Orbital Evolution of Binaries in Circumbinary Disks

I will present the to-date largest parameter space exploration of multi-scale binaries in circumbinary disks (CBDs), deriving orbital evolution prescriptions for eccentric, unequal mass binaries from a suite of 2D hydrodynamic simulations run with Arepo. I will show that binary eccentricities evolve towards steady state values that increase with mass ratio, and saturate at an equilibrium eccentricity e_{b,eq} ~ 0.5 in the large mass ratio regime. This result is in line with resonant theory. For binaries accreting at their combined Eddington limit, a steady state eccentricity can be achieved within a few Megayears. Once at their steady state eccentricities, binaries with mass ratios greater than q_b > 0.3 evolve towards coalescence, while lower mass ratio systems expand due to CBD torques. I will discuss implications for population studies of massive black hole binaries, protostars in binary systems, and post-common envelope binaries observed by ground-based gravitational wave detectors.