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)