Kelvin–Helmholtz instability of counter-rotating discs

Quach, D.; Dyda, Sergei; Lovelace, R. V. E.

doi:10.1093/mnras/stu2130

Cited by 10 publications

(9 citation statements)

References 19 publications

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“…Important future work will be full 3D hydrodynamic simulations including the heating, cooling, and radiative transfer of the gas of counter-rotating discs. This will account for the supersonic Kelvin-Helmholtz instability, which is a 3D instability, as well as the strong shocks which it induces (see Quach et al 2014). The time-scale of mixing of the two components and their loss of angular momentum is expected to be shortened compared with the present results.…”

Section: Discussionmentioning

confidence: 99%

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Counter-rotating accretion discs

Dyda

Lovelace

Ustyugova

et al. 2014

Monthly Notices of the Royal Astronomical Society

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Counter-rotating discs can arise from the accretion of a counter-rotating gas cloud onto the surface of an existing co-rotating disc or from the counter-rotating gas moving radially inward to the outer edge of an existing disc. At the interface, the two components mix to produce gas or plasma with zero net angular momentum which tends to free-fall towards the disc center. We discuss high-resolution axisymmetric hydrodynamic simulations of viscous counter-rotating disc for cases where the two components are vertically separated and radially separated. The viscosity is described by an isotropic α−viscosity including all terms in the viscous stress tensor. For the vertically separated components a shear layer forms between them the middle of this layer in free-fall to the disc center. The accretion rates are increased by factors ∼ 10 2 − 10 4 over that for a conventional disc rotating in one direction with the same viscosity. The vertical width of the shear layer and the accretion rate are strongly dependent on the viscosity and the mass fraction of the counter-rotating gas. In the case of radially separated components where the inner disc co-rotates and the outer disc rotates in the opposite direction, a gap between the two components opens and closes quasi-periodically. The accretion rates are 25 times larger than those for a disc rotating in one direction with the same viscosity.

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Section: Discussionmentioning

confidence: 99%

“…This can account roughly for the factor of 3. Note that at the interface between the oppositely rotating components there can be a strong supersonic Kelvin-Helmholtz instability (Quach, Dyda, & Lovelace 2014) which locally increases the turbulent viscosity coefficient by a large factor.…”

Section: Vertically Offset Torusmentioning

confidence: 99%

Counter-rotating accretion discs

Dyda

Lovelace

Ustyugova

et al. 2014

Monthly Notices of the Royal Astronomical Society

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“…2pc yrs through efficient annihilation of angular momentum (AM) simply estimated by the linear analysis (Quach et al 2015), where R 2pc = R/2 pc is the radius of disc and M 7 = M • /10 7 M is the black hole mass. This is the KH catastrophe of the CRD in NGC 1068.…”

Section: Anatomy Of the Cbd In Ngc 1068mentioning

confidence: 99%

“…On the other hand, this indicates that there were a series of CRDs across cosmic time. The CRD will give rise to very fast accretion onto SMBHs [also see Ref (Kuznetsov et al 1999;Quach et al 2015;Dyda et al 2015)] and show some imprints at scale of a few parsec. Is there any independent evidence for this?…”

Section: A Crd Around a Single Smbhmentioning

confidence: 99%

“…For simplicity, we apply the Rankine-Hugoniot calculation to the slab geometry of the CRD in this paper, allowing us to focus on analysis of the major effects of the KHI action and tidal interaction of the CB-SMBHs with its circumbinary disk in a simple way. Following Quach et al (2015) and Dyda et al (2015), we will make use of disc geometry of the counter-rotating gas for detailed analysis of the KHI and its effects in the future. The violent dissipation of the kinetic energies of the counter-rotating motion gives rise to gas expansion in the vertical direction so that we have to study 3-dimensional processes, such as outflows from the disc surface, which could be probably related with the observed in this region.…”

Section: Disc Geometrymentioning

confidence: 99%

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Dynamical evidence of the sub-parsec counter-rotating disc for a close binary of supermassive black holes in the nucleus of NGC 1068

Wang,

Songsheng,

et al. 2020

Preprint

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A puzzle in NGC 1068 is how to secularly maintain the counter-rotating disc (CRD) from 0.2 to 7 pc unambiguously detected by recent ALMA observations of molecular gas. Upon further dynamical analysis, we find that the Kelvin-Helmholtz (KH) instability (KHI) results in an unavoidable catastrophe for the disc developed at the interface between the reversely rotating parts. We demonstrate that a close binary of supermassive black holes provides tidal torques to prevent the disc from the KH catastrophe and are led to the conclusion that there is a binary black hole at the center of NGC 1068. The binary is composed of black holes with a separation of 0.1 pc from GRAVITY/VLTI observations, a total mass of 1.3 × 10 7 M and a mass ratio of ∼ 0.3 estimated from the angular momentum budget of the global system. The KHI gives rise to a gap without cold gas at the velocity interface which overlaps with the observed gap of hot and cold dust regions. Releases of kinetic energies from the KHI of the disc are in agreement with observed emissions in radio and γ-rays. Such a binary is shrinking on a timescale much longer than the local Hubble time via gravitational waves, however, the KHI leads to an efficient annihilation of the orbital angular momentum and a speed up merge of the binary, providing a new mechanism for solving the long standing issue of "final parsec problem". Future observations of GRAVITY + /VLTI are expected to be able to spatially resolve the CB-SMBHs suggested in this paper.

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The instability of viscous self-gravitating protostellar disk affected by density bump

Elyasi

Nejad-Asghar

2017

Astrophys Space Sci

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Kelvin–Helmholtz instability of counter-rotating discs

Cited by 10 publications

References 19 publications

Counter-rotating accretion discs

Counter-rotating accretion discs

Dynamical evidence of the sub-parsec counter-rotating disc for a close binary of supermassive black holes in the nucleus of NGC 1068

The instability of viscous self-gravitating protostellar disk affected by density bump

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