Black Hole Accretion

Theoretical Limits And Observational Implications

Black Hole Accretion

Theoretical Limits And Observational Implications

Dominikus Heinzeller

Institute for Theoretical AstrophysicsCenter for Astronomy Heidelberg

Albert-Ueberle-Str. 2, 69120 Heidelberg

dh@ita.uni-heidelberg.de

Dominikus Heinzeller

Institute for Theoretical AstrophysicsCenter for Astronomy Heidelberg

Albert-Ueberle-Str. 2, 69120 Heidelberg

dh@ita.uni-heidelberg.de Credit: Michael Owen, John Blondin

slide 2D. Heinzeller: Black Hole Accretion; IAU 2006, 08/23/2006

Outline

1. Black hole accretion and the Eddington limit

2. Spectral energy distribution of super-Eddington flows

3. Conclusions

In collaboration with W.J. Duschl, S. Mineshige, K. Ohsuga

Supported by:

Outline

Black holeaccretion

SED of super-Eddington flows

Conclusionsand outlook

slide 3D. Heinzeller: Black Hole Accretion; IAU 2006, 08/23/2006

Classical Eddington limit

• global upper limit for the luminosity of a star• spherical approximation often used in accretion discs:

rF

gF

• spherical symmetry

• homogeneous

• isotropic radiation

• no relativistic effects

• Thomson scattering

• no gas pressure

effT

r g E

4 + = 0 =

cGMF F L

38 8disc

erg1.2 10 2.6 10

s aM M

L m M m mM

Outline

Black holeaccretion

SED of super-Eddington flows

Conclusionsand outlook

slide 4D. Heinzeller: Black Hole Accretion; IAU 2006, 08/23/2006

Contradictions

• cosmology: SMBHs in the early universeaccretion scenarios require super-Eddington accretion

• observation of super-Eddington luminosities: ULXs– sub-Eddington IMBHs?

too hot accretion disc problem– super-Eddington stellar mass BHs?

Current and previous work:• modification of global classical Eddington limit• local deviations

– leaky discs (Begelman 2002)– critical accretion discs (Fukue 2000, 2004)

E10L L

Outline

Black holeaccretion

SED of super-Eddington flows

Conclusionsand outlook

slide 5D. Heinzeller: Black Hole Accretion; IAU 2006, 08/23/2006

Local Eddington limit in discs

• local Eddington limit for radial and vertical direction

• thin -discs (Shakura & Sunjaev 1973)• slim discs: advection (Abramowicz et al. 1980/1988)• Thomson scattering and interpolated opacities

(Gail, priv comm.)

• spherical symmetry

• homogeneous

• isotropic radiation

• no relativistic effects

• Thomson scattering

• no gas pressure

effT

??

rF

gF gFcF

r,oF r,iF

Outline

Black holeaccretion

SED of super-Eddington flows

Conclusionsand outlook

slide 6D. Heinzeller: Black Hole Accretion; IAU 2006, 08/23/2006

Local Eddington limit in discs

• radial upper limit on vertical upper limit• • unimportant

for high (advection),otherwise crucial

• inner boundary?(here: torque-free)

• slim disc, :

while

M

Vertical Eddington limit

BH

7i

10

8.86 10 cm

=0.1

M M

s

crit E/M M

i/s s

1 2critM s

critM

3crit E/ 1 10M M

E/ 1 20L L

/ 1h s

Outline

Black holeaccretion

SED of super-Eddington flows

Conclusionsand outlook

slide 7D. Heinzeller: Black Hole Accretion; IAU 2006, 08/23/2006

SED of super-Eddington flows

• based on 2D RHD simulations (Ohsuga et al. 2005)– high accretion rates – energy transport via radiation and advection– consideration for photon trapping

• observer at inclination • parallel line of sight calculation of radiative

transfer– relativistic

effects– electron

scattering– -dependent

ff-absorption

0 /2

3E BH( 10 , 10 )M M M M

Outline

Black holeaccretion

SED of super-Eddington flows

Conclusionsand outlook

slide 8D. Heinzeller: Black Hole Accretion; IAU 2006, 08/23/2006

SED of super-Eddington flows

[erg/s]L

[eV]E

BlackbodyBlackbodytemperaturetemperaturefit to peak:fit to peak:

6

6

5

T(0)=

1.5 10 K

T( /4)

1.2 10 K

( /2)

9.4 10 K

T

Outline

Black holeaccretion

SED of super-Eddington flows

Conclusionsand outlook

slide 9D. Heinzeller: Black Hole Accretion; IAU 2006, 08/23/2006

SED of super-Eddington flows

mild relativistic beaming mild relativistic beaming

Outline

Black holeaccretion

SED of super-Eddington flows

Conclusionsand outlook

Blackbodytemperaturefit to peak:

6

6

5

T(0)=

1.5 10 K

T( /4)

1.2 10 K

( /2)

9.4 10 K

T

slide 10D. Heinzeller: Black Hole Accretion; IAU 2006, 08/23/2006

Conclusions

Black hole accretion:• classical Eddington-limit not applicable in

discs– depends on disc model– varies with distance from central object– inner disc region/boundary decisive

• bottle-neck in inner disc region• super-Eddington accretion and luminosities

Spectral energy distribution:• modelling of disc and its environment

necessary for interpretation of spectra• mild relativistic beaming

– increased photon number for small – enhanced average photon energy– high temperatures

Influence onBH growth?

Outflows, jets?

Evidencefor IMBH?

NGC 4261Credit:R.M. Elowitz

Outline

Black holeaccretion

SED of super-Eddington flows

Conclusionsand outlook