The evolution of a binary in a retrograde circular orbit embedded in an accretion disk

Abstract

Supermassive black hole binaries may form as a consequence of galaxy mergers. Both prograde and retrograde orbits have been proposed. We study a binary of a small mass ratio, q, in a retrograde orbit immersed in and interacting with a gaseous accretion disk in order to estimate time scales for inward migration leading to coalescence and the accretion rate to the secondary component. We employ both semi-analytic methods and two dimensional numerical simulations, focusing on the case where the binary mass ratio is small but large enough to significantly perturb the disk. We develop the theory of type I migration for this case and determine conditions for gap formation finding that then inward migration occurs on a time scale equal to the time required for one half of the secondary mass to be accreted through the unperturbed disk, with accretion onto the secondary playing only a minor role. The semi-analytic and fully numerical approaches are in good agreement, the former being applicable over long time scales. Inward migration induced by interaction with the disk alleviates the final parsec problem. Accretion onto the secondary does not significantly affect the orbital evolution, but may have observational consequences for high accretion efficiency. The binary may then appear as two sources of radiation rotating around each other. This study should be extended to consider orbits with significant eccentricity and the effects of gravitational radiation at small length scales. Note too that torques acting between a circumbinary disk and a retrograde binary orbit may cause the mutual inclination to increase on a timescale that can be similar to, or smaller than that for orbital evolution, depending on detailed parameters. This is also an aspect for future study (abridged).

24 pages, 18 figures, accepted for publication in A&A. For movies of the simulations see http://astro.qmul.ac.uk/people/sijme-jan-paardekooper/publications

References in corpus (8)

• Massive black hole binary mergers within sub-pc scale gas discs
• The Population of Viscosity- and Gravitational Wave-Driven Supermassive Black Hole Binaries Among Luminous AGN
• Intermediate mass black holes in AGN disks II. Model predictions & observational constraints
• Observable Signatures of a Black Hole Ejected by Gravitational Radiation Recoil in a Galaxy Merger
• Binary black hole mergers in gaseous disks: Simulations in general relativity
• Modeling of Emission Signatures of Massive Black Hole Binaries: I Methods
• On the width and shape of the corotation region for low-mass planets
• Epicyclic Motions and Standing Shocks in Numerically Simulated Tilted Black-Hole Accretion Disks

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• Estimating the depth of gaps opened by planets in eccentric orbit