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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 1 3 10 5 10 10 6 2.8x10 BH 3x106 MM ⊙sun Black hole 10 S2 orbit -3 density (Msun pc ) -3 bosonstar star 2 SgrA* size and motion 10-3 19 10 >105 yrs Proper motions -8 14 10 10 Fermion ball fermion ball (17 keV) (17 keV) 109 9 >10 yrs 10-7 Gas motion -13 density at 0.5" Stellarstellar cuspcusp at 0.5” >1010 yrs density nuclear Nuclear starStarcluster cluster at 0.3 pc 10-5 10-3 Sizesize in pc (pc) density (g cm ) 24 10 10-1 10 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