Radiatively Radiatively Inefficient Inefficient

Accretion FlowsAccretion Flows

Roman Shcherbakov,Roman Shcherbakov,

28 November, 200728 November, 2007

Radiative efficiencyRadiative efficiency

Innermost Stable Circular Orbit (ISCO)Gas radiates away a lot of its grav. energy

0.06-0.42 efficiency (function of BH spin)

ADAF

Gas accretes onto the source, butdoes not radiate due to (1) low density(2) low electron temperature (3) large optical depth

efficiency (function of gas density)

Radiatively InefficientAccretion Flows (RIAFs)

Possible RIAF Possible RIAF configurationsconfigurationsSpherical (Bondi) accretion

– dimensionless angular momentum

for a typical AGN

for Sgr A*

The only realistic pattern: every astrophysical system has

large angular momentum

+ outflows

Spherical accretion Spherical accretion (Bondi, 1952)(Bondi, 1952)

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

–

for

Br

u

gr

Sr

u=cS at sonic radius rS, subsonic flow at r>rS, supersonic flow at r>rSSuch a solution is (1)Smooth(2)Has maximum accretion rate

Physical

Efficiency

Not only AGNs, but also Gamma Ray Bursts

and protoplanetary disks

Thick disk Thick disk accretionaccretion

Advection-Dominated Accretion Flow(Narayan, Yi 1995)

Adiabatic Inflow-Outflow Solution(Blandford, Begelman 1999)

Hawley,Balbus 2002

ADAF luminosityADAF luminosity

Large opticaldepth ADAF(ULX sources)

Nara

yan, M

ahadevan, Q

uata

ert

ast

ro-p

h/9

80

31

41

ADAF/ADIOS/CDAFADAF/ADIOS/CDAFAdvection-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)

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

Phenomenological inclusion of outflows“The binding energy of a gram of gas at a few gravitational radii drives off100 kg of gas from gravitational radii” – Blandford

Accounts for convective instability of ADAF, but full 3-D analysis is not doable analytically

SpectrumSpectrum

Jet-ADAF model for Sgr Jet-ADAF model for Sgr A*A*

Yuan,Markoff, Falcke 2002

Spectral statesSpectral states

Hard –X-Rays

Soft –UV, IR

Narayan, Mahadevan, Quataert astro-ph/9803141http://www.mpe.mpg.de/~amueller/lexdt_a02.html

Haw

ley,

Balb

us,

“The D

yn

am

ical Str

uct

ure

of

Non

radia

tive B

lack

Hole

Acc

reti

on F

low

s” 2

00

2, A

pJ, 5

73,

738

Haw

ley,

Balb

us,

“The D

yn

am

ical Str

uct

ure

of

Non

radia

tive B

lack

Hole

Acc

reti

on F

low

s” 2

00

2, A

pJ, 5

73,

738

Results of Numerical Results of Numerical SimulationsSimulations

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

Density

Entropy

Time variabilityTime variability

At r=4rg

Densi

tyTem

pera

ture

ConclusionsConclusions

• 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?