Transcript transparencies - Rencontres de Moriond

GRAVITY
Studying the supermassive black hole at
the center of the Galaxy
46th Rencontres de Moriond and GPHyS colloquium 2011
Gravitational Waves and Experimental Gravity
Guy Perrin and the GRAVITY consortium
Thursday 25 March 2011
The Galaxy
Milky Way
Diàmeter: 25 kpc
Spiral galaxy with bar
Solar system
The environment of Sgr A*
Sgr A*
10 µas
Mini spiral
Central cluster
(2 disks)
(0.5 pc-12.5’’)
S star cluster
(12-400 mas)
(50’’)
The mass of Sgr A*
6 cm radio continuum emission
4
The VLT, Very Large Telescope
4 european 8 m telescopes at Cerro Paranal in Chili
l/D @ 2 µm = 60 mas (600 a.u. or 0.003 pc)
© Lacombe 2001
Adaptive Optics
A deformable mirror
compensates the
errors of the incident
wavefront
A real-time
calculator optimizes
the correction
A sensor measures residual errors
The corrected
wavefront leads
to a good image
at the
diffraction limit
Absorption toward Sgr A*
is huge
Av=32
Infrared observations are
required
Accurate mass of Sgr A*
(3D orbits: imaging and spectroscopy)
3rd Kepler law:
a3 GMSgrA *

2
T
4 2
MSgr A*= 3.61±0.32 106 MSun
(d = 7.62±0.32 kpc)
Eisenhauer et al. (2005)
The nature of Sgr A*
6
size (Rs(2.8x10 Msun ))
Size in RS
101
103
105
6
2.8x10
BH
3x106 MM
⊙sun
Black hole
-3
S2 orbit
-3
1019
10
>105 yrs
Proper motions
-8
1014
10
Fermion
ball
fermion ball
(17 keV)
(17 keV)
Gas motion
9
10
9
>10 yrs
density
at 0.5"
Stellarstellar
cuspcusp
at 0.5”
>1010 yrs
10-7
density nuclear
Nuclear
starStarcluster
cluster at 0.3 pc
10-5
10-3
Sizesize
in pc
(pc)
density (g cm )
bosonstar
star
102
SgrA* size
and motion
-3
density (Msun pc )
1024
10-1
10-13
The flaring Sgr A*
Genzel et al. (2003)
Flares vs. time
• Central black hole activity ~ once a night
• Minimum period ~ 20 minutes
Genzel et al. (2003)
Possible origin of flares
Flare: matter is heated on a (the
innernmost stable) circular orbit (30
µas if J=0)
Flare period: period of the orbit
Fantastic tool to study general
relativity in the strong field regime.
The hot spot will be used as a test
particle to measure the space time
around Sgr A*.
Eckart et al. A&A 500, 935 (2009)
12
Going beyond boundaries thanks to accurate
spatial information
• Bring the ultimate evidence that Sgr A* is a black hole: the mass is
contained in the Schwarzschild radius.
• Understand the nature of flares.
• Use the black hole as a tool to study general relativity in the strong
field regime
Scale ~ 1 Rs
10 µas
• Study relativistic effects on nearby stars
• Understand the nature of S stars and their distribution
Scale ~ 100 Rs
1 mas
GRAVITY – 4 giant telescope interferometer
(General Relativity viA Vlt InterferomeTrY)
l/B @ 2 µm = 3 mas (30 a.u. or 0.00015 pc)
GRAVITY Consortium
Amorim, Araujo-Hauck, Bartko, Baumeister, Berger, Brandner, Carvas, Cassaing, Chapron,
Choquet, Clénet, Collin, Dodds-Eden, Eckart, Eisenhauer, Fédou, Fischer, Gendron, Genzel,
Gillessen, Gräter, Hamaus, Haubois, Haug, Hippler, Hofmann, Hormuth, Houairi, Ihle, Jocou,
Kellner, Kervella, Klein, Kolmeder, Lacour, Lapeyrère, Laun, Lenzen, Lima, Moratschke,
Moulin, Naranjo, Neumann, Patru, Paumard, Perraut, Perrin, Pfuhl, Rabien, Ramos, Reess,
Rohloff, Rousset, Sevin, Sturm, Straubmeier, Thiel, Vincent, Wiest, Zanker-Smith, Ziegleder,
Ziegler
Principle of the measurements with GRAVITY
Reference source for infrared
adaptive optics
Reference sources for 10 µas
astrometry and 3 mas phase
reference imaging
Imaging of the innermost stellar cluster
(not too difficult)
The central cluster (60 mas) is resolved at a scale of 3 mas = 300 Rg
1 night of observation
Paumard et al. (2005)
Point source response
Raw image
After deconvolution
Imaging of the innermost stellar cluster
(not too difficult)
The central cluster (60 mas) is resolved at a scale of 3 mas = 300 Rg
15 months of observation
Paumard et al. (2005)
(mas)
(mas)
Relativistic precession (assuming Schwarzschild metric)
No-hair theorem test
(very difficult)
Spinning black hole  larger precession
(Lense-Thirring effect) and precession of
the orbital plane (J and Q2)
J
Q2
GRAVITY limit after 1 year
Will (2008)
Wheeler’s no-hair theorem: a black hole
is described by 3 parameters: Mass M,
Spin J, Charge
Quadrupolar moment Q2 = -J2 / M
Interferometric astrometry
Distance between two interferograms:
Reference
star
Dopd = B DS
Sgr A*
DS
Hence:
DS = Dopd / B
With a 5 nm accuracy on Dopd and a
100 m baseline, precision on DS reaches
10 µas.
Dopd =B DS
A 1€ coin on the Moon as seen from
Earth !
0
20
opd
Detecting and constraining the Innersmost Stable
Circular Orbit with astrometry
(very difficult)
Scattering of measured positions
Expected scattering for
a 30 µas orbit
Orbiting flare
The orbit diameter
depends on J
 potential
measurement of J
Fixed flare
Vincent et al. (2010)
Where do we stand now ?
Concept Design Review:
Preliminary Design Review:
Final Design Review:
First tests at Paranal:
December 2007
December 2009
October 2011
2014
Hopefully first results on Sgr A* in 4 years.
Orbites d’étoiles S observées par le VLT autour de
Sgr A*
Sgr A*
Schödel et al. (2002)
Orbites d’étoiles S observées par le VLT autour de
Sgr A*
S2
Sgr A*
Schödel et al. (2002)
Sursaut calculé par Frédéric
Vincent avec GYOTO
(1200 h de calcul)
Inclinaison de l’orbite = 70°
Trou noir statique.
Dernière orbite circulaire stable.
Distance observateur = 50 Rs
25