In these movies, we place about 100,000 Lagrangian matter tracers that represent fluid elements. The initial distribution of Lagrangian tracers is proportional to the initial mass density. We then calculate the trajectories of the tracers by integrating fluid velocities. The particles are also color-coded according to the density at their current location. In order to appreciate the behavior at the center of the star, we pause in the middle of the evolution and zoom up.

This view shows the inward flow of fluid elements as well as the increase in the density at the center of the collapsing star. An apparent horizon forms and grows in the second half of the simulation.

Note that matter continues to pass through the apparent horizon when the simulation terminates. We infer the final black hole mass and spin to be M_h/M = 0.9 and J_h/M_h² = 0.75