Joint Astrophysics Colloquium

Observing an Event Horizon: Submm-VLBI of SgrA*

Shepard Doeleman

MIT Haystack Observatory

There is now very strong evidence that SgrA*, the compact source of radio, IR, and x-ray emission at the Galactic Center, marks the position of a 4 million solar mass black hole. Only 8 kilo-parsecs away, Very Long Baseline Interferometry (VLBI) has the potential to model, and eventually image, emission on scales of a few Schwarzschild radii, at the innermost accretion region of this black hole. This requires pushing the VLBI technique to short wavelengths where scattering by the ionized ISM is reduced and the intrinsic structure of SgrA* can be observed.

VLBI observations in April 2007 at a wavelength of 1.3mm have now confirmed structure in SgrA* on scales of just a few Schwarzschild radii. More sensitive observations, using additional VLBI stations, are planned over the next few years, and will be sensitive to time variable structures predicted by models of flaring activity in SgrA*. I will describe the instrumentation efforts that enable these observations, and discuss what current and future VLBI observations of SgrA* tell us about this closest super-massive black hole.