Gas-driven inspiral of binaries in thin accretion disks

Tiede C, Zrake J, MacFadyen A, Haiman Z. 2020. Gas-driven inspiral of binaries in thin accretion disks. The Astrophysical Journal. 900(1), 43.

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Author
Tiede, Christopher; Zrake, Jonathan; MacFadyen, Andrew; Haiman, ZoltánISTA
Abstract
Numerical studies of gas accretion onto supermassive black hole binaries (SMBHBs) have generally been limited to conditions where the circumbinary disk (CBD) is 10-100 times thicker than expected for disks in active galactic nuclei (AGN). This discrepancy arises from technical limitations, and also from publication bias toward replicating fiducial numerical models. Here we present the first systematic study of how the binary's orbital evolution varies with disk scale height. We report three key results: (1) Binary orbital evolution switches from outspiralling for warm disks (aspect ratio ~0.1), to inspiralling for more realistic cooler, thinner disks at a critical aspect ratio ~0.04, corresponding to orbital Mach number ~25. (2) The net torque on the binary arises from a competition between positive torque from gas orbiting close to the black holes, and negative torque from the inner edge of the CBD, which is denser for thinner disks. This leads to increasingly negative net torques on the binary for increasingly thin disks. (3) The accretion rate is modestly suppressed with increasing Mach number. We discuss how our results may influence modeling of the nano-Hz gravitational wave background, as well as estimates of the LISA merger event rate.
Publishing Year
Date Published
2020-08-28
Journal Title
The Astrophysical Journal
Volume
900
Issue
1
Article Number
43
IST-REx-ID

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Tiede C, Zrake J, MacFadyen A, Haiman Z. Gas-driven inspiral of binaries in thin accretion disks. The Astrophysical Journal. 2020;900(1). doi:10.3847/1538-4357/aba432
Tiede, C., Zrake, J., MacFadyen, A., & Haiman, Z. (2020). Gas-driven inspiral of binaries in thin accretion disks. The Astrophysical Journal. American Astronomical Society. https://doi.org/10.3847/1538-4357/aba432
Tiede, Christopher, Jonathan Zrake, Andrew MacFadyen, and Zoltán Haiman. “Gas-Driven Inspiral of Binaries in Thin Accretion Disks.” The Astrophysical Journal. American Astronomical Society, 2020. https://doi.org/10.3847/1538-4357/aba432.
C. Tiede, J. Zrake, A. MacFadyen, and Z. Haiman, “Gas-driven inspiral of binaries in thin accretion disks,” The Astrophysical Journal, vol. 900, no. 1. American Astronomical Society, 2020.
Tiede C, Zrake J, MacFadyen A, Haiman Z. 2020. Gas-driven inspiral of binaries in thin accretion disks. The Astrophysical Journal. 900(1), 43.
Tiede, Christopher, et al. “Gas-Driven Inspiral of Binaries in Thin Accretion Disks.” The Astrophysical Journal, vol. 900, no. 1, 43, American Astronomical Society, 2020, doi:10.3847/1538-4357/aba432.
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