Eccentric Disks from Circumbinary Rings

Abstract: We perform high-resolution, grid-based hydrodynamics simulations of finite gaseous circumbinary rings (CBRs) viscously spreading into disks around binaries. We find that all systems suppress accretion onto the binary when the gas is relatively cold. CBRs display weak variability above the binary orbital frequency $Ωb$ and a dominant, robust spectral peak at $\sim0.1Ω_b$ (half the fiducial lump frequency of $\sim0.2Ω_b$). Smaller rings relax into disks with enhanced gas eccentricity up to $e\simeq 0.3$. We consider the possibility that inefficiently-accreting, intermediate-mass ($\sim10^4 M\odot$) black hole binaries may be sources of quasi-periodic eruptions when rejected streams shock the cavity wall and radiate in the UV or soft X-ray. We discuss the implications of eccentric disks evolved from CBRs for quasar light curves and asymmetric, time-variable double-peaked line emission from disks in galactic nuclei. If binaries drive asymmetry in accretion disk line profiles, our study suggests that the progenitor CBR must have been very compact.