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

Spectral Modeling of Accretion Disks around Compact Stars

2009 ◽  
Author(s):  
Thorsten Nagel ◽  
Stephan Hartmann ◽  
Thomas Rauch ◽  
Klaus Werner ◽  
Ivan Hubeny ◽  
...  
Keyword(s):  
Accretion Disks ◽  
Compact Stars ◽  
Spectral Modeling

scholarly journals Kinematic Dynamo in Turbulent Circumstellar Disks

1993 ◽  
Vol 157 ◽  
pp. 203-207
Author(s):  
T. Stepinski
Keyword(s):  
Magnetic Fields ◽  
Normal Mode ◽  
Accretion Disk ◽  
Accretion Disks ◽  
Adiabatic Approximation ◽  
Circumstellar Disks ◽  
Compact Stars ◽  
Kinematic Dynamo ◽  
Protoplanetary Nebulae ◽  
Galactic Dynamos

Many circumstellar disks associated with objects ranging from protoplanetary nebulae to accretion disks around compact stars allow for the generation of magnetic fields by an αω dynamo. We have applied kinematic dynamo formalism to geometrically thin accretion disks. We calculate, in the framework of an adiabatic approximation, the normal mode solutions for dynamos operating in disks around compact stars. We then describe the criteria for a viable dynamo in protoplanetary nebulae, and discuss the particular features that make accretion disk dynamos different from planetary, stellar, and galactic dynamos.

scholarly journals Magnetohydrodynamic Origin of Jets from Accretion Disks

1999 ◽  
Vol 194 ◽  
pp. 208-218 ◽  
Author(s):  
R.V.E. Lovelace ◽  
G.V. Ustyugova ◽  
A.V. Koldoba
Keyword(s):  
Accretion Disks ◽  
Mass Flux ◽  
Compact Stars ◽  
Young Stellar Objects ◽  
Region Of Origin ◽  
Stellar Objects ◽  
New Developments ◽  
Poynting Flux ◽  
Radio Jets ◽  
Astrophysical Objects

A review is made of recent magnetohydrodynamic (MHD) theory and simulations of origin of jets from accretion disks. Many compact astrophysical objects emit powerful, highly-collimated, oppositely directed jets. Included are the extra galactic radio jets of active galaxies and quasars, and old compact stars in binaries, and emission line jets in young stellar objects. It is widely thought that these different jets arise from rotating, conducting accretion disks threaded by an ordered magnetic field. The twisting of the B field by the rotation of the disk drives the jets by magnetically extracting matter, angular momentum, and energy from the accretion disk. Two main regimes have been discussed theoretically, hydromagnetic winds which have a significant mass flux, and Poynting flux jets where the mass flux is negligible. Over the past several years, exciting new developments on models of jets have come from progress in MHD simulations which now allow the study of the origin -the acceleration and collimation - of jets from accretion disks. Simulation studies in the hydromagnetic wind regime indicate that the outflows are accelerated close to their region of origin whereas the collimation occurs at much larger distances.

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.

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

Quantum 20/20

2019 ◽  
Author(s):  
Ian R. Kenyon
Keyword(s):  
Quantum Mechanics ◽  
Hall Effect ◽  
Particle Physics ◽  
Quantum Spin ◽  
Lessons Learned ◽  
Compact Stars ◽  
Einstein Condensation ◽  
Local Conservation ◽  
Variable Theory ◽  
Quantum Gauge Theory

This text reviews fundametals and incorporates key themes of quantum physics. One theme contrasts boson condensation and fermion exclusivity. Bose–Einstein condensation is basic to superconductivity, superfluidity and gaseous BEC. Fermion exclusivity leads to compact stars and to atomic structure, and thence to the band structure of metals and semiconductors with applications in material science, modern optics and electronics. A second theme is that a wavefunction at a point, and in particular its phase is unique (ignoring a global phase change). If there are symmetries, conservation laws follow and quantum states which are eigenfunctions of the conserved quantities. By contrast with no particular symmetry topological effects occur such as the Bohm–Aharonov effect: also stable vortex formation in superfluids, superconductors and BEC, all these having quantized circulation of some sort. The quantum Hall effect and quantum spin Hall effect are ab initio topological. A third theme is entanglement: a feature that distinguishes the quantum world from the classical world. This property led Einstein, Podolsky and Rosen to the view that quantum mechanics is an incomplete physical theory. Bell proposed the way that any underlying local hidden variable theory could be, and was experimentally rejected. Powerful tools in quantum optics, including near-term secure communications, rely on entanglement. It was exploited in the the measurement of CP violation in the decay of beauty mesons. A fourth theme is the limitations on measurement precision set by quantum mechanics. These can be circumvented by quantum non-demolition techniques and by squeezing phase space so that the uncertainty is moved to a variable conjugate to that being measured. The boundaries of precision are explored in the measurement of g-2 for the electron, and in the detection of gravitational waves by LIGO; the latter achievement has opened a new window on the Universe. The fifth and last theme is quantum field theory. This is based on local conservation of charges. It reaches its most impressive form in the quantum gauge theories of the strong, electromagnetic and weak interactions, culminating in the discovery of the Higgs. Where particle physics has particles condensed matter has a galaxy of pseudoparticles that exist only in matter and are always in some sense special to particular states of matter. Emergent phenomena in matter are successfully modelled and analysed using quasiparticles and quantum theory. Lessons learned in that way on spontaneous symmetry breaking in superconductivity were the key to constructing a consistent quantum gauge theory of electroweak processes in particle physics.

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

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
Sign in / Sign up

Export Citation Format

Share Document