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

William E. East, Vasileios Paschalidis, Frans Pretorius

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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 ∼10 Mpc and by third generation ones at ∼100 Mpc. Finally, we provide estimates of the properties of dynamical ejecta, as well as the accompanying kilonovae signatures.

Original languageEnglish (US)
Article number244004
JournalClassical and Quantum Gravity
Issue number24
StatePublished - Dec 1 2016

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy (miscellaneous)


  • binary neutron star mergers
  • gravitational waves
  • hypermassive neutron stars
  • kilonovae
  • neutron star equation of state
  • one-arm instability


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