The High-Energy Activity of the Supermassive Black Hole at the Galactic Center

Andrea Goldwurm

For more than three decades astrophysicists have searched for the
high-energy signature of Sgr A*, the radio source that is now
compellingly associated to the supermassive black hole at the center
of our galaxy.  This quest has finally led to the discovery of X-ray
flares from this source, that, inspite of involving a very low power
compared to the potential of the object, do allow us to explore the
processes occuring at few tens of gravitational radii from the black
hole horizon.  I will review the milestones of this long search and
the most recent results obtained in this field, in the more general
context of the high-energy activity of the galactic center region. I
will also show how recent measurements in X-rays and gamma-rays of the
molecular clouds of the region demonstrate that Sgr A* was much more
luminous in the recent past, making the galactic supermassive black
hole more similar, than appear from its present activity, to
low-luminosity active galactic nuclei.