May 4, 2000 CfA Colloquium

Title: The First Accelerations Measurements of Stars Around Agr A*: Pinpointing and Characterizing the Galaxy's Central Massive Black Hole

Speaker: Andrea Ghez

Abstract: Four years ago, we initiated a proper motion study of the Galaxy's central stellar cluster using diffraction-limited K[2.2 micron]-band images obtained with the W.M. Keck I 10-m telscope. With relative positional accuracies of 2 milliarcsec, we have been able to measure stars moving with velocities up to 1400 km/s and, for the first time ever, accelerations of 3 mas/yr^2 (0.4 cm/s^2) at projected distances from the apparent radio counterpart of the black hole, Sgr A*, down to 0.004 pc (0.1 arcsec). These measurements have not only provided us with direct dynamical evidence for a 2.6 x 10^6 Mo central black hole, but have also permitted us to begin to constrain the orbits of these stars, which all appear to be bound to the central mass.

Reference for students: Ghez et al. 1998, ApJ, 509, 678
Lunch on Thursday 5/4 at 1:00 pm in Phillips.