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A special issue of Galaxies (ISSN 2075-4434).

Deadline for manuscript submissions: closed (31 July 2023) | Viewed by 10504

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Dr. Zeeshan Yousaf

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Guest Editor

Department of Mathematics, University of the Punjab, Quaid-i-Azam Campus, Lahore 54590, Pakistan
Interests: mathematical physics; geometry; stellar dynamics; self-gravitating systems; gravitational theories
Special Issues, Collections and Topics in MDPI journals

Dr. Kazuharu Bamba

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Guest Editor

Faculty of Symbiotic Systems Science, Fukushima University, Fukushima 960-1296, Japan
Interests: particle cosmology; gravity theory; inflation; late time acceleration
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Dr. M. Z. Bhatti

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Guest Editor

Department of Mathematics, University of the Punjab, Quaid-i-Azam Campus, Lahore 54590, Pakistan
Interests: geometry; nonlinear analysis; theoretical and mathematical physics; relativistic astrophysics; cosmology
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Special Issue Information

Dear Colleagues,

This Special Issue welcomes original research articles that focus on the analysis of astrophysical objects in the context of Extended Gravity Theories. We also welcome the paper related to numerical simulations of linear and non-linear dynamical systems. We are hoping to attract studies regarding the possible attainment of high masses of neutron stars and white dwarfs from the Extended Gravity Theories perspective. Moreover, the question of whether it is possible to obtain nonexotic matter wormhole solutions in these theories is expected to be addressed. The physical consequences of studying black holes, strange stars, and gravastars in Extended Gravity Theories are also welcome. The purpose of this special issue is to compile original findings with an emphasis on numerical and theoretical challenges in dynamical systems. Review articles on the current state of the art are also invited.

Traditional formulations or more recent methods based on compartmental models, dynamic networking systems, multi-scale problems, linear and nonlinear differential equations, fractional differential equations and Hamiltonian dynamic evolutions are all welcome. We also expect to receive review articles describing the current state-of-the-art within this broad subject. Potential topics include but are not limited to the following:

Astrophysics and Astroparticle Physics

Astronomical observations; cosmological implications of the God particle; dark matter astrophysics; dark energy; electromagnetic process and properties; fundamental aspects of astrophysics; high-energy astrophysics/astroparticle; relativistic stars, structure, stability and oscillation—other topics.

Cosmology

Cosmic acceleration; cosmic microwave background radiation; inhomogeneous exact cosmologies; large scale structures; mathematical and relativistic aspects of cosmology; observational cosmology including the Hubble constant, distance scale, cosmological constant, early universe; theoretical cosmology—other topics.

Compact Objects

Black holes, mergers and accretion disks; galaxy evolution; measurements common to several branches of physics and astronomy; neutron stars; self-gravitating systems; strong gravitational lensing—other topics.

General Relativity and Modified Gravity Theories

Alternative theories of gravity; classical general relativity; numerical studies of critical behavior, singularities and cosmic censorship; strong-field tests of general relativity—other topics.

Non-linear Analysis

Non-linear analysis in mathematics, physics, biology, chemistry, engineering, economics, history, and medicine; dynamical systems; linear dynamic system; nonlinear dynamic system; theoretical challenges in differetial calculus; numerical methods; fractional differential equations.

Dr. Zeeshan Yousaf
Dr. Kazuharu Bamba
Dr. M. Z. Bhatti
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. Galaxies is an international peer-reviewed open access semimonthly 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 1400 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

astrophysics and astroparticle physics
cosmology
compact objects
general relativity and modified gravity theories

Published Papers (4 papers)

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Research

11 pages, 296 KiB

Open AccessArticle

On the Periodic Orbits of the Perturbed Two- and Three-Body Problems

by Elbaz I. Abouelmagd, Juan Luis García Guirao and Jaume Llibre

Galaxies 2023, 11(2), 58; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies11020058 - 18 Apr 2023

Cited by 3 | Viewed by 1419

Abstract

In this work, a perturbed system of the restricted three-body problem is derived when the perturbation forces are conservative alongside the corresponding mean motion of two primaries bodies. Thus, we have proved that the first and second types of periodic orbits of the rotating Kepler problem can persist for all perturbed two-body and circular restricted three-body problems when the perturbation forces are conservative or the perturbed motion has its own extended Jacobian integral. Full article

(This article belongs to the Special Issue Relativistic Cosmology, Numerical Analysis, General Relativity and Modified Gravity Theories)

17 pages, 538 KiB

Open AccessArticle

The Simplest Parametrization of the Equation of State Parameter in the Scalar Field Universe

by Preeti Shrivastava, Abdul Junaid Khan, Mukesh Kumar, Gopikant Goswami, Jainendra Kumar Singh and Anil Kumar Yadav

Galaxies 2023, 11(2), 57; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies11020057 - 17 Apr 2023

Cited by 10 | Viewed by 1538

Abstract

In this paper, we investigate a scalar field cosmological model of accelerating Universe with the simplest parametrization of the equation of state parameter of the scalar field. We use

H (z)

data, pantheon compilation of SN Ia data and BAO data [...] Read more.

In this paper, we investigate a scalar field cosmological model of accelerating Universe with the simplest parametrization of the equation of state parameter of the scalar field. We use

H (z)

data, pantheon compilation of SN Ia data and BAO data to constrain the model parameters using the

χ^{2}

minimization technique. We obtain the present values of Hubble constant

H_{0}

66 . 2_{- 1.34}^{+ 1.42}

70 . 7_{- 0.31}^{+ 0.32}

and

67 . 74_{- 1.04}^{+ 1.24}

for

H (z)

H (z)

+ Pantheon and

H (z)

+ BAO respectively. In addition, we estimate the present age of the Universe in a derived model

t_{0} = 14 . 38_{- 0.64}^{+ 0.63}

for joint

H (z)

and pantheon compilation of SN Ia data which has only

0.88 σ

tension with its empirical value obtained in Plank collaboration. Moreover, the present values of the deceleration parameter

q_{0}

come out to be

- 0 . 55_{- 0.038}^{+ 0.031}

- 0 . 61_{- 0.021}^{+ 0.030}

and

- 0 . 627_{- 0.025}^{+ 0.022}

by bounding the Universe in the derived model with

H (z)

H (z)

+ Pantheon compilation of SN Ia and

H (z)

+ BAO data sets, respectively. We also have performed the state-finder diagnostics to discover the nature of dark energy. Full article

(This article belongs to the Special Issue Relativistic Cosmology, Numerical Analysis, General Relativity and Modified Gravity Theories)

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Figure 1

14 pages, 4984 KiB

Open AccessArticle

The Effects of Inertial Forces on the Dynamics of Disk Galaxies

by Roy Gomel and Tomer Zimmerman

Galaxies 2021, 9(2), 34; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9020034 - 13 May 2021

Cited by 2 | Viewed by 3515

Abstract

When dealing with galactic dynamics, or more specifically, with galactic rotation curves, one basic assumption is always taken: the frame of reference relative to which the rotational velocities are given is assumed to be inertial. In other words, fictitious forces are assumed to vanish relative to the observational frame of a given galaxy. It might be interesting, however, to explore the outcomes of dropping that assumption; that is, to search for signatures of non-inertial behavior in the observed data. In this work, we show that the very discrepancy in galaxy rotation curves could be attributed to non-inertial effects. We derive a model for spiral galaxies that takes into account the possible influence of fictitious forces and find that the additional terms in the new model, due to fictitious forces, closely resemble dark halo profiles. Following this result, we apply the new model to a wide sample of galaxies, spanning a large range of luminosities and radii. It turns out that the new model accurately reproduces the structures of the rotation curves and provides very good fittings to the data. Full article

(This article belongs to the Special Issue Relativistic Cosmology, Numerical Analysis, General Relativity and Modified Gravity Theories)

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Figure 1

20 pages, 850 KiB

Open AccessArticle

Magnetized Particle Motion in γ-Spacetime in a Magnetic Field

by Ahmadjon Abdujabbarov, Javlon Rayimbaev, Farruh Atamurotov and Bobomurat Ahmedov

Galaxies 2020, 8(4), 76; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies8040076 - 29 Oct 2020

Cited by 20 | Viewed by 2451

Abstract

In the present work we explored the dynamics of magnetized particles around the compact object in

γ

-spacetime in the presence of an external asymptotically-uniform magnetic field. The analysis of the circular orbits of magnetized particles around the compact object in the spacetime [...] Read more.

In the present work we explored the dynamics of magnetized particles around the compact object in

γ

-spacetime in the presence of an external asymptotically-uniform magnetic field. The analysis of the circular orbits of magnetized particles around the compact object in the spacetime of a

γ

-object immersed in the external magnetic field has shown that the area of stable circular orbits of magnetized particles increases with the increase of

γ

-parameter. We have also investigated the acceleration of the magnetized particles near the

γ

-object and shown that the center-of-mass energy of colliding magnetized particles increases with the increase of

γ

-parameter. Finally, we have applied the obtained results to the astrophysical scenario and shown that the values of

γ

-parameter in the range of

γ \in (0.5, 1)

can mimic the spin of Kerr black hole up to

a ≃ 0.85

, while the magnetic interaction can mimic the

γ

-parameter at

γ \in (0.8, 1)

and spin of a Kerr black hole up to

a ≃ 0.3

. Full article

(This article belongs to the Special Issue Relativistic Cosmology, Numerical Analysis, General Relativity and Modified Gravity Theories)

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