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A novel equation of state used for analysis of the heavy ion collision experimental data is generalized to also describe the matter inside neutron stars. This approach differs from others by including an induced surface tension caused by…

High Energy Astrophysical Phenomena · Physics 2019-02-20 V. Sagun , I. Lopes , A. Ivanytskyi

Medvedev & Narayan have described a hot accretion flow onto a spinning neutron star in which the gas viscously brakes the spin of the star. Their self-similar solution has the surprising property that the density, temperature and angular…

Astrophysics · Physics 2009-11-07 Ramesh Narayan , Mikhail V. Medvedev

We present a numerical scheme that solves the initial value problem in full general relativity for a binary neutron star in quasi-equilibrium. While Newtonian gravity allows for a strict equilibrium, a relativistic binary system emits…

General Relativity and Quantum Cosmology · Physics 2007-05-23 Thomas W. Baumgarte , Stuart L. Shapiro , Gregory B. Cook , Mark A. Scheel , Saul A. Teukolsky

This paper presents a novel shooting method for solving two-point boundary value problems for second order ordinary differential equations. The method works as follows: first, a guess for the initial condition is made and an integration of…

Numerical Analysis · Mathematics 2017-02-08 Stefan M. Filipov , Ivan D. Gospodinov , Istvan Farago

The early post-merger phase of a binary neutron-star coalescence is shaped by characteristic rotational velocities as well as violent density oscillations and offers the possibility to constrain the properties of neutron star matter by…

General Relativity and Quantum Cosmology · Physics 2025-03-10 Michail Chabanov , Luciano Rezzolla

We model two mergers of orbiting binary neutron stars, the first forming a black hole and the second a differentially rotating neutron star. We extract gravitational waveforms in the wave zone. Comparisons to a post-Newtonian analysis allow…

General Relativity and Quantum Cosmology · Physics 2008-11-26 Matthew Anderson , Eric W. Hirschmann , Luis Lehner , Steven L. Liebling , Patrick M. Motl , David Neilsen , Carlos Palenzuela , Joel E. Tohline

A new approach to construct initial data for binary systems with neutron star components is introduced. The approach is a generalization of the puncture initial data method for binary black holes based on Bowen-York solutions to the…

General Relativity and Quantum Cosmology · Physics 2016-09-28 Michael Clark , Pablo Laguna

A method is described to solve the Poisson problem for a three dimensional source distribution that is periodic into one direction. Perpendicular to the direction of periodicity a free space (or open) boundary is realized. In beam physics,…

Accelerator Physics · Physics 2016-03-23 M. Dohlus , Ch. Henning

We consider hot accretion onto a rapidly spinning neutron star (or any other compact object with a surface). A radiative hot settling flow has been discovered at low accretion rates in the early work by Medvedev & Narayan (2001) and…

Astrophysics · Physics 2009-11-10 Mikhail V. Medvedev

This work is motivated by the frequent occurrence of boundary value problems with various boundary conditions in the modeling of some problems in engineering and physical science. Here we propose a new technique to force the positive…

Numerical Analysis · Mathematics 2019-06-19 Babak Azarnavid , Mohammad Nabati , Mahdi Emamjome , Kourosh Parand

A general relativistic version of the Euler equation for perfect fluid hydrodynamics is applied to a system of two neutron stars orbiting each other. In the quasi-equilibrium phase of the evolution of this system, a first integral of motion…

General Relativity and Quantum Cosmology · Physics 2009-10-30 S. Bonazzola , E. Gourgoulhon , J. -A. Marck

The upper bound of the speed of sound in dense nuclear matter is one of the most interesting but still unsolved problems in Nuclear Physics. Theoretical studies in connection with recent observational data of isolated neutron stars as well…

Nuclear Theory · Physics 2021-01-27 A. Kanakis-Pegios , P. S. Koliogiannis , Ch. C. Moustakidis

We present a new high-order accurate spectral element solution to the two-dimensional scalar Poisson equation subject to a general Robin boundary condition. The solution is based on a simplified version of the shifted boundary method…

Numerical Analysis · Mathematics 2023-10-27 Jens Visbech , Allan Peter Engsig-Karup , Mario Ricchiuto

This paper is concerned with the initial-boundary value problem on the full Euler-Poisson system for ions over a half line. We establish the existence of stationary solutions under the Bohm criterion similar to the isentropic case and…

Analysis of PDEs · Mathematics 2020-11-05 Renjun Duan , Haiyan Yin , Changjiang Zhu

Binary boson stars can be used to model the nonlinear dynamics and gravitational wave signals of merging ultracompact, but horizonless, objects. However, doing so requires initial data satisfying the Hamiltonian and momentum constraints of…

General Relativity and Quantum Cosmology · Physics 2023-12-05 Nils Siemonsen , William E. East

We present a simple modification of the direct-forcing immersed boundary method (IBM) proposed by Uhlmann [J. Comput. Phys, 2005] in order to enable it to be applied to particulate flows with solid-to-fluid density ratios around unity. The…

Fluid Dynamics · Physics 2023-06-21 Manuel Garcia-Villalba , Blanca Fuentes , Jan Dusek , Manuel Moriche , Markus Uhlmann

In this paper, we discuss an initial boundary value problem for the stochastic wave equation involving the nonlinear damping term $|u_t|^{q-2}u_t$ and a source term of the type $|u|^{p-2}u$. We firstly establish the local existence and…

Analysis of PDEs · Mathematics 2011-04-26 Hongjun Gao , Boling Guo , Fei Liang

We consider the hydrodynamics of the outer core of a neutron star under conditions when both neutrons and protons are superfluid. Starting from the equation of motion for the phases of the wave functions of the condensates of neutron pairs…

Quantum Gases · Physics 2017-03-02 D. N. Kobyakov , C. J. Pethick

We present an efficient and accurate algorithm for solving the Poisson equation in spherical polar coordinates with a logarithmic radial grid and open boundary conditions. The method employs a divide-and-conquer strategy, decomposing the…

Instrumentation and Methods for Astrophysics · Physics 2025-07-10 Jeonghyeon Ahn , Woong-Tae Kim , Yonghwi Kim

For the problems indicated in the title, a further development of a new approach (different from those applied before) is given. A basic problem under consideration arises in viscous incompressible fluid dynamics and describes self-similar…

Analysis of PDEs · Mathematics 2018-04-18 Nadezhda Konyukhova , Sergey Kurochkin , Mikhail Soloviev