First-Order Phase Transition Interpretation of Pulsar Timing Array Signal Is Consistent with Solar-Mass Black Holes

We perform a Bayesian analysis of NANOGrav 15-yr and IPTA DR2 pulsar timing residuals and show that the recently detected stochastic gravitational-wave background is compatible with a stochastic gravitational-wave background produced by bubble dynamics during a cosmological first-order phase transition. The timing data suggest that the phase transition would occur around QCD confinement temperature and would have a slow rate of completion. This scenario can naturally lead to the abundant production of primordial black holes with solar masses. These primordial black holes can potentially be detected by current and advanced gravitational-wave detectors LIGO-Virgo-Kagra, Einstein Telescope, Cosmic Explorer, by astrometry with GAIA, and by 21-cm survey.