If the outcome of a neutron star coalescence is a massive neutron star, it shows a complex hydrodynamic evolution before it settles down to a simple rotating neutron star or collapses. It also becomes heated by shock waves formed in the collision.
The movie shows an example for this. The white dots follow the flow of matter, and the blue lines mark their trajectories. The color shows regions heated by shocks in red/yellow. All is shown in a coordinate system rotating together with the orbit of the stars and later the rotation of the merged star.
The two stars have the same mass, but different rotation rates. This leads to a visible asymmetry of the merged object. This state seems to be unstable: after some time, the fluid flow changes into a different pattern. One can also observe some matter leaving the merged object, to become part of the surrounding debris disk (which is not shown).