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## PowerPoint Slideshow about 'Radiatively Inefficient Accretion Flows' - nuwa

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Radiative efficiency

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*

Possible RIAF configurationsSpherical (Bondi) accretion

+ outflows

– dimensionless angular momentum

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

–

for

Spherical accretion (Bondi, 1952)- 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

ADAF/ADIOS/CDAF

Advection-Dominated Accretion Flow (Narayan, Yi 1995)

- Needed to fit the observations
- Too low electron temperature Te<
- 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

Jet-ADAF model for Sgr A*

Yuan,Markoff, Falcke 2002

Spectral states

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

Conclusions

- 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?

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