Non-Linear Development of the Secular Bar-Mode Instability in Rapidly Rotating Neutron Stars

• Main Author: Ou, Shangli
• Other Authors: Theda Daniels-Race
• Format: Others
• Language: en
• Published: LSU 2004
• Subjects: Physics & Astronomy
• Online Access: http://etd.lsu.edu/docs/available/etd-10282004-114654/

We present results from investigations of the nonlinear development of the secular bar-mode instability that is driven by gravitational radiation-reaction (GRR) forces in rotating neutron stars. Our fully three-dimensional hydrodynamical simulations have shown that, in the absence of any competing viscous effects, initially uniformly rotating axisymmetric n=1/2 polytropic stars with a ratio of rotational to gravitational potential energy greater than the critical limit are driven by GRR forces to a bar-like structure, as predicted by linear theory. The pattern frequency of the bar slows to nearly zero, that is, the bar becomes almost stationary as viewed from an inertial frame of reference as GRR forces remove energy and angular momentum from the star. In this "Dedekind-like" state, rotational energy is stored as motion of the fluid in highly noncircular orbits inside the bar. However, in a very short time after its formation, the bar loses its initially coherent structure as the ordered flow inside the bar is disrupted by what appears to be a purely hydrodynamical, short-wavelength, "shearing" type instability. The gravitational waveforms generated by such an event are determined, and an estimate of the detectability of these waves is presented. Our results also suggest that since a Dedekind-like configuration is susceptible to this turbulent instability, the long believed evolutionary path of a secularly unstable star driven by gravitational radiation toward the Dedekind ellipsoid, becomes questionable.