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)

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 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 (new) VLBI observations of M87 and 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 R s ) 1 mas / 0.3 micro pc Marrone, Munoz, Zhao, Rao 3. SgrA* radio source 37 microarcseconds / 0.01 microparsec Doeleman et al.

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

230 GHz345 GHz 690 GHz Polarization Images at Various Wavelengths from the SMA

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 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  

Polarization at Three Frequencies Simultaneously

Circular Polarization of Sgr A* (red) Stokes I (blue) Stokes V Fractional Circular Polarization vs. Frequency Left handed CP at all frequencies measured!!

Faraday Conversion in Sgr A* GHz   =1 R s   =1 (diameter) mas 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

Some Scales in the Galactic Center

Simulation of the infrared observations of the stars orbiting the Galactic Center by the Genzel Group

T = 15.2 years R = 0.12 arcseconds = 17 light hours M = 4 million x the mass of the Sun Density > solar masses/pc 3 What is the Central Mass Around Which These Stars Are Orbiting?

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 X-Ray Radio Submm Near IR 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) 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

Observations of Cygnus A with the Jodrell Bank Intensity Interferometer Square of visibility 125 MHz Jennison and Das Gupta 1952; see also Sullivan 

Cygnus A with Cambridge 1-mile Telescope at 1.4 GHz Ryle, Elsmore, and Neville, Nature, 205, 1259, telescopes 20 arcsec resolution

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

The Synchrotron Emission from Cygnus A Imaged with the VLA at 6 cm Wavelength

1.3 mm Observations of Sgr A* 4630km VLBI program led by a large consortium led by Shep Doeleman, MIT/Haystack 4030km 908km

U-V Tracks

Gaussian and Torus Fit to Visibility Data Gammie et al. 14 Rsch (  as)  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   IRAM SPole GLT - Greenland

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

Animation of Accretion Object Discovered by Genzel Group, 2012

 at 5 GHz (insert) and 43 GHz Right ascension offset (mas) VLBA image at 43 GHz by Hada, et al., Nature, 2011

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

M87 Fringe Visibility Doeleman et al., Science (Express), Sept 25, 2012

uv Coverage of VLBI Experiment at 230 GHz, April 2009 Ru-Sen Lu et al., ApJ, 2012, in press

Correlated Flux Density vs. uv Distance Correlated Flux Density vs. Time uv Plane Data

Phase Closure Data vs. Time

230 GHz 43 GHz 5 GHz  pc  pc  pc Images of Shen et al. 1997, 2002Ru-Sen Lu et al. 2012

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.