What is the maximum mass limit for a neutron star before collapsing into a black hole?

The maximum mass limit for a neutron star before collapse is called the Tolman–Oppenheimer–Volkoff limit. It is the theoretical upper mass boundary for a cold, non-rotating neutron star, where gravity can no longer be balanced by pressure and the properties of ultradense nuclear matter.

The limit is named for Richard Chace Tolman and the physicists J. Robert Oppenheimer and George Volkoff. Their pioneering 1939 calculation produced a value of roughly 0.7 solar masses, but it treated the star as an idealized gas of non-interacting neutrons. Modern models include strong nuclear forces and produce substantially higher estimates, commonly around 2.2 to 2.9 solar masses.

There is no single perfectly measured number because the equation of state of matter at neutron-star densities remains uncertain. Rotation can also temporarily raise the supported mass, by roughly 18–20% for rigid rotation. The Chandrasekhar limit is the analogous limit for white dwarfs, not neutron stars; the Eddington limit concerns radiation pressure, while the Roche limit concerns tidal disruption.