The fate of any star is determined by the balance of inward and outward forces within it. Gravity pulls inward and is determined by the star's mass. read more
Really big stars become neutron stars. Really REALLY big stars become black holes. The difference is whether or not the stellar core has sufficient gravity to overcome neutron degeneracy pressure. This is why huge stars become neutron stars: the remnant isn't massive enough to overcome the pressure exerted by neutrons. read more
A simple way for a neutron star to become more massive in order to be able to turn into a black hole is to be part of a binary system, where it is close enough to another star that the neutron star and its binary pair orbit each other, and the neutron star siphons off gas from the other star, thus gaining mass. read more