Article
Astronomy & Astrophysics
Bobir Toshmatov, Bobomurat Ahmedov
Summary: We investigate the tidal forces exerted by a spherically symmetric static parametrized black hole. Our analysis reveals that the radial and angular components of the tidal forces exerted by the black hole can exhibit both positive and negative values near the black hole, depending on matters of the spacetime parameters. Unlike the scenario with the Schwarzschild black hole, where the radial tidal force (angular tidal force) is always stretching (compressing) and becomes infinite at the center of the spacetime, the parametrized black hole allows for finite and compressing (stretching) forces within the event horizon. Additionally, we derive the geodesic deviation equations for a particle in free fall and proceed to solve them through numerical methods. Our analysis demonstrates that the spacetime parameters epsilon and a1 exhibit contrasting influences on the magnitudes of the physical quantities associated with tidal effects.
Article
Astronomy & Astrophysics
Alan Morales, Mauricio Bellini
Summary: This study investigates non-perturbative gravitational waves emitted from a collapsing system described by a scalar field, using an extended General Relativistic formalism with boundary terms included to avoid the final singularity.
PHYSICS OF THE DARK UNIVERSE
(2021)
Article
Physics, Multidisciplinary
Qanitah Ama-Tul-Mughani, Wardat Us Salam, Rabia Saleem
Summary: The study focuses on calculating analytic solutions for self-gravitating systems using the extended gravitational decoupling approach, transforming isotropic solutions to anisotropic domain, and checking stability and physical viability of the obtained solutions for compact stars. It is found that the models exhibit realistic behavior fulfilling physical constraints and stability criterion, suggesting the EGD technique is efficient for explaining interior structure of stellar objects.
EUROPEAN PHYSICAL JOURNAL PLUS
(2021)
Article
Astronomy & Astrophysics
F. Cipolletta, J. Kalinani, E. Giangrandi, B. Giacomazzo, R. Ciolfi, L. Sala, B. Giudici
Summary: This article introduces a new version of the GRMHD code Spritz, with an added neutrino leakage scheme and a series of tests to verify its correct implementation. It also discusses the implementation of high-order methods in the Spritz code.
CLASSICAL AND QUANTUM GRAVITY
(2021)
Article
Physics, Multidisciplinary
Ramiro Cayuso, Pau Figueras, Tiago Franca, Luis Lehner
Summary: The majority of extensions to general relativity encounter mathematical pathologies, but here we present an approach to deal with and extract physical consequences from these extensions.
PHYSICAL REVIEW LETTERS
(2023)
Article
Astronomy & Astrophysics
Artur Alho, Jose Natario, Paolo Pani, Guilherme Raposo
Summary: The study generalized Buchdahl's result by introducing the most general equation of state for elastic matter and computed the maximum compactness of self-gravitating objects in GR. It showed that elastic matter can exceed current theoretical limits but generally cannot reach the compactness of a black hole.
Article
Astronomy & Astrophysics
Jonas P. Pereira, Michal Bejger, Lucas Tonetto, German Lugones, Pawel Haensel, Julian Leszek Zdunik, Magdalena Sieniawska
Summary: Quark phases may have an impact on the dynamical stability of hybrid stars, increasing the stability window and causing relative radius differences, which could potentially provide a way to constrain the elasticity of quark phases.
ASTROPHYSICAL JOURNAL
(2021)
Article
Astronomy & Astrophysics
Shuichi Yokoyama
Summary: We investigate the gravitational collapse of a thick shell of fluid in an isotropic homogeneous universe without radiation. By constructing interpolated solutions, we determine the orbit of the fluid shell and confirm that the total energy remains independent of the given time evolution.
Article
Astronomy & Astrophysics
Ryota Katsube, Wai-Hong Tam, Masahiro Hotta, Yasusada Nambu
Summary: This study discusses the conceptual issues of using test particle geodesics in curved spacetimes for DL metric detectors, emphasizing the advantages of DL metric detectors from the perspective of general coordinate transformations. It explores the fundamental question of DL isometry and suggests that postmeasurement states in superposed spacetimes may remain in the same superposition even after being observed by DL metric detectors. Additionally, metric-detection DL methods are demonstrated in 1-dimensional AdS spacetimes to estimate cosmological constants and charges, suggesting a correspondence with quantum measurement devices in conformal field theory.
Article
Physics, Particles & Fields
Lavinia Heisenberg, Manuel Hohmann, Simon Kuhn
Summary: We derive the most general homogeneous and isotropic teleparallel geometries, defined by a metric and a flat, affine connection. We find that there are five branches of connection solutions, which are connected via several limits, and can further be restricted to the torsion-free and metric-compatible cases. We apply our results to several classes of general teleparallel gravity theories and derive their cosmological dynamics for all five branches. Our results show that for large subclasses of these theories the dynamics reduce to that of closely related metric or symmetric teleparallel gravity theories, while for other subclasses up to two new scalar degrees of freedom participate in the cosmological dynamics.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Astronomy & Astrophysics
Thomas Madler, Emanuel Gallo
Summary: Using a quasispherical approximation and affine-null coordinates, this paper presents high order approximations of the metric functions for a slowly rotating stationary and axisymmetric vacuum spacetime. It verifies the equivalence of the metric with the Kerr metric in the slowly rotating approximation and shows that the additional integration constants can be absorbed into the overall Komar mass and Komar angular momentum of a slowly rotating black hole.
Article
Physics, Fluids & Plasmas
A. Souto-Iglesias, J. Bonet Avalos, M. Antuono, A. Colagrossi
Summary: In this study, the SPH method is used to model micropolar fluids and focus on their dissipation mechanisms. A dissipation function is defined at the particle level, dependent on relative velocity and an additional spin degree of freedom. The model is enriched with spin derivatives for maximal generality as an isotropic model. Numerical verification and validation tests show that SPH accurately models this type of dynamics.
Article
Astronomy & Astrophysics
Leandro G. Althaus, Alejandro H. Corsico, Maria E. Camisassa, Santiago Torres, Pilar Gil-Pons, Alberto Rebassa-Mansergas, Roberto Raddi
Summary: We used the lpcode to calculate evolutionary sequences for ultra-massive white dwarfs, taking into account the effects of general relativity. We found that carbon-oxygen white dwarfs more massive than 1.382 M☉ become gravitationally unstable due to general relativity effects. The properties of these white dwarfs, including their radius and evolutionary behavior, are strongly affected by general relativity. Additionally, we explored the pulsational properties of relativistic ultra-massive white dwarfs for the first time and found significant differences in period spacings and oscillation kinetic energies.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Physics, Particles & Fields
J. Andrade, D. Santana
Summary: In this work, a new interior isotropic extension of Einstein's universe solution is constructed using the gravitational decoupling framework and the extended minimal geometric deformation. The resulting model satisfies the fundamental physical acceptance conditions. Additionally, the energy exchange between the Einstein's fluid distribution and an extra perfect fluid supporting the resulting isotropic stellar configuration is studied.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Astronomy & Astrophysics
Taichiro Kugo, Ryuichi Nakayama, Nobuyoshi Ohta
Summary: Unimodular gravity (UG) is an important theory that may explain the smallness of the cosmological constant. By developing novel methods of gauge fixing and studying theories derived from Fourier transform of general relativity, we aim to understand the covariant quantization of UG and clarify differences from GR.