Fast Ejecta from Binary Neutron Star Mergers

• Author / Creator

  Dean, Coleman

• We investigate the production of fast ejecta from the contact interface in coalescing binary neutron stars. This ejecta expands rapidly enough (velocities > 0.6c) that the r-process freezes out, generating an ultraviolet precursor to the kilonova powered by the decay of free neutrons. Previous work using grid-based simulations has reached inconclusive results about the amount of this fast ejecta produced in the merger, partly due to an inability to numerically resolve the surface layers of the colliding stars. These results stand in contrast to those from simulations using particle-based hydrodynamic methods (SPH), which yield much higher values of free neutron ejecta. Here we report the development and preliminary results of axisymmetric grid-based merger simulations that include the dominant physics in approximate form in order to examine the production of these ejecta at high resolutions not achievable in three dimensional models. At the resolutions studied thus far ({281.3, 140.6,70.3} m equivalent to {2.2, 1.1, 0.56} % of the stellar radius, or ∼{70.3, 35.2,17.6} times the pressure scale height at 99% of the neutron star radius), we find that the mass of fast ejecta has only a weak resolution dependence, suggesting that simulations of this ejecta component may be close to converging. Our results therefore cannot yet resolve the tension in ejecta masses produced by SPH and grid-based binary neutron star merger simulations as a pure numerical resolution effect.

• Subjects / Keywords

  • Dense Matter
  • Stars: Neutron
  • Equation of State
  • Hydrodynamics
  • Shock Waves
  • Stars

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-1xq3-6g05

• License

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