Talk abstract details

We investigate the nonlinear behaviour of the dynamical bar instability in three dimensional hydrodynamics in Newtonian gravitation. We find that the bar structure of the dynamical bar unstable stars cannot persist until the gravitational radiation reaction timescale, but it is destroyed in dynamical time scale. We show that the destruction is not caused by the linear momentum nor numerical viscosity, by checking the conservation of the linear momentum and that of the circulation along the closed curve. It is because of the nonlinearly exponential amplification of the odd azimuthal modes caused by the unstable system. The existence of all azimuthal modes is natural in an astrophysical scenario of the dynamical bar instability in newborn neutron stars, since fluctuation at the wavefront and/or asymmetry at the formation process should produce a small amplitude of all azimuthal modes. The gravitational waveform from the dynamical bar unstable stars is also computed and discussed, focusing on the duration period of the bar due to the nonlinearity of the system.