Instabilities in neutron-star postmerger remnants

Abstract

Using nonlinear, fully relativistic, simulations we investigate the dynamics and gravitational-wave signature associated with instabilities in neutron star postmerger remnants. For simplified models of the remnant we establish the presence of an instability in stars with moderate $T/|W|$, the ratio between the kinetic and the gravitational potential energies. Detailed analysis of the density oscillation pattern reveals a \emph{local} instability in the inner region of the more realistic differential rotation profile. We apply Rayleigh's inflection theorem and Fjørtoft's theorem to analyze the stability criteria concluding that this \emph{inner local} instability originates from a shear instability close to the peak of the angular velocity profile, and that it later evolves into a fast-rotating m=2 oscillation pattern. We discuss the importance of the presence of a corotation point in the fluid, its connection with the shear instability, and comparisons to the Rossby wave and Papaloizou Pringle instabilities considered in the wider literature.

17 Figures. Accepted for publication in Phys. Rev. D

References in corpus (12)

• Gravitational-wave sensitivity curves
• Testing Approximations of Thermal Effects in Neutron Star Merger Simulations
• Properties of hypermassive neutron stars formed in mergers of spinning binaries
• Gravitational waves and mass ejecta from binary neutron star mergers: Effect of the mass-ratio
• Accurate simulations of the dynamical bar-mode instability in full General Relativity
• Extraction of Gravitational Waves in Numerical Relativity
• First 100 ms of a long-lived magnetized neutron star formed in a binary neutron star merger
• Gravitational waves and mass ejecta from binary neutron star mergers: Effect of the stars' rotation
• Unexpected Dynamical Instabilities In Differentially Rotating Neutron Stars
• Rossby Wave Instability in three dimensional discs
• Equation of state effects and one-arm spiral instability in hypermassive neutron stars formed in eccentric neutron star mergers
• Modeling differential rotations of compact stars in equilibriums