Black Hole Event HorizonBlack Hole Event Horizon

A Black Hole has a truly

unique property: it possesses

an Event Horizon

A “virtual” surface

One-way membrane ---

matter/energy can fall in, but

nothing gets out, not even

light

Singularity

Event Horizon

A Black Hole is Amazingly Simple

A Black Hole is Amazingly Simple

Mass: M

Spin: a* (J=a*GM2/c)

Charge: QEven though it is a macroscopic object, a BH is as simple as an elementary particle!

Can We Test These Features?

Can We Test These Features?

Confirm that astrophysical BHs actually do have Event Horizons

Measure the two fundamental parameters of BHs Mass (relatively easy) Spin (much harder)

Ramesh Narayan, Jeff McClintock

Do Black Hole Candidates Have Event

Horizons?

Do Black Hole Candidates Have Event

Horizons?

Are Black Hole Candidates really

BHs?

Can we find independent evidence

that our BH candidates actually

possess Event Horizons

X-ray BinariesX-ray Binaries

Image credit: Robert Hynes (2002)

The IdeaThe Idea Find BH X-ray Binaries

in which the accretion flow radiates very little

Objects with surfaces (NSs) will then be much brighter than objects with event horizons (BHs)

Look for a huge difference in luminosity

Narayan, Garcia & McClintock (1997)

Large difference in luminosity between BHs and NSs is dramatically verified (Narayan, Garcia & McClintock; Garcia et al. 2001; McClintock et al. 2003; …)

Black Holes are really black!! Event Horizon

Black Hole SpinBlack Hole Spin

The material from which a BH is formed

almost always has angular momentum

Also, accretion adds angular

momentum

So we expect astrophysical BHs to be

spinning: J = a*GM2/c, 0 a* 1

Can we measure a*?

The Basic IdeaThe Basic Idea

Measure radius of hole by estimating area of the bright inner disk

(Zhang et al. 1997; Shafee et al. 2006; McClintock et al. 2006)

Black Hole ParametersBlack Hole Parameters

X-ray Binary Mass (M) a*

4U1543-47 7.4—11.4 0.75—0.85

LMC X-3 5.9—9.2 < 0.3

GRO J1655-40 6.0—6.6 0.65—0.75

GRS 1915+105

10--18 0.98—1