Article
Astronomy & Astrophysics
Karamveer Kaur, Nicholas C. Stone, Shmuel Gilbaum
Summary: The classical radiation pressure instability is a persistent theoretical feature of thin, radiatively efficient accretion discs. Limited evidence of this instability has been observed in nature, such as rapid heartbeat oscillations and quasi-periodic eruptions in X-ray binaries. However, in tidal disruption events, the occurrence of this instability is not clear. By constructing steady state 1D models of thin magnetic accretion discs, we explain the absence of instability in tidal disruption events and the short periods of quasi-periodic eruptions.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Oscar M. Pimentel Diaz, P. Chris Fragile, F. D. Lora-Clavijo, Bridget Ierace, Deepika Bollimpalli
Summary: The study investigates the impact of magnetic susceptibility on magneto-rotational instability (MRI) within the context of black hole accretion, finding that paramagnetic discs exhibit shorter wavelength and faster growth rate for unstable modes compared to diamagnetic discs. Additionally, the magnetization parameter in the saturated state is predicted to be smaller in paramagnetic discs. Numerical simulations confirm these predictions, showing higher vertically integrated stress and mass accretion rate in paramagnetic discs compared to diamagnetic discs.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Marius Lehmann, Min-Kai Lin
Summary: Protoplanetary discs can exhibit various instabilities, such as the vertical shear instability, convective overstability, streaming instability, and dust settling instability. The behaviors of these instabilities under different conditions are not well understood. In this study, we develop a model of a non-isothermal gas interacting with dust and find that dust inhibits the vertical shear instability and convective overstability, while the gas' radial buoyancy suppresses the streaming instability at certain scales. Additionally, we identify novel instabilities unique to a dusty non-isothermal gas. These findings may have implications for planetesimal formation.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Matthew S. B. Coleman, Roman R. Rafikov, Alexander A. Philippov
Summary: This study numerically explores different wave modes operating near the boundary layer in accretion discs, focusing on their morphological characteristics. The research provides insights into the angular momentum and mass transport across the boundary layer, as well as emission variability in accreting objects. New types of modes, including global spiral density waves, were discovered in the study, shedding light on the dynamics of accretion processes.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Matthew S. B. Coleman, Roman R. Rafikov, Alexander A. Philippov
Summary: This study examines the characteristics of angular momentum transport produced by different types of wave modes in the boundary layers of astrophysical objects. The results show the important contribution of correlated perturbations to the mass accretion rate and a clear correlation between the angular momentum flux injected by the waves and the mass accretion rate through the boundary layer. This research provides insights into wave-mediated transport in future studies of the boundary layers using three-dimensional, magnetohydrodynamic approaches.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Loren E. Held, Henrik N. Latter
Summary: The study reveals through numerical simulations that turbulent stress oscillations can lag behind pressure oscillations by approximately 5 orbits in certain cases, with implications for understanding thermal and viscous overstability in discs around compact objects.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Robert J. Teed, Henrik N. Latter
Summary: Oscillatory convection (COS) is an important dynamical process in protoplanetary discs, reshaping the thermal structure and mixing solid material in different saturation states as Reynolds and Richardson numbers increase. The system evolves from weak non-linear waves to wave turbulence and then to the formation of persistent zonal flows in three dimensions, potentially spawning vortices in the orbital plane.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Loren E. Held, George Mamatsashvili
Summary: This study investigates the effect of the large magnetic Prandtl number on the magnetorotational instability (MRI) and turbulent transport. The results show that at large Pm, the turbulent energy and stress plateau, no longer depending on Pm. The analysis of the turbulent dynamics in Fourier space helps to understand these findings.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Hongping Deng, Gordon Ogilvie, Lucio Mayer
Summary: Warped accretion discs of low viscosity are prone to hydrodynamic instability due to parametric resonance of inertial waves as confirmed by local simulations, but global simulations have not shown such instability. Utilizing a new hybrid Godunov-type Lagrangian method, global simulations were able to capture the instability and demonstrate the effects of turbulence on the warp.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Mitchell C. Begelman, Nicolas Scepi, Jason Dexter
Summary: Magnetically arrested accretion discs (MADs) are a magnetic phenomenon around black holes that can generate powerful jets and explain observations of black hole environments. We propose a new theoretical model that suggests it is mainly a toroidal field that defines and regulates the properties of MADs. We confirm the plausibility of our model through simulations and suggest criteria to distinguish MADs from other accretion states.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
V. V. Zhuravlev
Summary: Research shows that gas-dust perturbations in a disc with dust settling exhibit non-linear three-wave resonant interactions. Taking into account the back reaction of the dust on the gas, the amplitudes of the waves explosively grow simultaneously, which may facilitate dust clumping and the formation of planetesimals.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Shunquan Huang, Cong Yu
Summary: This study investigates the influence of cooling on the growth rate of unstable Rossby wave instabilities (RWIs) using linear perturbation analysis. Two different methods are used to model the cooling associated with the energy equation. The results show that the difference in growth rate between adiabatic and isothermal modes becomes more pronounced for discs with smaller sound speed. The growth rate of unstable modes monotonically decreases with shorter cooling time-scale in barotropic discs, but the dependence becomes non-monotonic in non-barotropic discs. The RWIs might even be enhanced in non-barotropic discs during the transition from the adiabatic state to the isothermal state.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
A. S. Tavleev, G. Lipunova, K. L. Malanchev
Summary: This article introduces a new PYTHON code that calculates the vertical structure and stability of accretion discs around compact objects, taking into account radiative and convective energy transport. Analytic formulas for the farthest regions of the hot disc around a stellar-mass object are provided based on more accurate power-law approximations for opacity. The self-consistent value of the irradiation parameter C-irr is calculated for a self-irradiated disc, showing weak dependence on the accretion rate but changes with radius, driven by the conditions in the photosphere and disc opening angle. The extent of the hot zone is determined by the ratio between irradiating and intrinsic flux.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
D. A. Bollimpalli
Summary: In this study, we investigated the influence of the gravitational potential of a rotating star on the orbital motion of particles orbiting the star. We found that the nature of these characteristic frequencies differs based on the geometry of the rotating star.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Mitchell C. Begelman, Philip J. Armitage
Summary: We propose a self-regulation mechanism in which the strength of angular momentum transport in accretion discs threaded by net vertical magnetic field is determined by the magnetorotational instability (MRI). This mechanism reproduces the known scaling of the viscous alpha-parameter, with weak assumptions on the turbulence structure. We also generalize this argument to discs with strong suprathermal toroidal magnetic fields and speculate that tearing modes may be a possible source of enhanced turbulence in elevated discs.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)