Black holes and accretion flows

Chris DoneUniversity of Durham

Aya Kubota Marek Gierlinski Nick Schurch

Matt MiddletonJeanette Gladstone

Strong gravity

• Black holes: extreme spacetime curvature

• Test Einsteins GR - event horizon, last stable orbit…..

• The thing about a black hole, its main distinguishing feature is, its black. And the thing about space, your basic space colour is its black. So how are you supposed to see them? (Red Dwarf)

Rs

Accretion

• Accreting BH: huge X-ray luminosity close to event horizon Rs

• Emission from region of strong spacetime curvature

• Observational constraints on strong gravity if we can understand accretion!

• Appearance of BH should depend only on mass and spin (black holes have no hair!)

• Plus mass accretion rate, giving observed luminosity L

• Maximum luminosity ~LEdd where radiation pressure blows further infalling material away

• Get rid of most mass dependance as accretion flow should scale with L/LEdd

• 104-1010 M: Quasars • 10-1000(?) M: ULX • 3-20 M: Galactic black holes

Black holes

• Huge amounts of data• Timescales

• ms – year (observable!)

• hours – 108 years in quasars • Observational template of

accretion flow as a function of L/LEdd onto ~10 M BH

• Comparison sample of NS: 1.4 M objects

Galactic Binary systems

7 years

• Einstein BH: event horizon and last stable orbit Rlso~3Rs – gravity stronger than Newtonian

• Neutron stars. R~3Rs so gravitational potential for accretion flow the same.

• Look at same L/LEdd for accretion flow – difference reveals presence/absence of surface ie existance of event horizon!

Event horizon

• Differential Keplerian rotation

• Viscosity B: gravity heat

• Thermal emission: L = AT4

• Temperature increases inwards

• GR last stable orbit gives minimum radius Rlso - depends on spin 3 0.5 Rs (a = 0 1)

• For a=0 and L~LEdd Tmax is

• 1 keV (107 K) for 10 M

• 10 eV (105 K) for 108 M

• big black holes luminosity scales with mass but area scales with mass2 so T goes down with mass!

• Maximum spin Tmax is 3x higher

Spectra of accretion flow: disc

Log

Log

f

(

• Pick ONLY ones that look like a disc!

• L/LEdd T4max (Ebisawa et al 1993; Kubota

et al 1999; 2001)

• Constant size scale – last stable orbit!!

• Proportionality constant gives a measure Rlso i.e. spin

• Consistent with low to moderate spin not extreme spin nor extreme versions of higher dimensional gravity - braneworlds (Gregory, Whisker, Beckwith & Done 2004)

Gierlinski & Done 2003

Disc spectra: last stable orbit

• Bewildering variety of spectra from single object

• Underlying pattern

• High L/LEdd: soft spectrum, peaks at kTmax often disc-like, plus tail

• Lower L/LEdd: hard spectrum, peaks at high energies, not like a disc

Gierlinski & Done 2003

But rest are not simple…

• Disc models assumed thermal plasma – not true at low L/LEdd

• Instead: hot, optically thin, geometrically thick inner flow replacing the inner disc (Shapiro et al. 1976; Narayan & Yi 1995)

• Hot electrons Compton upscatter photons from outer cool disc

• Few seed photons, so spectrum is hard

• Jet from large scale height flow

Accretion flows without discs

Log

Log

f

(

• Disc models assumed thermal plasma – not true at low L/LEdd

• Instead: hot, optically thin, geometrically thick inner flow replacing the inner disc (Shapiro et al. 1976; Narayan & Yi 1995)

• Hot electrons Compton upscatter photons from outer cool disc

• Few seed photons, so spectrum is hard

• Jet from large scale height flow

Accretion flows without discs

Log

Log

f

(

• Disc models assumed thermal plasma – not true at low L/LEdd

• Instead: hot, optically thin, geometrically thick inner flow replacing the inner disc (Shapiro et al. 1976; Narayan & Yi 1995)

• Hot electrons Compton upscatter photons from outer cool disc

• Few seed photons, so spectrum is hard

• Jet from large scale height flow collapse of flow=collapse of jet

Accretion flows without discs

Log

Log

f

(

• Disc models assumed thermal plasma – not true at low L/LEdd

• Instead: hot, optically thin, geometrically thick inner flow replacing the inner disc (Shapiro et al. 1976; Narayan & Yi 1995)

• Hot electrons Compton upscatter photons from outer cool disc

• Few seed photons, so spectrum is hard

• Jet from large scale height flow collapse of flow=collapse of jet

Accretion flows without discs

Log

Log

f

(

Qualitative and quantitative models: geometry

Log

Log

f

(

Log

Log

f

(

Hard (low L/LEdd)

Soft (high L/LEdd)

Done & Gierliński 2004

1.53.04.5

Observed GBH spectra• Truncated disc Rlso

qualitative and quantitative• RXTE archive of many GBH • Same spectral evolution

10-3 < L/LEdd < 1Done & Gierliński 2003

1.5

4.5

3.0

6.4-

16)

3-6.4)

1.5

4.5

3.0

6.4-

16)

LS

VHS

HS

US

Hard (low L/LEdd)

Soft (high L/LEdd)

Lh/Ls

1

Scale up to AGN/QSOs• Same accretion flow onto higher mass black hole (?)• Spectral/jet states in AGN with L/LEdd

• Tmax M -1/4 – disc emission in UV, not X-ray• Magorrian-Gebhardt relation gives BH mass!!

Bla

ck h

ole

mas

s

Stellar system mass

103

109

1061012

VHS

HS

US

Hard (low L/LEdd)

Soft (high L/LEdd)

Done & Gierliński 2005

LS

Radio IR Opt UV X

AGN complex environmentL

og

f

10 14 18

RL QSO’s

RQ QSO’s

• Cold absorption from torus along equatorial plane: unified schemes for AGN…BUT

• BHB say AGN not all the same even underneath: L/LEdd

Conclusions• Test GR - X-rays from accreting black holes produced in

regions of strong gravity • Event horizon (compare to NS)

• Last stable orbit (ONLY simple disc spectra) L T4max

• Corrections to GR from proper gravity must be smallish• Accretion flow NOT always simple disc – X-ray tail!

• Models of accretion flow and jet changing with L/LEdd

• Apply to AGN – spectrum and jet and wind from disc will change with L/LEdd – feedback controls galaxy formation in Universe as a whole

• ASTROPHYSICS PHYSICS