Approximate Killing Vectors for Computing Spin in ...

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Jul 13, 2007 - Corotating BBH AKVs. Ω0 φ1. In addition to expected. “spin AKV,” we find. 2 more AKVs. No spin! 0. 0.5. 1. 1.5 radians. 0. 20. 40. 60. 80.
Approximate Killing Vectors for Computing Spin in Black-Hole Initial Data and Evolutions Gregory B. Cook Wake Forest University Bernard F. Whiting University of Florida July 13, 2007

Measuring the Spin of a Black Hole • Spin is only rigorously defined at spatial/null infinity. • Must use quasi-local definition: e.g. Brown & York[2] or Ashtekar & Krishnan[1] I √ 2 1 i j Kij ξ s hd x S=− 8π BH   ξi CK ξi =  ξi

AKV

– Greg Cook – (WFU Physics)

˜ ij ⇒ conformal Killing vector of hij : Killing vector of h : Approximate Killing vector of hij

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Approximate Killing Vectors Killing Transport on S 2[3] Diξj = ij L DiL = − 21 2Rij ξj • Equations assume KV exists! • Solution is “path dependent” • Solution violates equations • ξ i 6= ij Dj v

– Greg Cook – (WFU Physics)

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Approximate Killing Vectors Killing Transport on S 2[3] Diξj = ij L DiL = − 21 2Rij ξj

New AKV Method ξ i = ij Dj v+Did Diξj = ij L + Sij +hij Λ

• Equations assume KV exists!

• Find solutions that minimize S ij !

• Solution is “path dependent”

• ξ i = ij Dj v by construction

• Solution violates equations

• L = 12 ij Diξ j by construction

• ξ i 6= ij Dj v

– Greg Cook – (WFU Physics)

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New Approximate Killing Vectors • Minimize Sij S ij = (DiDj v)(DiDj v) − 12 (Dk Dk v)2 ~ 2 = (Div)(Div) = const. subject to constraint that |ξ| L ≡ Sij S ij + 12 2RΘ(Dk v)(Dk v)



δL = 0 δv



ξ i ≡ ij Dj υ

DiDiv + 2L = 0   1 i2 i 2 D DiL − (1 − Θ) 2 (D R)Div − RL = 0

– Greg Cook – (WFU Physics)

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Corotating BBH “Spin AKVs” -6

-5⋅10

CKV KT AKV Θ

-5

1.5⋅10

-6

-4⋅10 -4

-5

10

-3⋅10

-5

Θ



ij

-6

10 10

-6

-6

10

-2⋅10

-7

10

-6

5⋅10

0

0 0

– Greg Cook – (WFU Physics)

0.025 0.05 0.075

0.025

0.1

0.05

-6

-10

mΩ0

0.075

0.1

0

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Corotating BBH AKVs In addition to expected “spin AKV,” we find 2 more AKVs. No spin!

– Greg Cook – (WFU Physics)

φ1 Ω0

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Corotating BBH AKVs In addition to expected “spin AKV,” we find 2 more AKVs. No spin!

φ1 Ω0

80 60

1

40

φ1 φ2

0.5

20

∆φ(radians)

0

degrees

radians

1.5

0

-5

10 -6 5⋅10 0 -6 -5⋅10 0

– Greg Cook – (WFU Physics)

0.025

0.05

mΩ0

0.075

0.1

5

Corotating BBH AKVs z 1 2

Corotating

-6

-5⋅10

-8

Θ

-4⋅10

-8

-2⋅10

-6

-2.5⋅10

0 0.025

0 0 – Greg Cook – (WFU Physics)

0.025

0.05

0.05

mΩ0

0.075

0.1 6

Corotating BBH AKVs z 1 2

Corotating

-6

-5⋅10

-8

Θ

-4⋅10

-8

-2⋅10

-6

-2.5⋅10

0 0.025

0 0 – Greg Cook – (WFU Physics)

0.025

0.05

0.05

mΩ0

0.075

0.1 6

radians

1.5 1

φ1 φ2- π/2

0.5

1.5

80

1

60

0.5

40

0

20 0.0172

0.01722

0

∆φ(radians)

degrees

Corotating BBH AKVs

0

-5

10 -6 5⋅10 0 -6 -5⋅10 0

Large sep. – Greg Cook – (WFU Physics)

0.025

0.05

mΩ0

Ω0

0.075

0.1

Dominant approx. φ1 symmetry axis in green

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radians

1.5 1

φ1 φ2- π/2

0.5

1.5

80

1

60

0.5

40

0

20 0.0172

0.01722

0

∆φ(radians)

degrees

Corotating BBH AKVs

0

-5

10 -6 5⋅10 0 -6 -5⋅10 0

Small sep. – Greg Cook – (WFU Physics)

0.025

0.05

mΩ0

Ω0

0.075

0.1

Dominant approx. symmetry axis in green

φ1

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Non-Spinning BBH AKVs 1.5

radians

1

60 40

0.5

degrees

φ1 φ2- π/2

80

20

z 1 2

0

Non-Spinning

0

-6

-5⋅10

0.025

0.05

MΩ0

0.075

0.1

-7

Θ

-4⋅10

0

-2⋅10

-6

-2.5⋅10

-7

0 0.025

0 0

0.025

– Greg Cook – (WFU Physics)

0.05

0.05

mΩ0

0.075

0.1

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Summary • New method determines best AKV: smallest Sij S ij : ξ i = ij Dj v. • Computed spin essentially the same as from Killing Transport for corotation & non-spinning equal-mass cases. Differences may be more significant when higher spin rates or greater BH distortion are considered. • Only one AKV solution yields spin. Other AKV solutions provide new diagnostic tool for exploring horizon geometry of distorted BHs. • Algorithm for “conformal spheres” implemented and tested. Algorithm for general S 2 nearly finished. – Greg Cook – (WFU Physics)

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References [1] A. Ashtekar and B. Krishnan. Dynamical horizons and their properties. Phys. Rev. D, 68:104030/1–25, 2003. 1 [2] J. D. Brown and J. W. York, Jr. Quasilocal energy and conserved charges derived from the gravitational action. Phys. Rev. D, 47:1407–1419, 1993. 1 [3] O. Dreyer, B. Krishnan, D. Shoemaker, and E. Schnetter. Introduction to isolated horizons in numerical relativity. Phys. Rev. D, 67:024018/1–14, Jan. 2003. 2

– Greg Cook – (WFU Physics)

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