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by James Moran Harvard-Smithsonian Center for Astrophysics University of Barcelona, October 5, 2012 Dinnertime for Sgr A* (The Black Hole in the Center of Our Galaxy)
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Summary of Talk The mass of the black hole in the Center of the Galaxy (Sgr A*) is about 4 x 10 6 solar masses. The accretion rate is about 10 -8 solar masses per year. The polarization is LCP at all wavelengths from 1 mm to 30 cm. (new) The angular diameter of the radio emission from Sgr A* is about 37 microarcseconds at 1.3 mm wavelength. A object of earth mass is approaching the Galactic Center and could increase the accretion rate significantly starting in mid-2013. (new) VLBI observations of M87 and 1924-293 have also been made at 1.3 mm. (new) Event Horizon Telescope (EHT) under development
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Submillimeter Valley, Mauna Kea, HI
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SMA in Intermediate Configuration About 0.5 arcsec resolution at 1 mm
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The Galactic Center on Three Size Scales 1. Circumnuclear (molecular) Disk (CND) and Minispiral (ionized streamers) 120 arcs / 5 pc Zhao, Blundell, Downes, Schuster, Marrone 2. Black hole accretion envelope (100 R s ) 1 mas / 0.3 micro pc Marrone, Munoz, Zhao, Rao 3. SgrA* radio source 37 microarcseconds / 0.01 microparsec Doeleman et al.
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Nine Field Mosaic Image of Circumnuclear Disk in Galactic Center CN H 2 CO SiO SMA Data Sergio Martin Ruiz 3 arcmin field 3 arcs resolution 1.3 mm wavelength
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230 GHz345 GHz 690 GHz Polarization Images at Various Wavelengths from the SMA
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2005 SMA Measurements of Faraday Rotation in Sgr A* Important: SLOPE of polarization angle ~ constant in time at 230 GHz
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Accretion Rate and Faraday Rotation RM = 8.1 x 10 5 n e B dl Assumptions equipartition density power law inner radius cutoff of Faraday screen (,t) = 0 (t) + 2 RM(t) Accretion rate = 10 –9 –10 –7 M Sun /yr RM = –5.1 x 10 5 rad/m 2
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Polarization at Three Frequencies Simultaneously
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Circular Polarization of Sgr A* (red) Stokes I (blue) Stokes V Fractional Circular Polarization vs. Frequency Left handed CP at all frequencies measured!!
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Faraday Conversion in Sgr A* GHz 230 22 1.4 =1 R s 6 80 1600 =1 (diameter) mas 0.06 0.8 16 Range of = 1 surface between 1.4 and 230 GHz: ~350 (based on R =1 ~ -1.1 ) Faraday conversion phase shift = 10 9 L B 4 3 = /2 (optimum) B = magnetic field in Gauss L = length in pc = wavelength in m mode direction in ultrarelativistic plasma mode direction input signal = 1 surface BH
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Some Scales in the Galactic Center
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Simulation of the infrared observations of the stars orbiting the Galactic Center by the Genzel Group
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T = 15.2 years R = 0.12 arcseconds = 17 light hours M = 4 million x the mass of the Sun Density > 10 17 solar masses/pc 3 What is the Central Mass Around Which These Stars Are Orbiting?
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Very faint source still detectible at most astronomical observing bands –SED measurements span 10 decades in frequency L SgrA* ~ 300 L Sun ~ 10 –9 Eddington limit Genzel et al. 2004 X-Ray Radio Submm Near IR IR flare (Hornstein et al. 2007)
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Black Hole “image” Dominated by GR The black hole “shadow” (Bardeen 1973; Falcke, Agol, Melia 2000; Johannsen and Psaltis 2010) Measuring the shadow gives Mass. (Johannsen, Psaltis et al. 2012) Maximally spinning BH Free fall envelope D shadow = 9/2 * R sch Non-spinning BH Rotating accretion envelope D shadow = sqrt(27) * R sch
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Observations of Cygnus A with the Jodrell Bank Intensity Interferometer Square of visibility 125 MHz Jennison and Das Gupta 1952; see also Sullivan
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Cygnus A with Cambridge 1-mile Telescope at 1.4 GHz Ryle, Elsmore, and Neville, Nature, 205, 1259, 1965 3 telescopes 20 arcsec resolution
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Cygnus A with Cambridge 5 km Interferometer at 5 GHz Hargrave and Ryle, MNRAS, 166, 305, 1974 16 element E-W Array, 3 arcsec resolution
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The Synchrotron Emission from Cygnus A Imaged with the VLA at 6 cm Wavelength
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1.3 mm Observations of Sgr A* 4630km VLBI program led by a large consortium led by Shep Doeleman, MIT/Haystack 4030km 908km
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U-V Tracks
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Gaussian and Torus Fit to Visibility Data Gammie et al. 14 Rsch ( as) Doeleman et al. 2008; Fish et al. 2011
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Seeing Through the Scattering OBS deviates from scattering for cm INT SCAT for mm INT
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Sgr A*’s View of the EHT IRAM SPole GLT - Greenland
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Progression to an Image Doeleman et al., “The Event Horizon Telescope,” Astro2010: The Astronomy and Astrophysics Decadal Survey, Science White Papers, no. 68 GR Model station station
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Animation of Accretion Object Discovered by Genzel Group, 2012
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at 5 GHz (insert) and 43 GHz Right ascension offset (mas) VLBA image at 43 GHz by Hada, et al., Nature, 2011
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Beam: 0.43x0.21 mas 0.2mas = 0.016pc = 60R s 1mas/yr = 0.25c VLBA Movie of M87 at 43 GHz (7 mm) (Craig Walker et al. 2008) 6.6 x 10 9 Solar Mass BH at 16 Mpc
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M87 Fringe Visibility Doeleman et al., Science (Express), Sept 25, 2012
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1924-292 uv Coverage of VLBI Experiment at 230 GHz, April 2009 Ru-Sen Lu et al., ApJ, 2012, in press
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Correlated Flux Density vs. uv Distance Correlated Flux Density vs. Time 1924-292 uv Plane Data
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1924-293 Phase Closure Data vs. Time
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230 GHz 43 GHz 5 GHz pc pc pc Images of 1924-292 Shen et al. 1997, 2002Ru-Sen Lu et al. 2012
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Summary 1.3mm VLBI confirms Rsch scale structure in M87 and Sgr A*. International collaboration forming strong EHT organization. Key technical advances under way and roadmap to full EHT by 2015 clear. Most effort low risk: greatest risk is funding. EHT is opening a new window on BH study. GLT is key new element to the EHT.
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