On the Role of Gas Cooling in the Dynamics of Circumbinary Disks

Abstract

Hydrodynamical interactions between binaries and circumbinary disks (CBDs) play an important role in a variety of astrophysical systems, from young stellar binaries to supermassive black hole binaries. Previous simulations of CBDs have mostly employed locally isothermal equation of state. We carry out two-dimensional viscous hydrodynamic simulations of CBDs around equal-mass, circular binaries, treating the gas thermodynamics by thermal relaxation towards equilibrium temperature (the constant-$\beta$ cooling ansatz, where $\beta$ is the cooling time in units of the local Keplerian time). As an initial study, we use the grid-based code Athena++ on a polar grid, covering an extended disk outside the binary co-orbital region. We find that with a longer cooling time, the accretion variability is gradually suppressed, and the morphology of the CBD becomes more symmetric. The disk also shows evidence of hysterisis behavior depending on the initial conditions. Gas cooling also affects the rate of angular momentum transfer between the binary and the CBD, where given our adopted disk thickness and viscosity ($H/r\sim 0.1$ and $\alpha \sim 0.1$), the binary orbit expands while undergoing accretion for most $\beta$ values between 0 and 4.0 except over a narrow range of intermediate $\beta$ values. The validity of using polar grid excising the central domain is also discussed.

14 pages, 12 figures, resubmitted to APJ

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Cited by in corpus (12)

• Long-term Evolution of Binary Orbits Induced by Circumbinary Disks
• Eccentric Binaries in Retrograde Disks
• Disk induced binary precession: Implications for dynamics and multi-messenger observations of black hole binaries
• Magnetically Arrested Circumbinary Accretion Flows
• Viscous circumbinary protoplanetary discs -- I. Structure of the inner cavity
• Suppressed accretion onto massive black hole binaries surrounded by thin disks
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• Radiation Magnetohydrodynamic Simulation of sub-Eddington Circumbinary Disk around an Equal-mass Massive Black Hole Binary
• Decoupling of a supermassive black hole binary from its magnetically arrested circumbinary accretion disk
• Tracking on-the-fly massive black hole binary evolution and coalescence in galaxy simulations: RAMCOAL
• Effects of Thermodynamics on the Concurrent Accretion and Migration of Gas Giants in Protoplanetary Disks
• Insights from Analytical Theory of Eccentric Circumbinary Disks