Studying the speed of sound of dense nuclear matter via the tidal deformability of neutron stars

Abstract

Neutron stars are a natural laboratory for studying dense nuclear matter in its extreme condition. The speed of sound is a microscopic parameter of great interest for studying the equation of state. In this work, we examine possible constraints on the upper bound of the speed of sound.  In our study, we use the measured effective tidal deformability from the two recently detected binary neutron star mergers to impose constraints on the equation of state by using the upper bound on the speed of sound. In our approach, the stiffness of the equation of state is parametrized via two parameters: the speed of sound and the transition density. Moreover, our study is extended in the case of a very massive neutron star, using the recent detection of the GW190814 system. The tidal deformability and the upper bound on the speed of sound for such a massive neutron star are studied. According to our study, such a massive non-rotating neutron star may be existing. Finally, we postulate the kind of future detections that could be useful to impose further constraints and broaden our knowledge on these open problems.