Gravitational waves from axisymmetric rotating stellar core collapse to a neutron star in full general relativity

Abstract

Axisymmetric numerical simulations of rotating stellar core collapse to a neutron star are performed in the framework of full general relativity. The so-called Cartoon method, in which the Einstein field equations are solved in the Cartesian coordinates and the axisymmetric condition is imposed around the $y=0$ plane, is adopted. The hydrodynamic equations are solved in the cylindrical coordinates (on the $y=0$ plane in the Cartesian coordinates) using a high-resolution shock-capturing scheme with the maximum grid size $(2500,2500)$. A parametric equation of state is adopted to model collapsing stellar cores and neutron stars following Dimmelmeier et al. It is found that the evolution of central density during the collapse, bounce, and formation of protoneutron stars agree well with those in the work of Dimmelmeier et al. in which an approximate general relativistic formulation is adopted. This indicates that such approximation is appropriate for following axisymmetric stellar core collapses and subsequent formation of protoneutron stars. Gravitational waves are computed using a quadrupole formula. It is found that the waveforms are qualitatively in good agreement with those by Dimmelmeier et al. However, quantitatively, two waveforms do not agree well. Possible reasons for the disagreement are discussed.