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)
Article
Astronomy & Astrophysics
Xiaochen Sun, Xue-Ning Bai
Summary: This study investigates the impact of MRI turbulence in hot accretion flows on particle diffusion and stochastic acceleration, revealing patterns in spatial diffusion coefficients and momentum diffusion coefficients for particles with different gyro-radii. The results suggest that multiple factors contribute to stochastic acceleration/deceleration, influenced by intermittency in the MRI turbulence. The study also discusses the potential for accelerating PeV cosmic rays in hot accretion flows around supermassive black holes.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Martijn J. C. Wilhelm, Simon Portegies Zwart
Summary: Recent studies have revealed that 'Peter Pan discs' phenomenon can only occur around M dwarf stars, not around stars of higher mass. The lifetime of primordial discs depends on the host star's mass, with stars less than 0.6 solar masses being able to retain the discs for about 50 Myr.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Andrei Gruzinov
Summary: The study investigates the rate of subsonic wind accretion and demonstrates that it is independent of wind velocity and equal to the spherical Bondi rate when the adiabatic index is 5/3. A highly accurate numerical calculation is also provided to confirm this finding.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Sohan Ghodla, J. J. Eldridge
Summary: Recently, it has been found that a photon-trapping surface is not sufficient for unimpeded superEddington (SE) accretion. In this study, we derive a condition that allows sustained and unimpeded SE accretion in optically thick slim accretion discs around neutron stars (NSs) and black holes (BHs). Our findings suggest that sustained SE accretion is possible in slim discs around BHs with an Eddington fraction m≥1.5(e/0.1)^(3/5) regardless of their spin, and in slim discs around NSs with e≤0.03. However, the presence of a surface magnetic field in NSs can affect the efficiency and change the condition to m≥0.013e^(-19/31).
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Cristiano Longarini, Philip J. Armitage, Giuseppe Lodato, Daniel J. Price, Simone Ceppi
Summary: Young protostellar discs can undergo short-wavelength fragmentation of solid components, forming Earth-mass solid cores during the early stages of stellar evolution. The ability of spiral structures to concentrate solids increases with cooling time and decreases with the Stokes number. Our results suggest that the best conditions for planet formation occur near the end of the self-gravitating phase, with a long cooling time and a Stokes number close to unity.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Hongping Deng, Gordon Ogilvie
Summary: The non-linear behavior of low-viscosity warped discs is examined using direct 3D hydrodynamical simulations. It is found that a non-linear bending-wave theory, in which fluid columns undergo affine transformations, is valid for moderate non-linearity but suffers from severe numerical dissipation in a smoothed particle hydrodynamics (SPH) method. The study also reveals that a stable non-linear state does not exist in a thin disc when the outer tilt angle exceeds a certain value.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
C. P. Dullemond, C. N. Kimmig, J. J. Zanazzi
Summary: This paper examines and analyzes the evolution equations of warped discs under high and low viscosity conditions. It derives a unified set of equations using the warped shearing box framework and discusses how these results can be interpreted.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Gavin A. L. Coleman, Thomas J. Haworth
Summary: This study explores the evolution and dispersal of protoplanetary discs under the influence of internal and external photoevaporation and varying degrees of viscous transport. It identifies five distinct dispersal pathways and shows that the relative impact of internal and external winds, as well as the clearing pathway, vary with different stellar/disc/radiation properties. The study highlights the importance of considering both internal and external winds in understanding protoplanetary disc evolution.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
James E. Owen, Noumahn Altaf
Summary: The study demonstrates that externally photoevaporating discs produce a smooth transition from rotationally supported Keplerian discs to photoevaporative driven outflows. The penetration of ultraviolet photons predominantly determines the radius of the transition, with the strength of viscosity playing a minor role. By studying the entrainment of dust particles, rapid changes in dust properties in the transition region are observed.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Juan C. Vallejo, Ana Ines Gomez de Castro
Summary: Protoplanetary discs are complex dynamic systems with flared profiles that may favor the formation of ring-like structures, but these features seem to be short-lived and further enhancements are still needed for better matching all the features seen in real systems.
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
J. Fukue
Summary: The paragraph presents radiation hydrodynamical equations including Compton scattering, which are applicable in the subrelativistic regime and with low fluid velocities. Several basic concepts and phenomena related to radiation hydrodynamics under Compton scattering are briefly discussed.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
R. Yamamoto, J. Fukue
Summary: The study focuses on general relativistic radiatively-driven spherical winds, considering basic equations for relativistic radiation hydrodynamics under the moment formalism. Results show different types of critical points under various parameter conditions, with the most suitable type being saddle points near black holes.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
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)
