We investigate the effect of dynamically coupling gas torques with gravitational wave (GW) emission during the orbital evolution of an equal-mass massive black hole binary (MBHB). We perform hydrodynamical simulations of eccentric MBHBs with total mass M = 10 ^6 M ⊙ embedded in a prograde locally isothermal circumbinary disk (CBD). We evolve the binary from 55 to 49 Schwarzschild radii separations using up to 2. 5 post-Newtonian corrections to the binary dynamics, which allow us to follow the GW-driven inspiral. For the first time, we report the measurement of gas torques onto a live binary a few years before the merger, with and without concurrent GW radiation. We also report the gas-induced orbital dephasing δϕ ₎ₑ₁ ∼ −0. 007 rad over 278 orbital cycles that is likely driven mainly by disk-induced precession, and LISA should be able to detect it at redshift z = 1. Our results show how GWs alone can be used to probe the astrophysical properties of CBDs and have important implications for multimessenger strategies aimed at studying the environments of MBHBs.
Garg et al. (Thu,) studied this question.