Using massive neutron stars to constrain dense matter Equation of State

 Mass measurement of neutron stars has proved to be a useful tool to probe  the composition of dense matter above nuclear saturation density. It is believed that if strangeness-bearing exotic components such as hyperons are present in the neutron star interior, they would soften the equation of state (EoS) and hence result in a lower maximum neutron star mass. However, the recent discovery of massive compact stars such as PSR J1614-2230 contradicts the existence of exotic matter in the core. On the other hand, kaon production at sub-threshold densities in heavy-ion collisions, which is another robust tool to probe stiffness of nuclear matter at suprasaturation densities, indicates a soft EoS upto 2-3 times nuclear saturation density.
Motivated by the recent observational data on neutron star masses, we carefully re-examined the conditions for appearance of hyperons in the interior of neutron stars. Our investigation pointed to the result that maximum neutron star masses decrease with the strangeness content of the core linearly, independent of the nuclear EoS. Pulsar mass measurements can then be used to constrain hyperon fractions in neutron stars. We also studied the implications of the heavy-ion results on properties of compact stars. Starting from the soft EoS and connecting it smoothly to the stiffest causal EoS, we calculated the maximally allowed gravitational mass of a compact star.