  Neutron star mergers are cosmic catastrophes that produce some of the most
energetic observed phenomena: short gamma-ray bursts, gravitational wave
signals, and kilonovae. The latter are optical transients, powered by
radioactive nuclides which are synthesized when the neutron-rich ejecta of a
disrupted neutron star undergoes decompression. We model this decompression
phase using data from simulations of post-merger accretion disk winds. We use
smoothed particle hydrodynamics with realistic nuclear heating to model the
expansion over multiple scales, from initially several thousand km to billions
of km. We then render a realistic image of a kilonova ejecta as it would appear
for a nearby observer. This is the first time such a visualization is performed
using input from state-of-the-art accretion disk simulations, nuclear physics
and atomic physics. The volume rendering in our model computes an opacity
transfer function on the basis of the physical opacity, varying significantly
with the inhomogeneity of the neutron richness in the ejecta. Other physical
quantities such as temperature or electron fraction can be visualized using an
independent color transfer function. We discuss several difficulties with the
ParaView application that we encountered during the visualization process, and
give descriptions of our solutions and workarounds which could be used for
future improvements.
