We perform a Bayesian analysis of NANOGrav 15yr and IPTA DR2 pulsar timing
residuals and show that the recently detected stochastic gravitational-wave
background (SGWB) is compatible with a SGWB produced by bubble dynamics during
a cosmological first-order phase transition. The timing data suggests 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 (PBHs) with solar masses. These PBHs 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.Comment: 5 pages, 4 figures + appendice