The discovery a 2 solar mass neutron star (pulsar J1614-2230) created a puzzle for nuclear physicists and astronomers working on the dense matter equation of state. There are various theoretical and experimental hints that at densities a few times the nuclear saturation density (roughly corresponding to the density of a nucleus) a new phase of matter will appear. It may be related to the deconfinement of quarks, of the creation of strange baryons - hyperons. The appearance of new particles hinders the growth of a neutron star mass; theoretical models predicted that a star with exotic particles may collapse to a black hole before reaching 2 Msun.
In recent paper Parameters of rotating neutron stars with and without hyperons by Michał Bejger author studied a selected set of equations of state consistent with the observational constraint from PSR J1614-2230 and show how stars with hyperons in their center differ from these composed of 'standard' matter (neutrons and protons).
The picture presents an artistic vision of Shapiro effect used for pulsar mass estimation.
