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Case Western Reserve University May 19, 2009. Imaging Black Holes. Testing theory of gas accretion: disks, jets Testing General Relativity: strong field gravity. Avi Loeb Institute for Theory & Computation Harvard University.

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Imaging Black Holes

  • Testing theory of gas accretion:disks, jets

  • Testing General Relativity:strong field gravity

Avi Loeb

Institute for Theory & Computation

Harvard University

The black hole in the galactic center sgra vlt with adaptive optics
The Black Hole in the Galactic Center: SgrA* VLT with Adaptive Optics

  • “3-color”: 1.5 - 3 um

  • 8.2 m VLT telescope

  • CONICA (IR camera)

  • NAOS (adaptive optics)

  • 60 mas resolution

S stars orbits around sgra
S-Stars Orbits Around SgrA*

(BH at rest in GC)

Ghez et al. 2008; Genzel et al. 2008

Can you hear me now
Can you hear me now?

10 million km

No, but no worries - you will be able to hear us for ~10 minutes until you reach the singularity…

Is general relativity a valid description of strong gravity?

*Infrared variability of flux (Genzel et al.) and polarization (Eckart et al.) of SgrA*: hot spots.

*Innermost Stable Circular Orbit: radius of 30 (10) micro-arcsecond and orbital time of 30 (8) minutes for a non-rotating (maximally-rotating) black hole at the Galactic center

*A hot spot would result in infrared centroid motion (GRAVITY-VLT) and could be imaged by a Very Large Baseline Array of (existing) sub-millimeter observatories. Targets:SgrA* and M87

Broderick & Loeb 2005

Three fortunate coincidences
Three Fortunate Coincidences

  • The accretion flow of SgrA* becomes transparent to synchrotron self-absorption at wavelengths shorter than 1 millimeter

  • Interstellar scattering ceases to blur the image of SgrA* on horizon scales at wavelengths shorter than 1 millimeter

  • The horizon scale of SgrA* and M87 (tens of micro-arcseconds) can be resolved by a Very Large Baseline Array across the Earth at wavelengths shorter than 1 millimeter


230 GHz

with interstellar scattering

345 GHz

with interstellar scattering

Different orbital phases of the hot spot 

Preliminary data
Preliminary Data

  • Doeleman et al.(2008)detected SgrA* on 3.5 Giga-lambda baseline (JCMT/SMTO) at 230 GHz (1.3mm), confirming structure on <40 micro-arcseconds(scattering scale ~25x13).

  • Reid et al. (2008) used VLBA to limit the variability in the centroid position of Sgr A* relative to a background quasar at 43GHz (7mm) to <100 +/-50 micro-arcsec for time scales between 50 and 200 minutes

1 3mm vlbi doeleman et al 2008 aro smt arizona carma california jcmt hawaii
1.3mm VLBI (Doeleman et al. 2008) wavelengthsARO/SMT (Arizona); CARMA(California); JCMT (Hawaii)

An Event Horizon vs a Surface wavelengths

Radiative Efficiency of accreting gas

Broderick, Loeb, & Narayan 2009 (arXiv:0903.1105)

M87 wavelengths

(~700 times more massive than SgrA*)

(~2000 times farther than SgrA*)

(Broderick & Loeb 2008) wavelengths

44GHz, (7 mm) VLBA Junor, Biretta, & Livio (1999)

Walker 2008

1 3 mm images
1.3 mm Images wavelengths




0 87 mm images
0.87 mm Images wavelengths




The forthcoming collision between the milky way and andromeda
The Forthcoming Collision Between the Milky-Way and Andromeda

  • The merger product is the only cosmological object that will be observable to future astronomers in 100 billion years

  • Collision will occur during the lifetime of the sun

  • The night sky will change

  • Simulated with an N-body/hydrodynamic code (Cox & Loeb 2007)

  • The only paper of mine that has a chance of being cited in five billion years…

X ray image of a binary black hole system in ngc 6240
X-ray Image of a binary black hole system in NGC 6240 Galaxies



Komossa et al. 2002

0402 379 rodriguez et al 2006 9
0402+379 (Rodriguez et al. 2006-9) Galaxies

  • Projected separation: 7.3 pc,

  • Estimated total mass:

VLBI at 1.35 GHz

Viscous dissipation of gravitational waves in a thin accretion disk
Viscous Dissipation of Gravitational Waves in a Thin Accretion Disk

 Equal heating per log radius

Kocsis & Loeb, Arxiv:0803.0003 (2008)

Gravitational wave recoil1
Gravitational Wave Recoil Accretion Disk


Anisotropic emission of gravitational waves  momentum recoil

 t Accretion Diskest particles with remain bound

Galaxies as bubble chambers for bhs ejected by gravitational wave recoil
Galaxies as “Bubble Chambers” Accretion Diskfor BHs ejected by gravitational wave recoil

Bonning, Shields & Salviander 2007

Schnittman & Buonanno 2007

Quasar Velocity Offset

<4% with kicks >500 km/s

<0.35% with >1000 km/s

Ionization trail

Loeb, PRL, 2007; astro-ph/0703722

Effect of recoil on bh growth and feedback
Effect of Recoil on BH Growth and Feedback Accretion Disk

440 km/s

740 km/s

Only a 10% increase in BH mass

Blecha & Loeb arXiv:0805.1420

Star clusters around recoiled black holes in the milky way halo
Star Clusters Around Recoiled Black Holes in the Milky Way Halo

escape(dwarf) <<kick ~hundreds of km/s <<escape(MW)

O’Leary & Loeb,arXiv:0809.4262

Highlights Halo

  • Direct imaging of the nearest supermassive black holes (SgrA*, M87) might become feasible within the next few years

  • GW-recoiled black holes have observable signatures: offset quasars, floating star clusters in the Milky-Way, electromagnetic counterparts to LISA sources