Merger and post-merger of binary neutron stars with a quark-hadron crossover equation of state
Yong-Jia Huang🇨🇳 · Luca Baiotti🇯🇵 · Toru Kojo🇨🇳 · Kentaro Takami🇯🇵 · Hajime Sotani🇯🇵 · Hajime Togashi🇯🇵 · Tetsuo Hatsuda🇯🇵 · Shigehiro Nagataki🇯🇵 · Yi-Zhong Fan🇨🇳
Fully general-relativistic binary-neutron-star (BNS) merger simulations with quark-hadron crossover (QHC) equations of state (EOSs) are studied for the first time. In contrast to EOSs with purely hadronic matter or with a first-order quark-hadron phase transition (1PT), in the transition region QHC EOSs show a peak in sound speed, and thus a stiffening. We study the effects of such stiffening in the merger and post-merger gravitational (GW) signals. Through simulations in the binary-mass range , characteristic differences due to different EOSs appear in the frequency of the main peak of the post-merger GW spectrum (), extracted through Bayesian inference. In particular, we found that (i) for lower-mass binaries, since the maximum baryon number density () after the merger stays below times the nuclear-matter density (), the characteristic stiffening of the QHC models in that density range results in a lower than that computed for the underlying hadronic EOS and thus also than that for EOSs with a 1PT, (ii) for higher-mass binaries, where may exceed depending on the EOS model, whether in QHC models is higher or lower than that in the underlying hadronic model depends on the height of the sound-speed peak. Comparing the values of for different EOSs and BNS masses gives important clues on how to discriminate different types of quark dynamics in the high-density end of EOSs and is relevant to future kilohertz GW observations with third-generation GW detectors.