Hydrodynamic simulations reveal stellar captures produce eccentric black-hole binaries merging in ~10 hours

The study combines smoothed-particle hydrodynamics of gas dynamical friction with semianalytic three-body integrations to track sequential black-hole captures inside massive main-sequence stars. Black holes below 20 percent of the stellar mass settle into quasi-hydrostatic BH* configurations; a second capture at small impact parameter then embeds a compact binary inside the envelope. Gas drag rapidly raises eccentricity while shrinking the orbit until gravitational-wave emission dominates at high frequency. Resulting mergers occur on timescales of roughly ten hours, far shorter than isolated binary evolution channels. This pathway operates efficiently in star clusters and AGN disks and extends naturally to Thorne-Żytkow objects. The mechanism supplies a concrete dynamical route to the high-eccentricity mergers that LIGO and LISA could distinguish from circularized field binaries. Prior population-synthesis studies largely omitted sequential captures inside common envelopes, underestimating the contribution of this channel. The new simulations indicate that residual eccentricity above 0.9 at 10 Hz remains detectable even after partial circularization, providing an observable discriminant. Next steps require embedding these capture cross-sections into full cluster and AGN-disk population models to forecast event rates and eccentricity distributions for LIGO O5 and LISA. Targeted searches for eccentric triggers in existing LIGO data and hydrodynamical resolution studies of envelope ejection will test whether the binaries survive to merger or are disrupted.