Viscous-Dynamical Ejecta from Binary Neutron Star Merger

Understand

General-relativistic simulations of binary neutron star mergers with viscosity reveal a new outflow mechanism operating in unequal mass binaries on dynamical timescales and enabled by turbulent viscosity.

• These "viscous-dynamical" ejecta are launched during merger due to the thermalization of mass exchange streams between the secondary and the primary neutron star.
• They are characterized by asymptotic velocities extending up to ${\sim} 0.8\, c$, and have masses that depend on the efficiency of the viscous mechanism.
• Depending on the unknown strength of the effective viscosity arising from magnetohydrodynamics instabilities operating during merger, the overall mass of the dynamical ejecta could be enhanced by a factor of a few and the mass of the fast tail of the ejecta having asymptotic velocities $\geq 0.6\, c$ by up to four orders of magnitude.