High-resolution Millimeter-VLBI Imaging of Sgr A*
  We present the highest resolution VLBI imaging observations of Sgr A* made at both 7 and 3.5 mm. These data reveal wavelength-dependent intrinsic sizes with an intrinsic emitting region at 3.5 mm of about 1 AU (at a distance of 8 kpc to the Galactic Center). When combined with the lower limit on the mass of Sgr A*, these size measurements provide strong evidence that Sgr A* is a super-massive black hole. We also detected a structural variation which results in an intrinsically symmetrical structure that increases in its intrinsic size by more than 25% at 7 mm. 
Zhi-Qiang Shen