Under what condition does a remnant core collapse completely into a black hole?

Answer

If the remnant core exceeds the upper mass boundary defined by the Tolman-Oppenheimer-Volkoff limit

If the mass of the surviving core surpasses the critical upper limit, gravity completely overcomes even the neutron degeneracy pressure, leading to a complete collapse into a black hole.

Under what condition does a remnant core collapse completely into a black hole?
starsupernovaneutron starblack holeremnant