Gravitational Radiation from Rapidly Rotating Non-axisymmetric Stellar Cores

Markus Rampp, Maximilian Ruffert and Ewald Müller

Among potential sources which emit gravitational waves core collapse supernovae are thought to be one of the most promising to be detected on earth by gravitational wave detectors. It is commonly thought that the gravitational wave signal is particularly strong, if the core becomes non-axisymmetric due to secular and/or dynamical instabilities caused by its fast rotation.

For this reason we have performed three-dimensional Newtonian hydrodynamic simulations of collapsing rotating stellar cores, which are secularly and/or dynamically unstable against tri-axial deformations. The initial models are taken from the comprehensive parameter study of collapsing rotating polytropes performed by T. Zwerger and E. Müller (A&A 320 (1997), 209).

Compared with the axisymmetric simulations, no significant changes of the dynamics and the gravitational wave signal on time scales of several 10 ms were found for the secularly unstable models. Starting from the only dynamically unstable model (see picture above) we calculated two models with different initial perturbations (MD1, MD2) and one second-collapse-model (MD3). Both random and coherent large scale initial perturbations eventually give rise to a dominant bar-like deformation of the inner (unshocked) core. In spite of the pronounced tri-axial deformation of certain parts of the core no considerable enhancement of the gravitational radiation is found. This is due to the fact that rapidly rotating cores re-expand after core bounce on a dynamical time scale before non-axisymmetric instabilities enter the nonlinear regime. Hence, when the core becomes tri-axial, it is no longer very compact. We find that it is rather unlikely to expect gravitational wave signals from dynamic non-axisymmetric instabilities with sufficient strength and rate (i.e. several per year) to be observable with the large interferometric gravitational wave antennas presently under construction.

A detailed description of the results can be found in a preprint MPA 1054 entitled "Simulations of non-axisymmetric rotational core collapse", by M. Rampp, E. Müller, M. Ruffert, published in A&A, 332 (1998), 969.

Movies (in MPEG format) and compilations of selected snapshots (JPG) showing the dynamical evolution of the three 3D-simulations can be clicked below. In the ray-cast (3D) pictures the colour-intensity encodes the mass-density and the colours the temperature (increasing from red, yellow, green to blue). The slices in the equatorial plane (2D) display the mass-density distribution as false colour plots.