Dinnertime for Sgr A The Black Hole in
Dinnertime for Sgr A* (The Black Hole in the Center of Our Galaxy) by James Moran Harvard-Smithsonian Center for Astrophysics University of Barcelona, October 5, 2012
Summary of Talk • The mass of the black hole in the Center of the Galaxy (Sgr A*) is about 4 x 106 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 M 87 and 1924 -293 have also been made at 1. 3 mm. (new) • Event Horizon Telescope (EHT) under development
Submillimeter Valley, Mauna Kea, HI
SMA in Intermediate Configuration About 0. 5 arcsec resolution at 1 mm
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 Rs) 1 mas / 0. 3 micro pc Marrone, Munoz, Zhao, Rao 3. Sgr. A* radio source 37 microarcseconds / 0. 01 microparsec Doeleman et al.
Nine Field Mosaic Image of Circumnuclear Disk in Galactic Center CN H 2 CO Si. O SMA Data Sergio Martin Ruiz 3 arcmin field 3 arcs resolution 1. 3 mm wavelength
Polarization Images at Various Wavelengths from the SMA 230 GHz 345 GHz 690 GHz
2005 SMA Measurements of Faraday Rotation in Sgr A* Important: SLOPE of polarization angle ~ constant in time at 230 GHz
Accretion Rate and Faraday Rotation c ( , t) = c 0(t) + 2 RM(t) RM = 8. 1 x 105� ne B× dl RM = – 5. 1 x 105 rad/m 2 Assumptions equipartition density power law inner radius cutoff of Faraday screen Accretion rate = 10– 9– 10– 7 MSun /yr
Polarization at Three Frequencies Simultaneously
Circular Polarization of Sgr A* Left handed CP at all frequencies measured!! (red) Stokes I (blue) Stokes V Fractional Circular Polarization vs. Frequency
Faraday Conversion in Sgr A* = 1 surface BH =1 =1 (diameter) GHz 230 22 1. 4 Rs 6 80 1600 mas 0. 06 0. 8 16 Faraday conversion phase shift = 109 L B 4 3 = /2 (optimum) B = magnetic field in Gauss L = length in pc = wavelength in m mode direction Range of = 1 surface between 1. 4 and 230 GHz: ~350 (based on R =1 ~ -1. 1) input signal mode direction in ultrarelativistic plasma
Some Scales in the Galactic Center
Simulation of the infrared observations of the stars orbiting the Galactic Center by the Genzel Group
What is the Central Mass Around Which These Stars Are Orbiting? T = 15. 2 years R = 0. 12 arcseconds = 17 light hours M = 4 million x the mass of the Sun Density > 1017 solar masses/pc 3
• Very faint source still detectible at most astronomical observing bands – SED measurements span 10 decades in frequency • LSgr. A* ~ 300 LSun ~ 10– 9 Eddington limit Submm Near IR Radio X-Ray Genzel et al. 2004 IR flare (Hornstein et al. 2007)
Black Hole “image” Dominated by GR The black hole “shadow” (Bardeen 1973; Falcke, Agol, Melia 2000; Johannsen and Psaltis 2010) Maximally spinning BH Free fall envelope Non-spinning BH Rotating accretion envelope Dshadow = 9/2 * Rsch Dshadow = sqrt(27) * Rsch Measuring the shadow gives Mass. (Johannsen, Psaltis et al. 2012)
Observations of Cygnus A with the Jodrell Bank Intensity Interferometer Square of visibility 125 MHz Jennison and Das Gupta 1952; see also Sullivan 20 0
Cygnus A with Cambridge 1 -mile Telescope at 1. 4 GHz 3 telescopes 20 arcsec resolution Ryle, Elsmore, and Neville, Nature, 205, 1259, 1965
Cygnus A with Cambridge 5 km Interferometer at 5 GHz 16 element E-W Array, 3 arcsec resolution Hargrave and Ryle, MNRAS, 166, 305, 1974
The Synchrotron Emission from Cygnus A Imaged with the VLA at 6 cm Wavelength
1. 3 mm Observations of Sgr A* 90 8 k m m k 0 3 40 m k 0 63 4 VLBI program led by a large consortium led by Shep Doeleman, MIT/Haystack
U-V Tracks
14 Rsch ( 0 as) Gaussian and Torus Fit to Visibility Data Gammie et al. Doeleman et al. 2008; Fish et al. 2011
Seeing Through the Scattering OBS deviates from scattering for cm INT SCAT for mm INT
Sgr A*’s View of the EHT GLT - Greenland IRAM LMT ALMA SPole
Progression to an Image GR Model 7 station 13 station Doeleman et al. , “The Event Horizon Telescope, ” Astro 2010: The Astronomy and Astrophysics Decadal Survey, Science White Papers, no. 68
Animation of Accretion Object Discovered by Genzel Group, 2012
M 87 at 5 GHz (insert) and 43 GHz Right ascension offset (mas) VLBA image at 43 GHz by Hada, et al. , Nature, 2011
VLBA Movie of M 87 at 43 GHz (7 mm) (Craig Walker et al. 2008) 6. 6 x 109 Solar Mass BH at 16 Mpc Beam: 0. 43 x 0. 21 mas 0. 2 mas = 0. 016 pc = 60 Rs 1 mas/yr = 0. 25 c
M 87 Fringe Visibility Doeleman et al. , Science (Express), Sept 25, 2012
1924 -292 uv Coverage of VLBI Experiment at 230 GHz, April 2009 Ru-Sen Lu et al. , Ap. J, 2012, in press
1924 -292 uv Plane Data Correlated Flux Density vs. uv Distance Correlated Flux Density vs. Time
1924 -293 Phase Closure Data vs. Time
Images of 1924 -292 5 GHz 0 pc Shen et al. 1997, 2002 43 GHz pc 230 GHz pc Ru-Sen Lu et al. 2012
Summary • 1. 3 mm VLBI confirms Rsch scale structure in M 87 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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