  We study the gravitational waves produced by the collision of the bubbles as
a probe for the cosmological first order QCD phase transition, considering
heavy static quarks. Using AdS/QCD and the correspondence between a first order
Hawking-Page phase transition and confinement-deconfinement phase transition,
we find the spectrum and the strain amplitude of the gravitational wave within
the hard and soft wall models. We postulate the duration of the phase
transition corresponds to the evaporation time of the black hole in the five
dimensional dual gravity space, and thereby obtain a bound on the string length
in the space and correspondingly on the duration of the QCD phase transition.
We also show that IPTA and SKA detectors will be able to detect these
gravitational waves, which can be an evidence for the first order deconfinement
transition.
