THE MAXIMUM MASS OF A NEUTRON-STAR

Observational identification of black holes as members of binary syste ms requires the knowledge of the upper limit on the gravitational mass of a neutron star. We use modern equations of state for neutron star matter, fitted to experimental nucleon-nucleon scattering data and the properties of light nuclei, to calculate, within the framework of Rho ades & Ruffini (1974), the minimum upper limit on a neutron star mass. Regarding the equation of state as valid up to twice nuclear matter s aturation density, rho(nm) we obtain a secure upper bound on the neutr on star mass equal to 2.9 M.. We also find that in order to reach the lowest possible upper bound of 2.2 M., we need to understand the physi cal properties of neutron matter up to a density of similar to 4 rho(n m).