Merger-inspired rotation laws and the low-T/W instability in neutron stars

Abstract

Implementing a family of differential rotation laws inspired by binary neutron-star merger remnants, we consider the impact of the rotation profile on the low-T/W instability. We use time evolutions of the linearised dynamical equations, in Newtonian gravity, to study non-axisymmetric oscillations and identify the unstable modes. The presence and evolution of the low-T/W instability is monitored with the canonical energy and angular momentum, while the growth time is extracted from the evolved kinetic energy. The results for the new rotation laws highlight similarities with the commonly considered j-constant law. The instability sets in when an oscillation mode co-rotates with the star (i.e. whenever there is a point where the mode's pattern speed matches the bulk angular velocity) and grows faster deep inside the co-rotation region. However, the new profiles add features, like an additional co-rotation point to the problem, which affect the onset of instability. The rotation laws influence more drastically the oscillation frequencies of the l=m=2 f-mode in fast rotating models, but affect the instability growth time at any rotation rate. We also identify models where the low-T/W instability appears to be triggered by inertial modes. We discuss to what extent the inferred qualitative behaviour is likely to be of observational relevance.

12 pages, 8 figures and 4 tables. Version accepted for publication in MNRAS

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Cited by in corpus (11)

• Analytic models of the spectral properties of gravitational waves from neutron star merger remnants
• Insights into non-axisymmetric instabilities in three-dimensional rotating supernova models with neutrino and gravitational-wave signatures
• Axisymmetric models for neutron star merger remnants with realistic thermal and rotational profiles
• Equilibrium sequences of differentially rotating stars with post-merger-like rotational profiles
• Models of binary neutron star remnants with tabulated equations of state
• Decihertz gravitational waves from double white dwarf merger remnants
• Equilibriums of extremely magnetized compact stars with force-free magnetotunnels
• Exploring the Potential for Detecting Rotational Instabilities in Binary Neutron Star Merger Remnants with Gravitational Wave Detectors
• A gravitational-wave perspective on neutron-star seismology
• Quasi-stationary sequences of hyper massive neutron stars with exotic equations of state
• Convective stability analysis of massive neutron stars formed in binary mergers