Approaching the event horizon: 1.3mmλ VLBI of SgrA*

Advances in VLBI instrumentation now allow wideband recording thatsignificantly increases the sensitivity of short wavelength VLBIobservations. Observations of the super-massive black hole candidate atthe center of the Milky Way, SgrA*, with short wavelength VLBI reducesthe scattering effects of the intervening interstellar medium, allowingobservations with angular resolution comparable to the apparent size ofthe event horizon of the putative black hole. Observations in April 2007at a wavelength of 1.3mm on a three station VLBI array have nowconfirmed structure in SgrA* on scales of just a few Schwarzschildradii. When modeled as a circular Gaussian, the fitted diameter of SgrA*is 37 μas (+16,-10; 3σ), which is smaller than the expectedapparent size of the event horizon of the Galactic Center black hole.These observations demonstrate that mm/sub-mm VLBI is poised to open anew window onto the study of black hole physics via high angularresolution observations of the Galactic Center.