which classical mechanics and Newton’s law of gravitation are inapplicable to creation of suitable models and we have to generalize these approaches following general relativistic prescriptions [...] Full article

(This article belongs to the Special Issue Relativistic Astrophysics)

Research

Jump to: Editorial

13 pages, 661 KiB

Open AccessArticle

Stable Wormholes in the Background of an Exponential f(R) Gravity

by Ghulam Mustafa, Ibrar Hussain and M. Farasat Shamir

Universe 2020, 6(4), 48; https://doi.org/10.3390/universe6040048 - 26 Mar 2020

Cited by 16 | Viewed by 2287

Abstract

The current paper is devoted to investigating wormhole solutions with an exponential gravity model in the background of

f (R)

theory. Spherically symmetric static spacetime geometry is chosen to explore wormhole solutions with anisotropic fluid source. The behavior of the traceless [...] Read more.

The current paper is devoted to investigating wormhole solutions with an exponential gravity model in the background of

f (R)

theory. Spherically symmetric static spacetime geometry is chosen to explore wormhole solutions with anisotropic fluid source. The behavior of the traceless matter is studied by employing a particular equation of state to describe the important properties of the shape-function of the wormhole geometry. Furthermore, the energy conditions and stability analysis are done for two specific shape-functions. It is seen that the energy condition are to be violated for both of the shape-functions chosen here. It is concluded that our results are stable and realistic. Full article

(This article belongs to the Special Issue Relativistic Astrophysics)

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20 pages, 1677 KiB

Open AccessArticle

Magnetized Particle Motion around Black Holes in Conformal Gravity: Can Magnetic Interaction Mimic Spin of Black Holes?

by Kamoliddin Haydarov, Ahmadjon Abdujabbarov, Javlon Rayimbaev and Bobomurat Ahmedov

Universe 2020, 6(3), 44; https://doi.org/10.3390/universe6030044 - 17 Mar 2020

Cited by 27 | Viewed by 2343

Abstract

Magnetized particle motion around black holes in conformal gravity immersed in asymptotically uniform magnetic field has been studied. We have also analyzed the behavior of magnetic fields near the horizon of the black hole in conformal gravity and shown that with the increase of conformal parameters L and N the value of angular component of magnetic field at the stellar surface decreases. The maximum value of the effective potential corresponding to circular motion of the magnetized particle increases with the increase of conformal parameters. It is shown that in all cases of neutral, charged and magnetized particle collisions in the black hole environment the center-of-mass energy decreases with the increase of conformal parameters L and N. In the case of the magnetized and negatively charged particle collisions, the innermost collision point with the maximum center-of-mass energy comes closer to the central object due to the effects of the parameters of the conformal gravity. We have applied the results to the real astrophysical scenario when a pulsar treated as a magnetized particle is orbiting the super massive black hole (SMBH) Sgr A* in the center of our galaxy in order to obtain the estimation of magnetized compact object’s orbital parameter. The possible detection of pulsar in Sgr A* close environment can provide constraints on black hole parameters. Here we have shown that there is degeneracy between spin of SMBH and ambient magnetic field and consequently the interaction of magnetic field

\sim 10^{2}

Gauss with magnetic moment of magnetized neutron star can in principle mimic spin of Kerr black holes up to

0.6

. Full article

(This article belongs to the Special Issue Relativistic Astrophysics)

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8 pages, 364 KiB

Open AccessArticle

β⁻-Decay Half-Lives of Even-Even Nuclei Using the Recently Introduced Phase Space Recipe

by Jameel-Un Nabi, Mavra Ishfaq, Ovidiu Niţescu, Mihail Mirea and Sabin Stoica

Universe 2020, 6(1), 5; https://doi.org/10.3390/universe6010005 - 26 Dec 2019

Cited by 1 | Viewed by 2608

Abstract

In this paper, we present the

β

-decay half-lives calculation for selected even-even nuclei that decay through electron emission. The kinematical portion of the half-life calculation was performed using a recently introduced technique for computation of phase space factors (PSFs). The dynamical portion [...] Read more.

In this paper, we present the

β

^{20}

^{24}

Ne,

^{34}

Si,

^{54}

Ti,

^{62}

Fe and

^{98}

Zr) were selected for the present calculation. We compare the calculated PSFs for these cases against the traditionally used recipe. In our new approach, the Dirac equation was numerically solved by employing a Coulomb potential. This potential was adopted from a more realistic proton distribution of the daughter nucleus. Thus, the finite size of the nucleus and the diffuse nuclear surface corrections are taken into account. Moreover, a screened Coulomb potential was constructed to account for the effect of atomic screening. The power series technique was used for the numerical solution. The calculated values of half-lives, employing the recently developed method for computation of PSFs, were in good agreement with the experimental data. Full article

(This article belongs to the Special Issue Relativistic Astrophysics)

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22 pages, 2089 KiB

Open AccessArticle

Dynamical Stability of Bulk Viscous Isotropic and Homogeneous Universe

by Muhammad Sharif and Qanitah Ama-Tul-Mughani

Universe 2019, 5(8), 185; https://doi.org/10.3390/universe5080185 - 09 Aug 2019

Cited by 2 | Viewed by 2405

Abstract

In this paper, we study the phase space portrait of homogeneous and isotropic universe by taking different coupling functions between dark energy models and bulk viscous dark matter. The dimensionless quantities are introduced to establish an autonomous set of equations. To analyze the stability of the cosmos, we evaluate critical points and respective eigenvalues for different dynamical quantities. For bulk viscous matter and radiation in tachyon coupled field, these points show stable evolution when

γ ≫ δ

but accelerated expansion of the universe for

δ > \frac{1}{9}

. The stability of the universe increases for some stationary points which may correspond to the late-time expansion for the coupled phantom field. Full article

(This article belongs to the Special Issue Relativistic Astrophysics)

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