Catastrophic mini-collapse for two configurations with different values of angular momentum J at the edge of the instability region, on the gravitational mass–equatorial radius M−R_eq plane. For an isolated star, the left panel shows the trajectory along a line of constant baryon mass M_b (note the arrow is inclined, since the ordinate is M, not M_b) to another stable NS configuration with J equal to the initial one. Right panel: if the angular momentum is larger than some critical value that depends on the EOS, the star collapses directly to a BH, since the mass of the twin branch counterpart is too low.