We investigate the first-order phase transition catalyzed by primordial black holes (PBHs) in the early Universe. We find that superhorizon curvature perturbations generated in this scenario lead to the production of gravitational waves when the scalar modes reenter the horizon. If PBHs with masses about ${10}^{-13}{M}_{\odot }$ constitute all dark matter, then the first-order electroweak phase transition catalyzed by PBHs can explain the gravitational wave signal observed by pulsar timing array collaborations without the overproduction of PBHs.

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• Cosmology
• Dark matter
• Gravitational wave sources