Neutron stars are supported against gravitational collapse by neutron degeneracy pressure. This pressure arises from the Pauli exclusion principle, which prevents neutrons from occupying the same quantum state. As the density of a neutron star increases, the neutrons are forced closer together and the degeneracy pressure becomes stronger. However, at very high densities, the neutron degeneracy pressure becomes insufficient to support the star against gravitational collapse.
The exact maximum mass of a neutron star depends on a number of factors, including the composition of the star and the equation of state of nuclear matter. However, most estimates suggest that the maximum mass is about 2-3 solar masses.
If the mass of a neutron star exceeds this limit, it will collapse into a black hole. A black hole is a region of spacetime with such strong gravitational forces that nothing, not even light, can escape from it. Neutron stars that collapse into black holes are thought to be the progenitors of stellar-mass black holes.
