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One of the most common assumptions in the study of neutron star models and their oscillations is that the pressure is isotopic, however there are arguments that this may not be correct. Thus in the present paper we make a first step towards…

General Relativity and Quantum Cosmology · Physics 2012-06-25 Daniela D. Doneva , Stoytcho S. Yazadjiev

In this work, we consider polar perturbations and we calculate the frequency and damping time of the quadrupolar fundamental f -mode of compact objects, constructed using a wide range of model-independent hybrid equations of state that…

High Energy Astrophysical Phenomena · Physics 2023-06-29 Ignacio F. Ranea-Sandoval , Mauro Mariani , Marcos O. Celi , M. Camila Rodríguez , Lucas Tonetto

In the modern era of abundant X-ray detections and the increasing momentum of gravitational waves astronomy, tests of General Relativity in strong field regime become increasingly feasible and their importance for probing gravity cannot be…

General Relativity and Quantum Cosmology · Physics 2020-09-25 Victor I. Danchev , Daniela D. Doneva , Stoytcho S. Yazadjiev

The thermodynamic relation between pressure and density (i.e. the equation of state) of cold supranuclear matter is critical in describing neutron stars, yet it remains one of the largest uncertainties in nuclear physics. The extraction of…

General Relativity and Quantum Cosmology · Physics 2022-03-11 Zack Carson , Katerina Chatziioannou , Carl-Johan Haster , Kent Yagi , Nicolás Yunes

In this work, we investigate hot, isentropic compact stars in the limiting cases of static and maximally rotating configurations, focusing on how variations in the symmetry energy of the equation of state derived from covariant density…

High Energy Astrophysical Phenomena · Physics 2026-02-02 Stefanos Tsiopelas , Armen Sedrakian , Micaela Oertel

Some models (such as the Skyrme model, a low-energy effective field theory for QCD) suggest that the high-density matter prevailing in neutron star interiors may be significantly anisotropic. Anisotropy is known to affect the bulk…

General Relativity and Quantum Cosmology · Physics 2015-06-05 Hector O. Silva , Caio F. B. Macedo , Emanuele Berti , Luís C. B. Crispino

Unitarity of evolution in gravitational collapses implies existence of macroscopic stable horizonless objects. With such objects in mind, we study the effects of anisotropy of pressures on the stability of stars. We consider stars in four…

High Energy Physics - Theory · Physics 2015-10-05 S. Kalyana Rama

We investigate the possible sequels, for the hybrid compact stars consisting of nucleons, hyperons and three flavour color-flavor-locked quarks phase under global neutrality and chemical equilibrium conditions. The hadron equations of state…

Nuclear Theory · Physics 2019-09-18 Suman Thakur , Shashi K Dhiman

We provide a summary of several parametrisations for the nuclear equation of state that have been proposed over the past decades and list viable ranges for their parameters. Based on these parametrisations, we construct a large database of…

General Relativity and Quantum Cosmology · Physics 2025-11-27 Christian J. Krüger , Mariachiara Celato

We investigate nonradial $f$-mode oscillations of hybrid neutron stars in full general relativity, employing hybrid equations of state describing a nuclear outer core and a pasta-phase transition to a quark-matter core. The validity of…

General Relativity and Quantum Cosmology · Physics 2024-11-26 Zi-Yue Zheng , Jin-Biao Wei , Huan Chen , Xiao-Ping Zheng , G. F. Burgio , H. -J. Schulze

We investigate the impact of strange matter equations of state involving $\Lambda$ hyperons, Bose-Einstein condensate of $K^-$ mesons and first order hadron-quark phase transition on moment of inertia, quadrupole moment and tidal…

High Energy Astrophysical Phenomena · Physics 2018-04-04 D. Bandyopadhyay , S. A. Bhat , P. Char , D. Chatterjee

The presence of Dark matter (DM) within a neutron star (NS) can substantially influence the macroscopic properties. It is commonly assumed that the pressure inside an NS is isotropic, but in reality, pressure is locally anisotropic. This…

Cosmology and Nongalactic Astrophysics · Physics 2025-12-12 Premachand Mahapatra , Chiranjeeb Singha , Ayush Hazarika , Prasanta Kumar Das

Spherically symmetric relativistic stars with the polytropic equation of state, which possess the local pressure anisotropy, are considered in the context of general relativity. The modified Lane-Emden equations are derived for the special…

General Relativity and Quantum Cosmology · Physics 2018-01-25 A. A. Isayev

We study how rapid rotation influences the relation between the normalized moment of inertia $\bar{I}$ and quadrupole moment $\bar{Q}$ for scalarized neutron stars. The questions one has to answer are whether the EOS universality is…

General Relativity and Quantum Cosmology · Physics 2015-06-22 Daniela D. Doneva , Stoytcho S. Yazadjiev , Kalin V. Staykov , Kostas D. Kokkotas

In an earlier treatment it was demonstrated that general relativity gives higher values of surface tension in strange stars with quark matter than neutron stars.We generate the modified Tolman-Oppenheimer-Volkoff equation to incorporate…

General Relativity and Quantum Cosmology · Physics 2009-11-13 R. Sharma , S. D. Maharaj

We investigate systematically the quark-hadron mixed phase in dense stellar matter, and its influence on compact star structures. The properties of quark matter and hadronic matter are fixed based on various model predictions. Beside…

High Energy Physics - Phenomenology · Physics 2020-07-29 Cheng-Jun Xia , Toshiki Maruyama , Nobutoshi Yasutake , Toshitaka Tatsumi , Hong Shen , Hajime Togashi

We show that the inclusion of simple anisotropic pressures stops the isotropic Friedmann universe being a stable attractor as an initial or final singularity is approached when pressures can exceed the energy density. This shows that the…

General Relativity and Quantum Cosmology · Physics 2014-11-20 John D Barrow , Kei Yamamoto

Compact objects have an intrinsic anisotropy due to the presence of strong magnetic fields that cause considerable modifications on the equations of state (EoS). In this work, we study the impact of this anisotropy in the size and shape of…

General Relativity and Quantum Cosmology · Physics 2020-02-05 S. López Pérez , D. Manreza Paret , G. Quintero Angulo , A. Pérez Martínez , D. Alvear Terrero

We systematically investigate the fundamental oscillation frequencies of dark matter admixed neutron stars, focusing on models with self-interacting fermionic dark matter that couples to normal matter solely through gravity. The analysis is…

High Energy Astrophysical Phenomena · Physics 2026-02-24 Hajime Sotani , Ankit Kumar

A polytropic quark star model is suggested in order to establish a general framework in which theoretical quark star models could be tested by observations. The key difference between polytropic quark stars and the polytropic model studied…

Astrophysics · Physics 2009-06-23 X. Y. Lai , R. X. Xu