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TABLE: A short summary of the basic properties of accretion discs
based on a lecture by Kristen Menou (November 2008, Nordita, Stockholm, Sweden)
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Type
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In proto-planetary systems |
Around white dwarfs
(WD) in cataclysmic binaries
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In black hole (BH)
or neutron star (NS) binaries |
In quasars
and other AGN |
In gamma ray burst
(GRB) sources |
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Accretor |
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Images
click the image |
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Basic physics |
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The central part of a dense molecular cloud collapses to a proto-star surrounded by a proto-planetary accretion disc. Self gravity and sedimentation trigger the formation of planets. Bipolar outflows ("slow" jets) often emerge from proto-planetary discs.
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U Gem is the prototype of a dwarf novae system, i.e. a close stellar binary, with "primary" being a WD with accretion disc. The disc's brightness in the visible light increases 100-fold every ~120 days and returns to the original level after a ~week, due to (mainly) a
limit-cycle instability. | |
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X-ray binaries (XRB) consist a mass loosing main-sequence "secondary" star and accreting BH or NS. Among XRBs, the soft X-ray transients (with BH or NS) show quasi-periodic outbursts. Most of the BH XRBs exhibit "fast" jets, and for this reason are called microquasars. | |
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AGN are supermassive BH at centers of galaxies. Accretion produces radiative power that often outshines the host galaxy. A large torus of
gas and dust partially obscures the accretion disc. "Fast" (almost speed of light) jets emerge from many AGNs. | |
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GRBs are the most energetic explosions in the universe. Models of GRBs invoke a black hole (M~3Msun) accreting matter at highly
super-Eddington rates. The huge power of gamma-rays is possibly due to an extraction of the BH rotational energy (the Blandford- Znajek mechanism). | |
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Angular momentum transport |
Radial: in the inner disc region and at the surface, where the disc is sufficiently ionised (by X-rays, cosmic rays and collisions), via MRI induced turbulence; in the dead zone via gravitational instability
Vertical: via outflows and/or torque exerted by large scale magnetic fields. |
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Local: in the high state via MRI induced turbulent viscosity;
Global: direct dissipation by tidal spirals when the incoming supersonic flow shocks on the accretion disc |
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Local: MRI drives a turbulent viscosity which also produces shear stresses;
Global: spiral shocks? |
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Inner disc: viscous friction (MRI);
Outer disc: unclear, possibly by global disturbances in the gravitational field (gravito-turbulence) |
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Inner disc: MRI induced turbulent viscosity (in the optically thick mid-plane a very large neutrino viscosity could shut off MRI);
Outer disc: (> 140 RG) uncertain |
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Cooling |
Black body radiation, convection, collisions |
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Thin/slim disc: advection, black body radiation;
Adaf: advection, bremsstrahlung, Compton scattering |
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Thick disc (corona): bremsstrahlung, Compton scattering;
Thin disc: black body radiation |
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Inner disc: neutrino cooled;
Outer disc: advection cooled
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Size
Rin-Rout
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1011 - 1015 cm
10-2 - 200 AU
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109 - 1010 cm
10-4 - 10-3 AU |
106 - 1011 cm
10-7 - 10-2 AU |
106 - 1011 cm x [M/Msun]
10 - 106 RG |
105 - 10? cm x [M/Msun]
6 - 10? RG |
midplane
Temperature
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103 - 101 K |
105 - 103 K |
107 - 103 K |
105 - 102 K |
1010 - 109 K |
Luminosity
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L << LEdd |
L << LEdd |
L << LEdd
L ~ LEdd |
L < LEdd
L > LEdd, L >> LEdd |
L >> LEdd |
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Theoretical models |
Mostly thin discs, thick discs (early epochs), layered discs (with a magnetically inactive 'dead zone' in the mid-plane region) |
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Thin discs (truncated and with funnel/column accretion if the WD is magnetised) |
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Thin discs, slim discs, adafs |
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Thick discs (corona), slim discs |
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Thick discs, thin discs, hyper-accretion, ndaf |
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References |
Hartmann (1998)
Alexander (2008) |
Frank, King & Raine (2002)
Warner (2003) |
Frank, King & Raine (2002)
Remillard & McClintock (2006) |
Krolik (1998)
on-line compilation |
Popham, Woosley & Fryer (1999)
Di Matteo, Perna & Narayan (2002) |
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