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We study models of uniformly and differentially rotating neutron stars in the framework of post-Newtonian approximation in general relativity as established by Chandrasechar. In particular, we adopt the polytropic equation of state in order…

High Energy Astrophysical Phenomena · Physics 2023-05-05 Athanasios Fotopoulos , Vasileios G. Karageorgopoulos , Vassilis S. Geroyannis

We propose a new numerical method to compute quasi-equilibrium sequences of general relativistic irrotational binary neutron star systems. It is a good approximation to assume that (1) the binary star system is irrotational, i.e. the…

General Relativity and Quantum Cosmology · Physics 2009-10-31 Koji Uryu , Yoshiharu Eriguchi

We have developed a new numerical scheme to obtain quasiequilibrium structures of nonaxisymmetric compact stars such as binary neutron star systems as well as the spacetime around those systems in general relativity. Concerning…

General Relativity and Quantum Cosmology · Physics 2009-10-31 Fumihiko Usui , Koji Uryu , Yoshiharu Eriguchi

We report on general relativistic calculations of quasiequilibrium configurations of binary neutron stars in circular orbits with zero vorticity. These configurations are expected to represent realistic situations as opposed to corotating…

General Relativity and Quantum Cosmology · Physics 2009-10-31 S. Bonazzola , E. Gourgoulhon , J. -A. Marck

A solution to an equilibrium of irrotational binary polytropic stars in Newtonian gravity is expanded in a power of \epsilon=a_0/R, where R and a_0 are the separation of the binary system and the radius of each star for R=\infty. For the…

Astrophysics · Physics 2009-10-31 Keisuke Taniguchi , Takashi Nakamura

Triaxial neutron stars can be sources of continuous gravitational radiation detectable by ground-based interferometers. The amplitude of the emitted gravitational wave can be greatly affected by the state of the hydrodynamical fluid flow…

General Relativity and Quantum Cosmology · Physics 2024-04-24 Yufeng Luo , Antonios Tsokaros , Roland Haas , Koji Uryu

The equilibrium configurations of slowly rotating anisotropic self-gravitating fluids are computed using the extended Hartle structure equations, including anisotropic effects, derived in our previous paper. We focus on the so-called…

General Relativity and Quantum Cosmology · Physics 2025-10-20 Philip Beltracchi , Camilo Posada

Quasi-local variables, i.e. quantities whose values can be derived from physics accessible within an arbitrarily small neighborhood of a spacetime point, are used to construct the equation of state (EoS) for the anisotropic fluid in the…

General Relativity and Quantum Cosmology · Physics 2011-01-20 Dubravko Horvat , Sasa Ilijic , Anja Marunovic

Equilibria of binary neutron stars in close circular orbits are computed numerically in a waveless formulation: The full Einstein-relativistic-Euler system is solved on an initial hypersurface to obtain an asymptotically flat form of the…

General Relativity and Quantum Cosmology · Physics 2009-11-11 Koji Uryu , Francois Limousin , John L. Friedman , Eric Gourgoulhon , Masaru Shibata

In this paper we present a new approach to the inverse problem for relativistic stars using quasinormal modes and the piecewise polytropic parametrization of the equation of state. The algorithm is a piecewise polytropic meshing and…

General Relativity and Quantum Cosmology · Physics 2019-05-10 Juan Mena-Fernández , Luis Manuel González-Romero

We construct analytic models of incompressible, rigidly rotating stars in PN gravity and study their stability against nonaxisymmetric Jacobi-like bar modes. PN configurations are modeled by homogeneous triaxial ellipsoids and the metric is…

General Relativity and Quantum Cosmology · Physics 2009-10-30 S. L. Shapiro , S. Zane

We present results of numerical computations of quasiequilibrium sequences of binary neutron stars with zero vorticity, in the general relativistic framework. The Einstein equations are solved under the assumption of a conformally flat…

General Relativity and Quantum Cosmology · Physics 2007-05-23 S. Bonazzola , E. Gourgoulhon , J. -A. Marck

Stationary and axisymmetric solutions of relativistic rotating stars with strong mixed poloidal and toroidal magnetic fields are obtained numerically. Because of the mixed components of the magnetic field, the underlying stationary and…

High Energy Astrophysical Phenomena · Physics 2014-11-13 Koji Uryu , Eric Gourgoulhon , Charalampos Markakis , Kotaro Fujisawa , Antonios Tsokaros , Yoshiharu Eriguchi

We construct new models of black hole-neutron star binaries in quasiequilibrium circular orbits by solving Einstein's constraint equations in the conformal thin-sandwich decomposition together with the relativistic equations of…

General Relativity and Quantum Cosmology · Physics 2008-11-26 Keisuke Taniguchi , Thomas W. Baumgarte , Joshua A. Faber , Stuart L. Shapiro

We study equilibrium sequences of close binary systems composed of identical polytropic stars in Newtonian gravity. The solving method is a multi-domain spectral method which we have recently developed. An improvement is introduced here for…

General Relativity and Quantum Cosmology · Physics 2009-11-07 Keisuke Taniguchi , Eric Gourgoulhon , Silvano Bonazzola

We perform fully relativistic calculations of binary neutron stars in quasi-equilibrium circular orbits. We integrate Einstein's equations together with the relativistic equation of hydrostatic equilibrium to solve the initial value problem…

General Relativity and Quantum Cosmology · Physics 2009-10-30 T. W. Baumgarte , G. B. Cook , M. A. Scheel , S. L. Shapiro , S. A. Teukolsky

Viscosity driven bar mode secular instabilities of rapidly rotating neutron stars are studied using LORENE/Nrotstar code. These instabilities set a more rigorous limit to the rotation frequency of neutron star than the Kepler frequency/mass…

High Energy Astrophysical Phenomena · Physics 2018-04-30 Arkadip Basak

Outcomes of numerical relativity simulations of massive core collapses or binary neutron star mergers with moderate masses suggest formations of rapidly and differentially rotating neutron stars. Subsequent fall back accretion may also…

High Energy Astrophysical Phenomena · Physics 2017-11-29 Koji Uryu , Antonios Tsokaros , Luca Baiotti , Filippo Galeazzi , Keisuke Taniguchi , Shin'ichirou Yoshida

Two new families of self-consistent axisymmetric truncated equilibrium models for the description of quasi-relaxed rotating stellar systems are presented. The first extends the spherical King models to the case of solid-body rotation. The…

Astrophysics of Galaxies · Physics 2015-06-03 A. L. Varri , G. Bertin

We report work towards a relativistic formulation for modeling strongly magnetized neutron stars, rotating or in a close circular orbit around another neutron star or black hole, under the approximations of helical symmetry and ideal MHD.…

General Relativity and Quantum Cosmology · Physics 2011-11-08 Charalampos Markakis , Koji Uryu , Eric Gourgoulhon