Specific angular momentum distribution of the mass shells of the primary star in the example binary shown in Figure 1, at core carbon depletion in red. The kink at ≃7.8 M_⊙ is the transition between the carbon-oxygen core and helium shell. It forms an accretion disk of 1.46 M_⊙ during the collapse. For comparison, we plot the specific angular momentum of the ISCO, j_ISCO, for a non-rotating Schwarzshild BH (dashed black) and a maximally rotating Kerr BH (dotted black), as a function of BH mass. Additionally, we track the evolution of j_ISCO for the example primary during the collapse as its mass and spin change (dashed green). It tracks j_ISCO at the collapse of each mass shell and starts at 3 M_⊙ with a BH of 2.5 M_⊙ and 0.5 M_⊙ neutrino mass loss.