Maximum mass for neutron stars

Despite their poor knowledge of the nuclear force, Oppenheimer and Volkoff were able to show unequivocally (Box 5.4) that there is a maximum mass for neutron stars, and it lies between about half a solar mass and several solar masses.

Volkoff found out that if there were no nuclear force in our Universe, then neutron stars would always be less massive than 0.7 solar mass.

Oppenheimer and Volkoffs conclusion cannot have been pleasing to people

like Eddington and Einstein, who found black holes anathema. If Chandrasekhar was to be believed and if Oppenheimer and Volkoff were to be believed (and it was hard to refute them), then neither the white-dwarf graveyard nor the neutronstar graveyard could inter massive stars. Was there any conceivable way at all, then, for massive stars to avoid a black-hole death? Yes; two ways.

First, all massive stars might eject so much matter as they age (for example, by blowing strong winds off their surfaces or by nuclear explosions) that they reduce themselves below 1.4 solar masses and enter the white-dwarf graveyard, or (if one believed Zwicky’s mechanism for supernovae, which few people did) they might eject so much matter in supernova explosions that they reduce themselves below about 1 solar mass during the explosion and wind up in the neutronstar graveyard. 

Second, besides the white-dwarf, neutronstar, and black-hole graveyards, there might be a fourth graveyard for massive stars, a graveyard unknown in the 1930s.

For example, one could imagine a graveyard in Figure 5.3 at circumferences intermediate between neutron stars and white dwarfs—a few hundred or a thousand kilometers. The shrinkage of a massive star might be halted in such a graveyard before the star ever gets small enough to form either a neutron star or a black hole.