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Abstract

The first multimessenger observation attributed to a merging neutron star
binary provided an enormous amount of observational data. Unlocking the full
potential of this data requires a better understanding of the merger process
and the early post-merger phase, which are crucial for the later evolution that
eventually leads to observable counterparts. In this work, we perform standard
hydrodynamical numerical simulations of a system compatible with GW170817. We
focus on a single equation of state (EOS) and two mass ratios, while neglecting
magnetic fields and neutrino radiation. We then apply newly developed
postprocessing and visualization techniques to the results obtained for this
basic setting. The focus lies on understanding the three-dimensional structure
of the remnant, most notably the fluid flow pattern, and its evolution until
collapse. We investigate the evolution of mass and angular momentum
distribution up to collapse, as well as the differential rotation along and
perpendicular to the equatorial plane. For the cases that we studied, the
remnant cannot be adequately modeled as a differentially rotating axisymetric
NS. Further, the dominant aspect leading to collapse is the GW radiation and
not internal redistribution of angular momentum. We relate features of the
gravitational wave signal to the evolution of the merger remnant, and make the
waveforms publicly available. Finally, we find that the three-dimensional
vorticity field inside the disk is dominated by medium-scale perturbances and
not the orbital velocity, with potential consequences for magnetic field
amplification effects.