Geometry of the collision event. In panel a two stars of mass M₁ and M₂ approach each other with velocities v₁ and v₂ in the frame of the black hole, respectively. In panel b the ejecta has mass M_ej and consists of N equal-mass particles. The ejecta moves around the black hole with relative velocity v_rel. In panel c we switch to the frame of the ejecta, in which each individual particle moves in a random direction with speed |v_rel|.