The evolution of large cavities and disc eccentricity in circumbinary discs

Abstract

We study the mutual evolution of the orbital properties of high mass ratio, circular, co-planar binaries and their surrounding discs, using 3D Smoothed Particle Hydrodynamics simulations. We investigate the evolution of binary and disc eccentricity, cavity structure and the formation of orbiting azimuthal over-dense features in the disc. Even with circular initial conditions, all discs with mass ratios q > 0.05 develop eccentricity. We find that disc eccentricity grows abruptly after a relatively long time-scale (∼400–700 binary orbits), and is associated with a very small increase in the binary eccentricity. When disc eccentricity grows, the cavity semi-major axis reaches values acav ≈ 3.5 abin. We also find that the disc eccentricity correlates linearly with the cavity size. Viscosity and orbit crossing, appear to be responsible for halting the disc eccentricity growth – eccentricity at the cavity edge in the range ecav ∼ 0.05–0.35. Our analysis shows that the current theoretical framework cannot fully explain the origin of these evolutionary features when the binary is almost circular (ebin ≲ 0.01); we speculate about alternative explanations. As previously observed, we find that the disc develops an azimuthal over-dense feature in Keplerian motion at the edge of the cavity. A low contrast over-density still co-moves with the flow after 2000 binary orbits; such an over-density can in principle cause significant dust trapping, with important consequences for protoplanetary disc observations.

A Survey of Disc Thickness and Viscosity in Circumbinary Accretion: Binary Evolution, Variability, and Disc Morphology

“…Eccentric circumbinary discs are commonly observed in stellar binaries such as GG Tauri A (Guilloteau et al 1999;McCabe et al 2002;Andrews et al 2014;Keppler et al 2020), and are commonly found in numerical simulations (e.g. Miranda et al 2017;MacFadyen & Milosavljević 2008;Ragusa et al 2020) of binaries with mass ratios 𝑞 0.04 (D'Orazio et al 2016;Duffell et al 2020). The eccentric discs can precess coherently (Miranda et al 2017;Ragusa et al 2020), which is consistent with the existence of trapped eccentric modes in circumbinary discs (Muñoz & Lithwick 2020).…”

“…This scaling follows from a linear analysis, balancing torques from waves excited at Lindblad resonances with the viscous torque in the disc (Artymowicz & Lubow 1994;Miranda & Lai 2015;Lubow et al 2015), although these anal-yses are commonly found to under-predict cavity sizes when compared with numerical simulations (e.g. MacFadyen & Milosavljević 2008;Ragusa et al 2020), and should be taken at most as a general guideline (Miranda & Lai 2015). Especially at low viscosity, the cavity extends to a larger radius at high Mach number.…”

“…The M > 10 regime has been explored more sparsely (e.g. Farris et al 2015;D'Orazio et al 2016;Ragusa et al 2016;Tiede et al 2020;Heath & Nixon 2020;Ragusa et al 2020), with only a subset of these studies exploring orbital evolution as a function of Mach number (Tiede et al 2020;Heath & Nixon 2020). Both studies found that inspirals occur at higher Mach number and simulated finite accretion discs, allowing the discs to spread viscously, without a steady supply of gas from large radii.…”

Vortex-like kinematic signal, spirals, and beam smearing effect in the HD 142527 disk

“…More recently, numeric simulations have also shown that a companion with a mass ratio q ≥ 0.05 can create an eccentric cavity and trigger an azimuthal clump in the gas (Shi et al 2012;Ragusa et al 2017). For even larger mass ratios, the azimuthal gas contrast may reach a value between two and four in steady state, similar to what is observed in HD 142527 (Price et al 2018;Ragusa et al 2020). Performed with a relatively high turbulent viscosity (α ∼ 5 × 10 −3 ), these simulations did not produce vortices but were still able to trap dust particles in the gas clump, which is rotating at Keplerian velocity.…”

“…While not mutually exclusive, another theory suggests that an azimuthal gas pressure maximum can be formed by the interaction between a binary, with a mass ratio q 0.05 with the main star, and the circumbinary disk. Numerical simulations have shown that the massive companion would create a large and eccentric cavity, leading to a gas asymmetry in the gas (Shi et al 2012;D'Orazio et al 2016;Ragusa et al 2017;Price et al 2018) rotating at Keplerian velocity and able to trap dust particles (Calcino et al 2019;Ragusa et al 2020).…”