The Decoupling of Binaries from Their Circumbinary Disks

We have investigated, both analytically and numerically, accreting supermassive black hole binaries as they inspiral due to gravitational radiation elucidate the decoupling of from their disks inform future multi-messenger observations these systems. Our numerical studies evolve equal-mass initial separations $100 GM/c^2$ until merger, resolving scales small $\sim0.04 GM/c^2$, where $M$ is total binary mass. simulations accurately capture point at which orbital evolution each decouples that circumbinary disk, precisely resolve flow gas throughout inspiral. demonstrate numerically timescale-based predictions overestimate occurs by factors $\sim3$, illustrate utility a velocity-based criterion. High-viscosity ($\nu\gtrsim0.03 GM/c$) systems decouple late ($a_b\lesssim 15 GM/c^2$) qualitatively similar morphologies near merger with constant separations. Lower-viscosity earlier exhibit different accretion flows, lead precipitously decreasing onto binary. If detected, such decrease may unambiguously identify host galaxy an ongoing event within LISA error volume. how amplitude variability gradually disks, over course inspirals in band. show that, even when dynamically negligible, leave detectable imprint on phase waves.