On the mass distribution of neutron stars

The distribution of masses for neutron stars is analysed using the Bayesian statistical inference, evaluating the likelihood of the proposed Gaussian peaks by using 54 measured points obtained in a variety of systems. The results strongly suggest the existence of a bimodal distribution of the masses, with the first peak around 1.37 M⊙ and a much wider second peak at 1.73 M⊙. The results support earlier views related to the different evolutionary histories of the members for the first two peaks, which produces a natural separation (even if no attempt to ‘label’ the systems has been made here). They also accommodate the recent findings of ∼M⊙ masses quite naturally. Finally, we explore the existence of a subgroup around 1.25 M⊙, finding weak, if any, evidence for it. This recently claimed low-mass subgroup, possibly related to the O–Mg–Ne core collapse events, has a monotonically decreasing likelihood and does not stand out clearly from the rest of the sample.