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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

An Event Horizon vs a Surface

Radiative Efficiency of accreting gas

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


(~700 times more massive than SgrA*)

(~2000 times farther than SgrA*)


(Broderick & Loeb 2008)

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

Walker 2008

1 3 mm images
1.3 mm Images




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


Anisotropic emission of gravitational waves  momentum recoil

galaxies as bubble chambers for bhs ejected by gravitational wave recoil
Galaxies as “Bubble Chambers”for 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

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

  • 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