Final answer:
A neutron star is stopped from becoming a black hole by neutron degeneracy pressure, but if its mass exceeds about 2-3 solar masses, not even this pressure can resist the force of gravity, leading to the star's collapse into a black hole.
Step-by-step explanation:
A neutron star is prevented from collapsing into a black hole due to the resistance provided by neutron degeneracy pressure, which is akin to the Pauli exclusion principle that prevents fermions (particles like neutrons) from occupying the same quantum state. When a star's core collapses, and its mass is too great, not even this neutron degeneracy pressure can halt the collapse, leading to the formation of a black hole. However, the upper mass limit for a neutron star to avoid collapsing into a black hole is not precisely known, though it is thought to be around 2-3 solar masses.
If the core's mass exceeds this limit, gravity overwhelms all other forces and continues to crush the core, leading to the creation of a black hole. This phenomenon is characterized by an intense gravitational field that significantly affects matter and energy, often observable through effects such as X-ray emissions in binary star systems. Neutron stars themselves are incredibly dense objects formed from the remnants of supernova explosions where the core's electrons and protons merge into neutrons.