Three-dimensional general-relativistic hydrodynamic simulations of binary neutron star coalescence and stellar collapse with multipatch grids
We present a new three-dimensional, general-relativistic hydrodynamic evolution scheme coupled to dynamical spacetime evolutions which is capable of efficiently simulating stellar collapse, isolated neutron stars, black hole formation, and binary neutron star coalescence. We make use of a set of adapted curvilinear grids (multipatches) coupled with flux-conservative, cell-centered adaptive mesh refinement. This allows us to significantly enlarge our computational domains while still maintaining high resolution in the gravitational wave extraction zone, the exterior layers of a star, or the region of mass ejection in merging neutron stars. The fluid is evolved with a high-resolution, shock-capturing finite volume scheme, while the spacetime geometry is evolved using fourth-order finite differences. We employ a multirate Runge-Kutta time-integration scheme for efficiency, evolving the fluid with second-order integration and the spacetime geometry with fourth-order integration. We validate our code by a number of benchmark problems: a rotating stellar collapse model, an excited neutron star, neutron star collapse to a black hole, and binary neutron star coalescence. The test problems, especially the latter, greatly benefit from higher resolution in the gravitational wave extraction zone, causally disconnected outer boundaries, and application of Cauchy-characteristic gravitational wave extraction. We show that we are able to extract convergent gravitational wave modes up to (ℓ,m)=(6,6). This study paves the way for more realistic and detailed studies of compact objects and stellar collapse in full three dimensions and in large computational domains. The multipatch infrastructure and the improvements to mesh refinement and hydrodynamics codes discussed in this paper will be made available as part of the open-source Einstein Toolkit.
Additional Information© 2013 American Physical Society. (Received 7 December 2012; published 18 March 2013) We acknowledge helpful discussions with Peter Diener, Frank Löffler, Uschi C. T. Gamma, and members of our Simulating eXtreme Spacetimes (SXS) Collaboration (http://www.black-holes.org). This research is partially supported by NSF Grants No. AST-0855535, No. AST-1212170, No. PHY-1212460, No. PHY-1151197, and No. OCI-0905046, by the Alfred P. Sloan Foundation, and by the Sherman Fairchild Foundation. C. R. acknowledges support by NASA through Einstein Postdoctoral Fellowship Grant No. PF2-130099 awarded by the Chandra X-ray center, which is operated by the Smithsonian Astrophysical Observatory for NASA under Contract No. NAS8-03060. R. H. acknowledges support by the Natural Sciences and Engineering Council of Canada. The simulations were performed on the Caltech compute cluster Zwicky (NSF MRI Grant No. PHY-0960291), on supercomputers of the NSF XSEDE network under computer time allocation TG-PHY100033, on machines of the Louisiana Optical Network Initiative under grant loni_numrel07, and at the National Energy Research Scientific Computing Center (NERSC), which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. All figures were generated with the Python-based matplotlib package (http://matplotlib.org/). C. R. is an Einstein Fellow, and C. D. O. is an Alfred P. Sloan Research Fellow.
Published - PhysRevD.87.064023.pdf
Submitted - 1212.1191.pdf