Accurate evolutions of inspiralling neutronstar binaries: Prompt and delayed collapse to a black hole
Abstract
Binary neutronstar systems represent primary sources for the gravitationalwave detectors that are presently operating or are close to being operating at the target sensitivities. We present a systematic investigation in full general relativity of the dynamics and gravitationalwave emission from binary neutron stars which inspiral and merge, producing a black hole surrounded by a torus. Our results represent the state of the art from several points of view: (i) We use highresolution shockcapturing methods for the solution of the hydrodynamics equations and highorder finitedifferencing techniques for the solution of the Einstein equations; (ii) We employ adaptive meshrefinement techniques with “moving boxes” that provide highresolution around the orbiting stars; (iii) We use as initial data accurate solutions of the Einstein equations for a system of binary neutron stars in irrotational quasicircular orbits; (iv) We exploit the isolatedhorizon formalism to measure the properties of the black holes produced in the merger; (v) Finally, we use two approaches, based either on gaugeinvariant perturbations or on Weyl scalars, to calculate the gravitational waves emitted by the system. Within our idealized treatment of the matter, these techniques allow us to perform accurate evolutions on time scales never reported before (i.e. ̃30ms) and to provide the first complete description of the inspiral and merger of a neutronstar binary leading to the prompt or delayed formation of a black hole and to its ringdown. We consider either a polytropic equation of state or that of an ideal fluid and show that already with this idealized treatment a very interesting phenomenology can be described. In particular, we show that while highermass polytropic binaries lead to the prompt formation of a rapidly rotating black hole surrounded by a dense torus, lowermass binaries give rise to a differentially rotating star, which undergoes large oscillations and emits large amounts of gravitational radiation. Eventually, also the hypermassive neutron star collapses to a rotating black hole surrounded by a torus. Finally, we also show that the use of a nonisentropic equation of state leads to significantly different evolutions, giving rise to a delayed collapse also with highmass binaries, as well as to a more intense emission of gravitational waves and to a geometrically thicker torus.
 Publication:

Physical Review D
 Pub Date:
 October 2008
 DOI:
 10.1103/PhysRevD.78.084033
 arXiv:
 arXiv:0804.0594
 Bibcode:
 2008PhRvD..78h4033B
 Keywords:

 04.30.Db;
 04.40.Dg;
 95.30.Lz;
 97.60.Jd;
 Wave generation and sources;
 Relativistic stars: structure stability and oscillations;
 Hydrodynamics;
 Neutron stars;
 General Relativity and Quantum Cosmology;
 Astrophysics
 EPrint:
 35 pages, 29 figures, corrected few typos to match the published version. Highresolution figures and animations can be found at http://numrel.aei.mpg.de/Visualisations/Archive/BinaryNeutronStars/Relativistic_Meudon/index.html