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Radiatively Inefficient Accretion Flows

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Radiatively Inefficient Accretion Flows

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Radiatively Inefficient Accretion Flows

Roman Shcherbakov,

28 November, 2007

Gas accretes onto the source, but

does not radiate due to

(1) low density

(2) low electron temperature (3) large optical depth

efficiency

(function of gas density)

Innermost Stable Circular Orbit (ISCO)

Radiatively Inefficient

Accretion Flows (RIAFs)

Gas radiates away a lot of its grav. energy

0.06-0.42 efficiency (function of BH spin)

ADAF

The only realistic pattern:

every astrophysical system has

large angular momentum

for a typical AGN

for Sgr A*

Spherical (Bondi) accretion

+ outflows

– dimensionless angular momentum

radius of influence of BH, 1pc for 10^8MSun

–

for

- u=cS at sonic radius rS, subsonic flow at r>rS, supersonic flow at r>rS
- Such a solution is
- Smooth
- Has maximum accretion rate

Efficiency

Physical

Thick disk accretion

Adiabatic Inflow-Outflow Solution

(Blandford, Begelman 1999)

Hawley,

Balbus 2002

Advection-Dominated Accretion Flow

(Narayan, Yi 1995)

Not only AGNs, but also Gamma Ray Bursts

and protoplanetary disks

Large optical

depth ADAF

(ULX sources)

Narayan, Mahadevan, Quataert astro-ph/9803141

Advection-Dominated Accretion Flow (Narayan, Yi 1995)

- Needed to fit the observations
- Too low electron temperature Te<<Ti near the black hole
- Too Low gas density near the black hole
- Too small magnetic field in that region
- ADAF is convectively unstable and does not include diffusion

Adiabatic Inflow-Outflow Solution (Blandford, Begelman 1999)

ADAF with outflows (Yuan 2001)

Phenomenological inclusion of outflows

“Thebinding energy of a gram of gas at a fewgravitational radii drives off

100 kg of gas from gravitational radii” – Blandford

Convection-Dominated Accretion Flows (Narayan, Igumenshchev, & Abramowicz 2000)

Accounts for convective instability of ADAF,

but full 3-D analysis is not doable analytically

Yuan,Markoff, Falcke 2002

Soft –

UV, IR

Hard –

X-Rays

Narayan, Mahadevan, Quataert astro-ph/9803141

http://www.mpe.mpg.de/~amueller/lexdt_a02.html

Hawley, Balbus, “The Dynamical Structure of

Nonradiative Black Hole Accretion Flows” 2002, ApJ, 573, 738

Hawley, Balbus, “The Dynamical Structure of

Nonradiative Black Hole Accretion Flows” 2002, ApJ, 573, 738

Density

Entropy

Hawley, Balbus & Stone, 2001 ApJ, 554, L49

Temperature

At r=4rg

Density

- Studies are controversial
- Realistic accretion pattern is likely to be very complicated
- Numerical simulations are preferable to analytical methods
- Most effects are not yet included, small resolution
- MHD instead of plasma calculations
- Developed in the last 30 years, will we get the ultimate
- answer within the next 30 years?