Type of Document	Dissertation
Author	Ou, Shangli
Author's Email Address	sou1@lsu.edu
URN	etd-10282004-114654
Title	Non-Linear Development of the Secular Bar-Mode Instability in Rapidly Rotating Neutron Stars
Degree	Doctor of Philosophy (Ph.D.)
Department	Physics & Astronomy
Advisory Committee	Advisor Name Title Joel E. Tohline Committee Chair Gabriela Gonzalez Committee Member Juhan Frank Committee Member Luis Lehner Committee Member Theda Daniels-Race Committee Member
Keywords	bar-mode instability gravitational radiation neutron stars
Date of Defense	2004-10-08
Availability	unrestricted
Abstract 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.
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