Can we observe the QCD phase transition-generated gravitational waves through pulsar timing arrays?

Understand

We perform numerical simulations of gravitational waves (GWs) induced by hydrodynamic and hydromagnetic turbulent sources that might have been present at cosmological quantum chromodynamic (QCD) phase transitions.

• For turbulent energies of about 4% of the radiation energy density, the typical scale of such motions may have been a sizable fraction of the Hubble scale at that time.
• The resulting GWs are found to have an energy fraction of about $10^{-9}$ of the critical energy density in the nHz range today and may already have been observed by the NANOGrav collaboration.
• This is further made possible by our findings of shallower spectra proportional to the square root of the frequency for nonhelical hydromagnetic turbulence.