The speed of sound in the zero temperature QCD phase diagram

Information from both nuclear theories and astrophysical observations are combined to shed light on the speed of sound across the zero-temperature QCD phase diagram. While calculations based on chiral effective field theory at low densities and measurements of neutron star masses, radii, and tidal deformabilities already provided valuable insights into the neutron star equations of state, predictions of perturbative QCD at ultra-high densities can impose additional constraints orthogonal to those previously reported. Furthermore, information about the phase of matter in the intermediate region that lies beyond the most massive neutron stars and below where perturbative QCD applies may be extracted, opening the possibility of a holistic view of the zero-temperature QCD phase diagram. Prospects of placing bounds on the maximum and minimum speed of sound within and beyond neutron star densities is forecasted based on anticipated astrophysical observations.