Accretion Discs in AGN, Viscosity and Structure of Accretion Disks

2001 ◽  
Vol 1 ◽  
pp. 53-61
Author(s):  
J.-M. Hure ◽  
D. Richard
Keyword(s):  
Accretion Disks ◽  
Accretion Discs

The Accretion Discs and Bipolar Jets in Orion KL

2001 ◽  
Vol 205 ◽  
pp. 258-259 ◽  
Author(s):  
L. I. Matveyenko ◽  
P. J. Diamond ◽  
D. A. Graham
Keyword(s):  
Fine Structure ◽  
Star Formation ◽  
Accretion Disks ◽  
Surrounding Medium ◽  
Active Regions ◽  
Accretion Discs ◽  
Bipolar Outflows ◽  
Maser Emission

The fine structure of active regions in Orion KL has been studied. It is shown that accretion disks and bipolar outflows accompany star formation. The accretion disks are divided into protoplanetary rings. The H2O super maser emission is associated with the rings and bipolar outflows. The surrounding medium (VLSR=7.74 km/s) amplifies the emission within the maser window by more than two orders of magnitude.

Saturation mechanism and generated viscosity in gravito-turbulent accretion disks

2020 ◽  
Vol 640 ◽  
pp. A53
Author(s):  
L. Löhnert ◽  
S. Krätschmer ◽  
A. G. Peeters
Keyword(s):  
Growth Rate ◽  
Numerical Simulations ◽  
Accretion Disks ◽  
Gravitational Instability ◽  
Turbulent Viscosity ◽  
Radial Distance ◽  
Maximum Growth ◽  
Wave Number ◽  
Radiative Cooling ◽  
Mixing Length

Here, we address the turbulent dynamics of the gravitational instability in accretion disks, retaining both radiative cooling and irradiation. Due to radiative cooling, the disk is unstable for all values of the Toomre parameter, and an accurate estimate of the maximum growth rate is derived analytically. A detailed study of the turbulent spectra shows a rapid decay with an azimuthal wave number stronger than ky−3, whereas the spectrum is more broad in the radial direction and shows a scaling in the range kx−3 to kx−2. The radial component of the radial velocity profile consists of a superposition of shocks of different heights, and is similar to that found in Burgers’ turbulence. Assuming saturation occurs through nonlinear wave steepening leading to shock formation, we developed a mixing-length model in which the typical length scale is related to the average radial distance between shocks. Furthermore, since the numerical simulations show that linear drive is necessary in order to sustain turbulence, we used the growth rate of the most unstable mode to estimate the typical timescale. The mixing-length model that was obtained agrees well with numerical simulations. The model gives an analytic expression for the turbulent viscosity as a function of the Toomre parameter and cooling time. It predicts that relevant values of α = 10−3 can be obtained in disks that have a Toomre parameter as high as Q ≈ 10.

Iron Fluorescence from within the Innermost Stable Orbit of Black Hole Accretion Disks

1997 ◽  
Vol 488 (1) ◽  
pp. 109-118 ◽  
Author(s):  
Christopher S. Reynolds ◽  
Mitchell C. Begelman
Keyword(s):  
Black Hole ◽  
Accretion Disks ◽  
Stable Orbit ◽  
Black Hole Accretion ◽  
Hole Accretion

A New Instability of Accretion Disks around Magnetic Compact Stars

1998 ◽  
Vol 503 (1) ◽  
pp. 350-360 ◽  
Author(s):  
Mario Vietri ◽  
Luigi Stella
Keyword(s):  
Accretion Disks ◽  
Compact Stars

scholarly journals The Physics of Accretion Discs, Winds and Jets in Tidal Disruption Events

2021 ◽  
Vol 217 (1) ◽  
Author(s):  
Jane Lixin Dai ◽  
Giuseppe Lodato ◽  
Roseanne Cheng
Keyword(s):  
Accretion Discs ◽  
Tidal Disruption

scholarly journals Dynamical structure of highly eccentric discs with applications to tidal disruption events

2020 ◽  
Vol 500 (3) ◽  
pp. 4110-4125
Author(s):  
Elliot M Lynch ◽  
Gordon I Ogilvie
Keyword(s):  
Thermal Instability ◽  
Vertical Structure ◽  
Scale Height ◽  
Accretion Discs ◽  
Radiative Cooling ◽  
Dynamical Structure ◽  
Tidal Disruption ◽  
The Subject ◽  
Stable Solutions ◽  
Physical Quantities

ABSTRACT Whether tidal disruption events circularize or accrete directly as highly eccentric discs is the subject of current research and appears to depend sensitively on the disc thermodynamics. One aspect of this problem that has not received much attention is that a highly eccentric disc must have a strong, non-hydrostatic variation of the disc scale height around each orbit. As a complement to numerical simulations carried out by other groups, we investigate the dynamical structure of TDE discs using the non-linear theory of eccentric accretion discs. In particular, we study the variation of physical quantities around each elliptical orbit, taking into account the dynamical vertical structure, as well as viscous dissipation and radiative cooling. The solutions include a structure similar to the nozzle-like structure seen in simulations. We find evidence for the existence of the thermal instability in highly eccentric discs dominated by radiation pressure. For thermally stable solutions many of our models indicate a failure of the α-prescription for turbulent stresses. We discuss the consequences of our results for the structure of eccentric TDE discs.

scholarly journals Emission from Magnetized Accretion Disks around Young Stars

2017 ◽  
Vol 849 (2) ◽  
pp. 136 ◽  
Author(s):  
C. Tapia ◽  
S. Lizano
Keyword(s):  
Accretion Disks ◽  
Young Stars

scholarly journals Gaseous Disks in the Nuclei of Elliptical Galaxies

1997 ◽  
Vol 163 ◽  
pp. 620-625 ◽  
Author(s):  
H. Ford ◽  
Z. Tsvetanov ◽  
L. Ferrarese ◽  
G. Kriss ◽  
W. Jaffe ◽  
...  
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Angular Momentum ◽  
Accretion Disks ◽  
Large Scale ◽  
Elliptical Galaxies ◽  
Central Mass ◽  
Massive Black Holes ◽  
Radio Jets

AbstractHST images have led to the discovery that small (r ~ 1″ r ~ 100 – 200 pc), well-defined, gaseous disks are common in the nuclei of elliptical galaxies. Measurements of rotational velocities in the disks provide a means to measure the central mass and search for massive black holes in the parent galaxies. The minor axes of these disks are closely aligned with the directions of the large–scale radio jets, suggesting that it is angular momentum of the disk rather than that of the black hole that determines the direction of the radio jets. Because the disks are directly observable, we can study the disks themselves, and investigate important questions which cannot be directly addressed with observations of the smaller and unresolved central accretion disks. In this paper we summarize what has been learned to date in this rapidly unfolding new field.

Sign in / Sign up

Export Citation Format

Share Document