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

Understand

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.