shadows of black holes - idpasc · 2016. 6. 29. · in fact, the bhs lense each other !multiple...
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Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Shadows of black holes
Pedro V. P. da Cunha1, 2
1 Departamento de Física da Universidade de Aveiro and CIDMA2 IST, Universidade de Lisboa
in collaboration with: C. Herdeiro, E. Radu, H. Rúnarsson
PhysRevLett.115.211102
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
What is a BH?
Source: Interstellar
Black Holes (BHs) are predicted in General Relativity (GR).
They are compact states from which light cannot escape.
The event horizon is the no turning point.
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Sagittarius A*
Gillessen et al.
Center of the Milky Way→ evidence for a supermassive BH.
Stars orbit an extremely massive object: 4× 106M�.
This massive object is dubbed Sagittarius A*.
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Kerr Black Hole
M
~J
Kerr space-time→ describes a rotating BH in vacuum.
It is the most standard BH in astrophysics.
The BH is uniquely determined by M and J = Ma.
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
What is a BH shadow?
Optical perception of a BH→ silhouette over background light.
This dark silhouette is called a shadow.
It is the fingerprint of the BH event horizon and its geometry.
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Shadow of a BH merger
arXiv:1410.7775 [gr-qc]
This is how a BH binary would look like!
Here we have two large shadows.
In fact, the BHs lense each other→ multiple shadows!
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Backwards ray-tracing
Backwards ray-tracing
Numerical integration of light rays yields the shadow.
It is more efficient to evolve the rays backwards in time.
This numerical procedure is called backwards ray-tracing.
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Backwards ray-tracing
Celestial sphere
Reference: arXiv:1410.7775 [gr-qc]
The BH and the observer are placed inside a colored sphere.
BH is in the center of the sphere.
The observer is in the equatorial plane.
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Backwards ray-tracing
Shadows of Kerr BHs
The Kerr shadow is not symmetric due to rotation.
Inside the Einstein ring→ inverted copy of the celestial sphere.
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Backwards ray-tracing
Shadows of Kerr BHs
Adapted K.Thorne.
The edge of the shadow has a recurrence structure.
Photons encircle the black hole an increasing number of times.
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Event Horizon Telescope
Source: Doleman et al.
Event Horizon Telescope→ international array of telescopes.
It aims to probe Sgr A* and obtain the first images of a shadow.
New observational templates are required!
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Introduction to “hair”
Source: Cinema 4D
Uniqueness theorems→ BHs are determined only by M and J.
This lead to the no-hair conjecture.
“Hair” is a metaphor for extra parameters (no Gauss law).
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Scalar fields
Source: Cinema 4D
Scalar fields→ simplest descriptions of matter.
One may search for BH solutions coupled with scalar fields.
However, solutions with “good” matter are very hard to find...
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Kerr BHs with scalar hair
Einstein-Klein-Gordon system
S =
∫d4x√−g[
R16πG
−∇νφ∇νφ∗ − µ2φ∗φ
].
Einstein’s gravity minimally coupled to a complex scalar field φ.
A stationary BH solution exists, in equilibrium with φ.Herdeiro & Radu: PhysRevLett.112.221101
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Shadows of Hairy BHs
Kerr BH with scalar hair Kerr BH (same M, J)
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Shadows of Hairy BHs
0
0.5
1
0.6 0.7 0.8 0.9 1
Mµ
w/(mµ)
Boson Stars (q=1)
extremal KBHsSH
m=1
q=0.97
q=0.85
q=1
q=0
Kerr black holes
The shadows of hairy BHs can be very distinct from Kerr’s.
These shadows are smaller!
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Shadows of Hairy BHs
0
0.5
1
0.6 0.7 0.8 0.9 1
Mµ
w/(mµ)
Boson Stars (q=1)
extremal KBHsSH
m=1
q=0.97
q=0.85
q=1
q=0
Kerr black holes
The shadows of hairy BHs can be very distinct from Kerr’s.
These shadows are smaller!
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Shadows of Hairy BHs
0
0.5
1
0.6 0.7 0.8 0.9 1
Mµ
w/(mµ)
Boson Stars (q=1)
extremal KBHsSH
m=1
q=0.97
q=0.85
q=1
q=0
Kerr black holes
The shadows of hairy BHs can be very distinct from Kerr’s.
These shadows are smaller!
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Shadows of Hairy BHs
0
0.5
1
0.6 0.7 0.8 0.9 1
Mµ
w/(mµ)
Boson Stars (q=1)
extremal KBHsSH
m=1
q=0.97
q=0.85
q=1
q=0
Kerr black holes
The shadows of hairy BHs can be very distinct from Kerr’s.
These shadows are smaller!
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Shadows of Hairy BHs
0
0.5
1
0.6 0.7 0.8 0.9 1
Mµ
w/(mµ)
Boson Stars (q=1)
extremal KBHsSH
m=1
q=0.97
q=0.85
q=1
q=0
Kerr black holes
The shadows of hairy BHs can be very distinct from Kerr’s.
These shadows are smaller!
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Shadows of Hairy BHs
0
0.5
1
0.6 0.7 0.8 0.9 1
Mµ
w/(mµ)
Boson Stars (q=1)
extremal KBHsSH
m=1
q=0.97
q=0.85
q=1
q=0
Kerr black holes
The shadows of hairy BHs can be very distinct from Kerr’s.
These shadows are smaller!
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Shadows of Hairy BHs
0
0.5
1
0.6 0.7 0.8 0.9 1
Mµ
w/(mµ)
Boson Stars (q=1)
extremal KBHsSH
m=1
q=0.97
q=0.85
q=1
q=0
Kerr black holes
The shadows of hairy BHs can be very distinct from Kerr’s.
These shadows are smaller!
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Shadows of Hairy BHs
0
0.5
1
0.6 0.7 0.8 0.9 1
Mµ
w/(mµ)
Boson Stars (q=1)
extremal KBHsSH
m=1
q=0.97
q=0.85
q=1
q=0
Kerr black holes
The shadows of hairy BHs can be very distinct from Kerr’s.
These shadows are smaller!
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Shadows of Hairy BHs
0
0.5
1
0.6 0.7 0.8 0.9 1
Mµ
w/(mµ)
Boson Stars (q=1)
extremal KBHsSH
m=1
q=0.97
q=0.85
q=1
q=0
Kerr black holes
The shadows of hairy BHs can be very distinct from Kerr’s.
These shadows are smaller!
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Shadows of Hairy BHs
Kerr BH with scalar hair Kerr BH (same M, J)
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Shadows of Hairy BHs
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Shadows of Hairy BHs
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Shadows of Hairy BHs
One can try a different pattern just for fun!
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Computational calculations
Source: Sun Microsystems
Previous image: 4000× 6599 pixels.
Amounts to ∼26 million photon orbits!
1/2 day computation in Blafis super-computer (Aveiro).
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
The road ahead..
The future work:
build observational templates for the Event Horizon Telescope.
study shadows in detail for different latitude angles.
analyse shadows of BHs with other types of hair.
Kerr Black Hole Shadows Hairy Black Holes Shadows of Kerr Black Holes with scalar hair
Acknowledgements
Work is supported by the FCT IDPASC Portugal grand No.PD/BD/114071/2015 and by the Calouste GulbenkianFoundation.
Computations were performed at the Blafis cluster, in AveiroUniversity, and at the Laboratory for Advanced Computing,University of Coimbra.
@Gr v
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