  We search for a first-order phase transition gravitational wave signal in 45
pulsars from the NANOGrav 12.5 year dataset. We find that the data can be
explained in terms of a strong first order phase transition taking place at
temperatures below the electroweak scale. In our search, we find that the
signal from a first order phase transition is degenerate with that generated by
Supermassive Black Hole Binary mergers. An interesting open question is how
well gravitational wave observatories could separate such signals.
