A neutron star merger can result in a massive neutron star which collapses to a black hole after some time. Typically, the black hole will be surrounded by a massive debris disk.

The movie shows an example of this scenario. The initial and merged neutron stars are shown in white, and the black hole as black surface. The colored transparent surfaces highlight surfaces of various mass density in the debris disk.

One can see how the disk is still growing after merger, because the merged neutron star expells matter. As I have shown in a recent publication, this involves complicated fluid flows in the merged star.