Black Hole

Neutron degeneracy pressure cannot support an object having mass greater than 2-3 solar masses. Sometimes not all the matter outside the 1.4 solar mass core gets blown away in the type II supernova. Sometimes some of the matter falls back down onto the collapsed core. This makes the core too massive to hold itself up at all, so it collapses even more. This probably happens for most stars which started out with > 20 solar masses.

Once the neutron degeneracy pressure is overcome, there is no force that can halt the collapse. Once the object collapses to compact enough size, the escape velocity at the surface becomes greater than the speed of light. At this point, we have have a black hole. Nothing can escape -- not even light!

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