Oppenheimer-Volkoff limit

relationship between the mass of a degenerate star and its radius

The Oppenheimer-Volkoff limit is the upper limit for the mass of a neutron star beyond which it must collapse to become a black hole or, possibly, a quark star. Its value is not known exactly because the properties of neutron degenerate matter can only be estimated, but it is generally thought to be between 2 and 3 solar masses.