Masses of neutron stars and blackholes born in close binary systems

Abstract

Abstract The masses of some neutron stars (NSs), blackholes (BHs), radio and X-ray pulsars (PSRs) are known but with very different errors. We collected all of the considerably reliable mass values of these objects and we analysed these values. Using these data number-mass distributions of NSs and BHs are constructed. Among the 44 NSs none of them has a mass value > 2M ⊚. On the other hand, the average mass value for these NSs is very close to 1.4M ⊚. The distribution of the number of NSs with respect to their initial masses has a maximum at a value dose to 1.4M ⊚. We investigated the possibility of explaining very high mass values (∼ 6–10M ⊚) of BHs by accretion in dose binaries. Accretion in binary systems by itself cannot result in considerable changes in masses of compact objects, and one can hardly explain the gap between the masses of NSs and BHs and cannot explain the large masses of BHs. Therefore, the masses of BHs when they were born must be predominantly greater than 3–5M ⊚.