Equation of state effects and one-arm spiral instability in hypermassive neutron stars formed in eccentric neutron star mergers

Abstract

We continue our investigations of the development and importance of the one-arm spiral instability in long-lived hypermassive neutron stars (HMNSs) formed in dynamical capture binary neutron star mergers. Employing hydrodynamic simulations in full general relativity, we find that the one-arm instability is generic in that it can develop in HMNSs within a few tens of milliseconds after merger for all equations of state in our survey. We find that mergers with stiffer equations of state tend to produce HMNSs with stronger $m=2$ azimuthal mode density deformations, and weaker $m=1$ components, relative to softer equations of state. We also find that for equations of state that can give rise to double-core HMNSs, large $m=1$ density modes can already be present due to asymmetries in the two cores. This results in the generation of $l=2$, $m=1$ gravitational wave modes even before the dominance of a one-arm mode that ultimately arises following merger of the two cores. Our results further suggest that stiffer equations of state give rise to HMNSs generating lower $m=1$ gravitational wave frequencies. Thus, if gravitational waves from the one-arm instability are detected, they could in principle constrain the neutron star equation of state. We estimate that, depending on the equation of state, the one-arm mode could potentially be detectable by second generation gravitational wave detectors at $\sim 10$ Mpc and by third generation ones at $\sim 100$ Mpc. Finally, we provide estimates of the properties of dynamical ejecta, as well as the accompanying kilonovae signatures.

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• Impact of the nuclear symmetry energy on the post-merger phase of a binary neutron star coalescence
• Impact of extreme spins and mass ratios on the post-merger observables of high-mass binary neutron stars
• Revisiting the maximum mass of differentially rotating neutron stars in general relativity: Übermassive stars with realistic equations of state
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• Probing neutron star structure via f-mode oscillations and damping in dynamical spacetime models
• Gravitational Waves from Disks Around Spinning Black Holes: Simulations in Full General Relativity
• Effects of nuclear matter properties in neutron star mergers
• Finite-temperature effects in dynamical-spacetime binary neutron star merger simulations: Validation of the parametric approach
• Revealing Phase Transition in Dense Matter with Gravitational Wave Spectroscopy of Binary Neutron Star Mergers
• Assessing the stability of ultracompact spinning boson stars with nonlinear evolutions
• Effect of magnetic fields on the dynamics and gravitational wave emission of PPI-saturated self-gravitating accretion disks: simulations in full GR
• Self-consistent treatment of thermal effects in neutron-star post-mergers: observational implications for third-generation gravitational-wave detectors
• Probing neutron stars with the full pre-merger and post-merger gravitational wave signal from binary coalescences
• Convective stability analysis of massive neutron stars formed in binary mergers