Measuring the SPIN of Black Holes

Andy FabianInstitute of Astronomy

University of Cambridge

Astrophysical Black Holes have only MASS and SPIN (like elementary particles, except BH

can have any mass )

BLACK HOLES

Karl Schwarzschild Roy Kerr

MASS can be measured over wide range of radii

but SPIN requires measuring properties at small radii

What effects are characteristic of small radii around a Black Hole?

Strong Gravity Effects

• Gravitational redshift

• Gravitational light bending

• Dragging of inertial frames in Kerr metric (ISCO depends on BH spin)

GPS GR=45microsec/day(or ~10km/day)

GRAVITATIONAL LIGHT BENDING

Information from spectra and variability

• X-ray ‘reflection’ gives important clues in the spectrum

• Variability timescales and spectral changes show different spectral components

Reflection from photoionized matter(Ross & Fabian 93, 05)

Also see Young+, Nayakshin+, Ballantyne+, Rozanska+, Dumont+

Schwarzschild

Kerr

Fabian+89, Laor 90… Dovciak+04;

Beckwith+Done05

Suzaku

Strength and behaviour of line implies GRAVITATIONAL LIGHT BENDING

MCG-6-30-15

Red wing due to large gravitational redshiftimplying BH rapidly

spinning

Lockman Hole800 ks XMM-Newton observation

Hasinger

Lockman Hole800 ks XMM-Newton observation

Hasinger

Streblyanskaya et al 2004

Assumption: measurements of rISCO determine (or constrain) a

Radius of innermost stable circular orbit-ISCO

Probing Black Hole Spin

Light bending model in Kerr spacetime

Miniutti et al 03; Miniutti & Fabian 04; earlier work by Martocchia, Matt+

see also Tsuebsuwong, Malzac+06

Armitage & Reynolds

SPIN also affects radiative efficiency of accretion, η

2

2

cML

McE

2

2

2

42.0

057.0

005.0

McE

McE

McE

Nuclear fusion

Black Hole Accretion

211105 McE TNT

Max spin BH accretion

Accretion makes massive black holes

2

1)1( cz

Soltan 82

Mean redshift Radiative efficiency

Light Mass density in BH

η > 0.1Observations

Much of the radiation originates within 6Rg

Accretion makes massive black holes

2

1)1( cz

Soltan 82

Mean redshift Radiative efficiency

Light Mass density in BH

η > 0.1Observations

Most Massive BH are rapidly spinning