The Tolman–Oppenheimer–Volkoff limit, which is the neutron degeneracy pressure. Similarly, a neutron star is formed when a star large enough fuses enough iron so that its core exceeds the Chandrasekhar limit, which is the electron degeneracy pressure, the core collapses, and you get a neutron star. If this neutron star is greater than the Tolman–Oppenheimer–Volkoff limit, you get a black hole or (possibly) a quark star.