Gravitational-Wave Signature of a First-Order Quantum Chromodynamics Phase Transition in Core-Collapse Supernovae.

A first-order quantum chromodynamics (QCD) phase transition (PT) may take place in the protocompact star (PCS) produced by a core-collapse supernova (CCSN). In this work, we study the consequences of such a PT in a nonrotating CCSN with axisymmetric hydrodynamic simulations. We find that the PT leads to the collapse of the PCS and results in a loud burst of gravitational waves (GWs). The amplitude of this GW burst is ∼30 times larger than the postbounce GW signal normally found for nonrotating CCSN. It shows a broad peak at high frequencies (∼2500-4000  Hz) in the spectrum, has a duration of ≲5  ms, and carries ∼3 orders of magnitude more energy than the other episodes. Also, the peak frequency of the PCS oscillation increases dramatically after the PT-induced collapse. In addition to a second neutrino burst, the GW signal, if detected by the ground-based GW detectors, is decisive evidence of the first-order QCD PT inside CCSNe and provides key information about the structure and dynamics of the PCS.