scholarly journals Shocks in the low angular momentum accretion flow

2015 ◽  
Vol 600 ◽  
pp. 012012 ◽  
Author(s):  
Petra Suková ◽  
Agnieszka Janiuk
Keyword(s):  
Angular Momentum ◽  
Accretion Flow

scholarly journals Magnetohydrodynamic Turbulence in Accretion Discs: Towards More Realistic Models

1997 ◽  
Vol 163 ◽  
pp. 210-214
Author(s):  
Ulf Torkelsson ◽  
Axel Brandenburg ◽  
Åke Nordlund ◽  
Robert F. Stein
Keyword(s):  
Angular Momentum ◽  
Boundary Conditions ◽  
Accretion Disc ◽  
Quantitative Change ◽  
Accretion Discs ◽  
Momentum Transport ◽  
Magnetohydrodynamic Turbulence ◽  
Accretion Flow ◽  
Angular Momentum Transport ◽  
Main Effects

AbstractThe shearing box has rapidly become the accepted way to investigate turbulence in Keplerian shear flows. In this paper we discuss to what extent and in which way the outcome of the shearing box is affected by the adopted boundary conditions, and how the shearing box can be modified to capture more of the physics of an accretion disc. The original shearing box model is too symmetric to generate a net accretion flow, but the symmetry can be broken by including the main effects of the cylindrical geometry of the real disc. However the quantitative change in the resulting angular momentum transport is small.

scholarly journals The surprisingly small impact of magnetic fields on the inner accretion flow of Sagittarius A* fueled by stellar winds

2019 ◽  
Vol 492 (3) ◽  
pp. 3272-3293 ◽  
Author(s):  
S M Ressler ◽  
E Quataert ◽  
J M Stone
Keyword(s):  
Angular Momentum ◽  
Magnetic Fields ◽  
Event Horizon ◽  
Initial Conditions ◽  
Rotational Instability ◽  
Stellar Winds ◽  
Accretion Flow ◽  
Sagittarius A ◽  
Mhd Simulations ◽  
Sgr A

ABSTRACT We study the flow structure in 3D magnetohydrodynamic (MHD) simulations of accretion on to Sagittarius A* via the magnetized winds of the orbiting Wolf–Rayet stars. These simulations cover over 3 orders of magnitude in radius to reach ≈300 gravitational radii, with only one poorly constrained parameter (the magnetic field in the stellar winds). Even for winds with relatively weak magnetic fields (e.g. plasma β ∼ 106), flux freezing/compression in the inflowing gas amplifies the field to β ∼ few well before it reaches the event horizon. Overall, the dynamics, accretion rate, and spherically averaged flow profiles (e.g. density, velocity) in our MHD simulations are remarkably similar to analogous hydrodynamic simulations. We attribute this to the broad distribution of angular momentum provided by the stellar winds, which sources accretion even absent much angular momentum transport. We find that the magneto-rotational instability is not important because of (i) strong magnetic fields that are amplified by flux freezing/compression, and (ii) the rapid inflow/outflow times of the gas and inefficient radiative cooling preclude circularization. The primary effect of magnetic fields is that they drive a polar outflow that is absent in hydrodynamics. The dynamical state of the accretion flow found in our simulations is unlike the rotationally supported tori used as initial conditions in horizon scale simulations, which could have implications for models being used to interpret Event Horizon Telescope and GRAVITY observations of Sgr A*.

ACCRETION PROBLEM IN A KERR BLACK HOLE GEOMETRY VIEWED AS FLOWS IN CONVERGING–DIVERGING DUCTS

2010 ◽  
Vol 19 (13) ◽  
pp. 2059-2069
Author(s):  
K. CHAKRABARTI ◽  
M. M. MAJUMDAR ◽  
SANDIP K. CHAKRABARTI
Keyword(s):  
Black Hole ◽  
Angular Momentum ◽  
Mach Number ◽  
Cross Sections ◽  
Kerr Black Hole ◽  
Flat Space ◽  
Accretion Flow ◽  
Black Hole Accretion ◽  
Hole Geometry ◽  
Hole Accretion

Accretion flow on a horizon is supersonic, no matter what the flow angular momentum or the spin of the black hole is. This means that a black hole accretion can always be viewed as a flow in a flat space–time through one or more convergent–divergent ducts. In this paper, we study how the area of cross-sections must vary in order that the flow has the same properties in both systems. We show that the accretion flow experiencing a shock is equivalent to having two ducts connected back-to-back, both with a neck where the flow becomes supersonic. We study the pressure and Mach number variations for corotating, contrarotating flows and flows around a black hole with evolving spin.

scholarly journals Disk Structure and Evolution Around the Neutron Star in Be/X-Ray Binaries

2004 ◽  
Vol 194 ◽  
pp. 230-230
Author(s):  
Kimitake Hayasaki ◽  
Atsuo T. Okazaki
Keyword(s):  
Angular Momentum ◽  
Neutron Star ◽  
Orbital Plane ◽  
X Ray ◽  
Accretion Flow ◽  
Disk Structure ◽  
Disk Size ◽  
Short Period ◽  
Stage Process ◽  
X Ray Binaries

We investigate the accretion flow around the neutron star in Be/X-ray binaries, using a 3D SPH code and the data imported from simulations by Okazaki et al. (2002) and Okazaki & Hayasaki (2004) for both a coplanar system and a misaligned system in which the Bo-star disk is inclined from the binary orbital plane by 30 degrees, with a short period (Porb = 24.3 days) and moderate eccentricity (e = 0.34). We find that a non-steady accretion disk is formed around the neutron star in the misaligned case as well as in the coplanar case. The disk size in the misaligned system is significantly larger because of its higher angular momentum than that in the coplanar system. We also find that the disk also evolves via a two-stage process, which consists of the initial developing stage and the latar developed stage.

scholarly journals Hot Accretion onto Black Holes with Outflow

2018 ◽  
Vol 168 ◽  
pp. 04005
Author(s):  
Myeong-Gu Park ◽  
Du-Hwan Han
Keyword(s):  
Black Holes ◽  
Angular Momentum ◽  
Accretion Rate ◽  
Host Galaxies ◽  
Accretion Flow ◽  
Mass Accretion Rate ◽  
Viscosity Parameter ◽  
Growth History ◽  
History Of ◽  
Flow Study

Classic Bondi accretion flow can be generalized to rotating viscous accretion flow. Study of hot accretion flow onto black holes show that its physical charateristics change from Bondi-like for small gas angular momentum to disk-like for Keperian gas angular momentum. Especially, the mass accretion rate divided by the Bondi accretion rate is proportional to the viscosity parameter alpha and inversely proportional to the gas angular momentum divided by the Keplerian angular momentum at the Bondi radius for gas angular momentum comparable to the Keplerian value. The possible presence of outflow will increase the mass inflow rate at the Bondi radius but decrease the mass accretion rate across the black hole horizon by many orders of magnitude. This implies that the growth history of supermassive black holes and their coevolution with host galaxies will be dramatically changed when the accreted gas has angular momentum or develops an outflow.

scholarly journals Outflow from Hot Accretion Flows

2012 ◽  
Vol 8 (S290) ◽  
pp. 86-89
Author(s):  
Feng Yuan ◽  
Defu Bu ◽  
Maochun Wu
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Large Scale ◽  
Mhd Flows ◽  
Accretion Flow ◽  
Accretion Flows ◽  
Outward Motion ◽  
Convection Dominated ◽  
The Magnetic Field ◽  
Open Magnetic Field

AbstractNumerical simulations of hot accretion flows have shown that the mass accretion rate decreases with decreasing radius. Two models have been proposed to explain this result. In the adiabatic inflow-outflow solution (ADIOS), it is thought to be due to the loss of gas in outflows. In the convection-dominated accretion flow (CDAF) model, it is explained as because that the gas is locked in convective eddies. In this paper we use hydrodynamical (HD) and magnetohydrodynamical (MHD) simulations to investigate which one is physical. We calculate and compare various properties of inflow (gas with an inward velocity) and outflow (gas with an outward velocity). Systematic and significant differences are found. For example, for HD flows, the temperature of outflow is higher than inflow; while for MHD flows, the specific angular momentum of outflow is much higher than inflow. We have also analyzed the convective stability of MHD accretion flow and found that they are stable. These results suggest that systematic inward and outward motion must exist, i.e., the ADIOS model is favored. The different properties of inflow and outflow also suggest that the mechanisms of producing outflow in HD and MHD flows are buoyancy associated with the convection and the centrifugal force associated with the angular momentum transport mediated by the magnetic field, respectively. The latter mechanism is similar to the Blandford & Payne mechanism but no large-scale open magnetic field is required here. Possible observational applications are briefly discussed.

scholarly journals Star Formation and Bipolar Flows

1987 ◽  
Vol 115 ◽  
pp. 336-340
Author(s):  
Ralph E. Pudritz
Keyword(s):  
Angular Momentum ◽  
Star Formation ◽  
Mechanical Energy ◽  
Rotational Energy ◽  
Molecular Gas ◽  
Rotating Disks ◽  
Bipolar Outflows ◽  
Molecular Outflows ◽  
Accretion Flow ◽  
Flow Through

Observations of molecular outflows from regions of star formation show that they cannot be radiatively driven ((Ṁv)mol ≥ 102 – 103 (L./c)). The thrust observed to be associated with the smaller scale ionized outflows is also incapable of driving the molecular gas ((Ṁv)ion ≃ (L./c), Persson et al 1984). The results may be explained if bipolar flows are hydromagnetic winds from molecular disks around protostars. These winds carry off disk rotational energy (observed as the mechanical energy of the outflows) and angular momentum (observed when rotation of the outflowing gas is found), which drives an accretion flow through it and onto the protostellar core (Pudritz 1985, Pudritz and Norman 1983, 1986). Therefore star formation and bipolar outflows occur simultaneously when magnetized, rotating disks are the source of activity.

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