Thin Accretion Disk Model(Shakura & Sunyaev 1973; Novikov & Thorne
1973; …)
Thin Accretion Disk Model(Shakura & Sunyaev 1973; Novikov & Thorne
1973; …)
Geometrically thin: H = R (except as L LEdd)Cool gas: cs = vK, p = ρvK
2
Radiatively efficient: Lacc ≡ η Mdot c2 ~ (0.06-0.4) Mdot c2
Optically thick --- blackbody-like radiation
1/ 41/ 4
8
Edd
10 eV10
MkTM
MM
•−
•
⎛ ⎞⎛ ⎞ ⎜ ⎟≈ ⎜ ⎟ ⎜ ⎟⎜ ⎟⎝ ⎠ ⎝ ⎠
Systems With Thin Accretion Disks
Systems With Thin Accretion Disks
Most quasars and luminous AGN
Big Blue Bump in the optical/UV is from the disk
(but detailed spectral fits are not very successful)
Radiatively efficient (Soltan 1982; Elvis et al.
2002; Yu & Tremaine 2002)
BH X-ray binaries in the “high soft state” or
“thermal state” (excellent spectral fit)
Radio loud
Radio quietElvis et al.
(1994)BBB
BBB
Radio Quiet
BBB
Ultra-Dim Galactic NucleiUltra-Dim Galactic NucleiSgr A* exemplifies an old problem:
SMBHs in the nuclei of normal (non-AGN) galaxies are
much too dim
True, the gas supply is less than in a bright AGN
But the gas supply is less by only a few orders of
magnitude, not by >8 orders of magnitude as Sgr A*’s
luminosity suggests
Apart from the ultra-low luminosity, the spectrum also
suggests something other than the usual thin disk
Observations of Sgr A*
Observations of Sgr A*
Sgr A* is extremely dim:
(Baganoff et al. 2001ab; Genzel et al. 2003; Ghez et al. 2003)
Bondi accretion 1041 erg/s
Shape of the spectrum is
completely wrong for thin disk
Thin disk (or surface) with even
10-10 Mε/yr is not allowed
36 9submm Edd
35 10IR Edd
33 11X Edd
~10 erg/s ~ 3 10
~10 erg/s ~ 3 10
~ 2 10 e(
rg/s 10 brighter during flares)
L L
L L
L L
−
−
−
×
×
× <
~
Other Nearby Galactic NucleiOther Nearby
Galactic Nuclei
Most have low luminosities: LLAGN
They lack a Big Blue Bump in their spectra
Observed luminosity is far less than one estimates given the mass supply rate (Fabian & Canizares 1988)
Low observed luminosity unlikely to be due to inclination or obscuration (quite obvious in BHXRBs)
Strongly suggests a different mode of accretion
Ho (2005)
LLAGN
RQ AGN
RL AGNBBB
Energy Equationq+ = q - + qadv
Energy Equationq+ = q - + qadv
Thin Accretion Disk(Shakura & Sunyaev 1973; Novikov & Thorne 1973;…)
Most of the viscous heat energy is radiated
Advection-Dominated Accretion Flow (ADAF)
(Ichimaru 1977; Narayan & Yi 1994, 1995; Abramowicz et al. 1995)
Most of the heat energy is advected with the gas
adv
2rad 0.1
q q q
L M c
− +≈
:
adv
2rad
2adv
0.1
0.1
q q q
L M c
L M c
− + ≈
:
Properties of ADAFs: 1Properties of ADAFs: 1Thin disk to ADAF boundary occurs at
luminosities L ~ 0.01—0.03 LEdd, or
Mdot ~ 0.01—0.03 MdotEdd (for reasonable model parameters: α ~ 0.1)
Location of the boundary is nicely consistent
with the L/LEdd at which LLAGN regime kicks
in (and where BH XRBs switch from the
thermal state to the low hard state)
Boundary Between Thin Disk and ADAF
Boundary Between Thin Disk and ADAF
Boundary can be roughly estimated as a function of luminosity from observations (Yuan & Narayan 2004) Hard to calculate from first principles, but the results are consistent with basic models (e.g., Narayan & Yi 1995)
Yuan & Narayan (2004)
Mdot Regimes: Thin Disk vs ADAF
Mdot Regimes: Thin Disk vs ADAF
Thin disk found in unshaded areas:
bright XRBs, bright AGN, SNe, GRBs
ADAF found in shaded areas:
Radiatively inefficient ADAF (RIAF,
Narayan & Yi 1995): LLAGN, hard state
BHXRB, quiescent XRB, Sgr A*
Radiation-trapped ADAF (slim disk,
Begalman 1978, Abramowicz et al. 1988)
Narayan & Quataert (2005)
(M = 3Mε)
Properties of ADAFs: 2Properties of ADAFs: 2By definition, an ADAF has low radiative efficiencyRoughly, we expect a scaling (Narayan & Yi 1995):
Extreme inefficiency of SgrA* and quiescent nuclei explained, at least qualitatively (Narayan, Yi & Mahadevan 1995; Fabian & Rees 1995; Reynolds et al. 1996; Yi 1996; Di Matteo et al. 2000, 2003; Haiman & Menou 2000;…)
2
ADAF ADAF
crit crit
0.1 ;M MLM M
η• •
• •
⎛ ⎞ ⎛ ⎞⎜ ⎟ ⎜ ⎟≈ ∝⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠
Narayan & Yi (1995)
Esin et al. (1997)
Properties of ADAFs: 3Properties of ADAFs: 3Very hot: Ti ~ 1012 K/r, Te ~ 109-11 K (virial, since ADAF loses very little heat)
Large pressure: cs ~ vK
Geometrically thick: H/R ~ 1
Sub-Keplerian rotation: Ω< ΩK
Optically thin (because of low density)
No Big Blue Bump
Consistent with observations
Yuan et al.
History of Nuclear SMBHsHistory of Nuclear SMBHsBright AGN have thin disks, LLAGN have ADAFs
SMBHs produce most of their luminosity in the
thin disk phase (quasars, bright AGN)
SMBHs spend most of their time (90-99%) in
the ADAF phase (quiescence)
In which phase do SMBHs accrete most of their
mass? Answer: Thin disk (Hopkins et al. 2005)
Properties of ADAFs: IVWinds and Jets
Properties of ADAFs: IVWinds and Jets
Narayan & Yi (1994, Abstract):
… the Bernoulli parameter is positive, implying that advection-dominated flows are susceptible to producing outflows … We suggest that advection-dominated accretion may provide an explanation for … the widespread occurrence of outflows and jets in accreting systems
Strong outflows confirmed in numerous hydro and MHD simulations (Stone et al. 1999; Igumenshchev et al. 1999; Blandford & Begelman 1999; McKinney 2005;…)
Evidence for strong mass loss in Sgr A* (Quataert & Gruzinov 2000; Agol 2000; Bower et al. 2003;…)
There should be a connection between outflows and jets
MHD Jet SimulationsMHD Jet SimulationsNumerical MHD simulations of ADAFs around rotating BHs produce impressive jets/outflows(Koide et al. 2002; de Villiers et al. 2003; McKinney & Gammie 2004; Komissarov 2004; Semenov et al. 2004; McKinney 2005; …)
McKinney (2005)
OUTFLOW
JET
Jet/wind/accretion connection
Jet/wind/accretion connection
Relativistic jet may be inner part of wind or may be from BH
In either case, likely collimated bywind (e.g., Lynden-Bell 2006)
Suggests that a strong wind is needed for a strong jet
If so, strong jets should be associated with ADAFs --- jet-ADAF models (Markoff, Falcke, Yuan et al.)
Jets might also form in thin diskswith radiatively driven winds
Radio Jets in AGN
Radio Jets in AGN
Radiatively inefficient ADAF present in Sgr A* (Narayan et al. 1995, 1998; Yuan et al. 2003, 2004), LINERs (Lasota et al. 1996), FRI sources (Reynolds et al. 1996; Begelman & Celotti 2004), LLAGN (Quataert et al. 2000), BL Lacs(Maraschi & Tavecchio 2003), XBONGs (Yuan & Narayan 2004)
Jet activity/radio emission is expected and is seen
λ = L/LEdd
R’ = 6 cm /B band
Radio-quiet AGN probably have no ADAF, only thin disk (evidence not as strong as in XRBs, Fender et al.) Ho (2002)
Feedback From Jets and Winds
Feedback From Jets and Winds
Relativistic jets are dramatic and very visible
But there is likely to be a lot more energy in the less
collimated coronal wind from an ADAF (McKinney 2005)
This wind is present through most of the life of an
SMBH
Must surely affect galaxy evolution
Feedback: Quasars vs LLAGNFeedback: Quasars vs LLAGNQuasars produce most of their energy output in radiationBut probably only a small fraction of the luminosity couples to the external mediumLLAGN produce most of their energy output in a wind/outflowMechanical wind energy couples 100% with the external mediumIntegrated over the life of an SMBH, which phase dominates feedback?
AGN Feedback History AGN Feedback History If SMBH gains mass ΔMTD in thin disk phase, feedback energy ~ 0.1 ε ΔMTD c2, where ε is probably = 1 (guess)
If SMBH gains mass ΔMADAF (< ΔMTD) in ADAFphase, feedback energy 0.1 ΔMADAF c2
Contributions could be comparably important
ADAF feedback acts through most of the life of an SMBH, whereas TD is episodic
Feedback and ADAF Accretion Feedback and ADAF Accretion
Sgr A* is extremely underluminousbecause of 4 factors, all cooperating together:
Low mass supply: MdotBondi ~ 10-4 MdotEdd
Mass Outflow: MdotBH ~ 10-2.5MdotBondi
Low Rad. eff.: Lacc ~ 10-2 (0.1 MdotBH c2)
Energy feedback: suppresses MdotBondi
itself (Ostriker…)
SummarySummaryBroadly, two distinct kinds of BH accretion
Thin accretion diskVery luminous – bulk of accretion luminosity in the universe
Characterized by blackbody emission: BBB
Probably weak wind no/weak jet (in BHXRBs; in AGN??)
ADAFSMBHs spend most of their time in this state
Do not produce much radiation or accrete much mass
But there could be considerable feedback in this phase
Very strong winds can confine strong jets
Many AGN jets probably associated with ADAFs (e.g., FRI)
Top Related