Constraints on speed of sound within neutron stars

With the advancement of multi-messenger astronomical observation techniques, observational data have been providing us crucial constraints for understanding the properties of dense nuclear matter. Additionally, measurements on the neutron skin thickness in finite nuclei have also imposed new constraints on the nuclear equations of state (EoS). The speed of sound in neutron stars naturally bridges nuclear matter and quark matter, thus it has become an effective approach for studying the EoS of dense nuclear matter. In this work, we constructed different speed-of-sound profiles in the dense region and investigated the constraints provided by neutron star mass, radius, and dimensionless tidal deformability on the nuclear EoS. Notably, by incorporating experimental results of neutron skin thickness in finite nuclei, the screened speed-of-sound profiles reveal the exotic of a softening slope followed by a hardening rise, and we further discussed the possible phase transition processes. We also present a discussion on the possible ultra-light neutron star in the supernova remnant HESS J1731-347.