A Novel Formation Channel for Supermassive Black Hole Binaries in the Early Universe via Primordial Black Holes

We present a novel formation channel for supermassive black hole (SMBH) binaries in the early Universe, driven by primordial black holes (PBHs). Using high-resolution hydrodynamical simulations, we explore the role of massive PBHs ($m_{\rm BH} \sim 10^6 M_\odot$) in catalyzing the formation of direct-collapse black holes (DCBHs), providing a natural in situ pathway for binary SMBH formation. PBHs enhance local overdensities, accelerate structure formation, and exert thermal feedback on the surrounding medium via accretion. Lyman-Werner (LW) radiation from accreting PBHs suppresses H$2$ cooling, shifting the dominant gas coolant to atomic hydrogen. When combined with significant baryon--dark matter streaming velocities ($v_{\rm bχ} \gtrsim 0.8 σ_{\rm bχ}$, where $σ_{\rm bχ}$ is the root-mean-square streaming velocity), these effects facilitate the formation of dense, gravitationally unstable, atomically cooling gas clouds in the PBH wake. These clouds exhibit sustained high inflow rates ($\dot{M}_{\rm infall} \gtrsim 10^{-2}-10^{-1} M_\odot \mathrm{yr}^{-1}$), providing ideal conditions for DCBH formation from rapidly growing supermassive stars of $\sim 10^5 M_\odot$ at redshift $z\sim 10-20$. The resulting systems form SMBH binaries with initial mass ratios $q\sim O(0.1)$ and separations of $\sim 10$ pc. Such PBH--DCBH binaries provide testable predictions for JWST and ALMA, potentially explaining high-$z$ sources such as Little Red Dots, and represent gravitational-wave sources for future missions like LISA and TianQin, bridging early-Universe black hole physics, multi-messenger astronomy, and dark matter theory.