The simultaneous spectrum of Sgr A* from 20cm to 1mm and the nature of   the mm-excess
  We report results from a multiwavelength campaign to measure the simultaneous spectrum of the super-massive black hole candidate Sgr A* in the Galactic Center from cm to mm-wavelengths using the VLA, BIMA, the Nobeyama 45m, and the IRAM 30m telescopes. The observations confirm that the previously detected mm-excess is an intrinsic feature of the spectrum of Sgr A*. The excess can be interpreted as due to the presence of an ultra-compact component of relativistic plasma with a size of a few Schwarzschild radii near the black hole. If so, Sgr A* might offer the unique possibility to image the putative black hole against the background of this component with future mm-VLBI experiments. 
Heino Falcke (U. Maryland/MPIfR Bonn), W.M. Goss (NRAO), Hiroshi   Matsuo (Nobeyama), Peter Teuben (Univ. Maryland), Jun-Hui...