Post on 29-Dec-2015
Probing the close environment of the supermassive black hole at the center
of the galaxy with GRAVITY
Probing Strong Gravity Prague, February 18, 2010
Perrin
Probing the close environment of the supermassive black hole at the center
of the galaxy with GRAVITY
Probing Strong Gravity Prague, February 18, 2010
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, Straubmeier,
Thiel, Vincent, Wiest, Zanker-Smith, Ziegleder, Ziegler
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Mini spiral(50’’)
S star cluster(12-400 mas)
Circumnuclear disk(120’’)
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2-disk centralcluster
(0.5 pc-12.5’’)
The environment of Sgr A* Sgr A*
10 µas
Orbits of stars around Sgr A*
Schödel et al. (2002)
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Orbits of stars around Sgr A*
Schödel et al. (2002)
S2
Two ways of measuring strong GRAVITY effects around Sgr A*
1. Studying the closest star orbits inside the central 60 mas
Need to resolve star cluster.
Scale ~ 100 Rg = 1 mas resolution.
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(mas) (mas)
Relativistic precession in Schwarzschild metric
Sgr A* blinking
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Genzel et al. (2003)
Two ways of measuring strong GRAVITY effects around Sgr A*
2. Using flaring regions as test particles.
Measure flare motion.Scale ~ 1 Rg = 10 µas
accuracyTime scale = 10 min
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Genzel et al. (2003) Hot spot orbiting the ISCO or a more distant orbit.
Eckart et al. A&A 500, 935 (2009)
Sgr A* is quite dark
Long wavelengths are well suited.Stars are bright in the near-infrared (orbits) and instruments sensitive enough to allow for short exposures (flares).
How to get to the 1 mas resolution and 10 µas accuracy in
the near-infrared ?
One of Prague famous astronomers,
Tycho Brahe, found the solution:
use a large instrument
Measurement accuracy scales as the
reciprocal of the size of the instrument.
Use the 4 VLT in interferometric mode
~ 140 m
Resolution: 3 mas @ 2.2 µm(K band)
Build GRAVITY !(General Relativity viA Vlt InterferomeTrY)
Interferometric imaging in the near-
infrared worksAltair
Monnier et al. 2007
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Cep
Zhao et al. 2008
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Betelgeuse
Haubois et al. 2009
Mira
Perrin et al. in prep
Cyg
Lacour et al. 2009
Imaging the closest stars with GRAVITY
One-night observation image:
Paumard et al. (2005)
mas mas
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Point Spread Function Dirty 6-star image After deconvolution
mas mas mas
Imaging the closest stars with GRAVITY
Orbits after 15 months of observation:
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Paumard et al. (2005)
mas mas
1 mas = 100 Rg
Schwarzschild advance of pericenter is detected
Lens-Thirring and Quadrupole Precession
Testing the no-hair theorem
Orbital plane precession (precession of the angular momentum vector around the spin of the black hole)
Will (2008)
Wheeler’s “black holes have no hair” theorem: a BH is fully characterized by only three parameters: Mass M, Spin J, Electric chargeIn particular Quadrupole Q2 = -J2 / M
1 year orbit, e=0.9
Measurement of frame dragging precession may be feasible after a few years for orbits in the radial range between 0.2 mpc and 1 mpc (5 and 25 mas)Merritt et al. (2009)
Referencestar Sgr A*
The measured distance between the two interferograms is:
opd = B.S
Hence:
S = opd/B
A 5 nm accuracy on opd with a 100 m baseline yields a 10 µas accuracy on S.
S
opd0
opd = B.S
Narrow angle interferometric astrometry
Performance analysis:• errors from atmosphere, baseline, noise, pupil position, etc …• 23 µas per baseline• 13 µas with 6 baselines
Muterspaugh et al. (2006): “… the 20μas level has been demonstrated …”
110 m and 87 m baselines40 cm telescopes
The Palomar Testbed Interferometer did it !
See Frédéric Vincent’s talk
Measuring the last stable orbit
Newtonprimary GR image
totalimage
secondary GR image
Paumard et al. (2005)
Reference sources for GRAVITY near Sgr A*
2”
K ~ 9.6
Sgr A*
K ~ 15 - 18
Reference source for adaptive optics
Reference sources - IRS 16 - for interferometry (imaging and astrometry)
GRAVITY is in the design …
Adaptive Optics Wavefront Sensor
Metrology Laser Injection
Fringe Tracking Spectrometer
Science Spectrometer
IO Beam combiner
… and prototyping phase
Fibered delay line
4-telescope integrated optics beam combiner
Laser metrology system
Metrology test on VLT secondary mirror at Paranal
Where we are standing and where we are going
Preliminary Design Review took place in december 2009
Final Design Review is scheduled for June 2011
First tests at Paranal : 2014
Hopefully first results on Sgr A* in 5 years from now.