The Jet in the Galactic Center: An Ideal Laboratory for
  Magnetohydrodynamics and General Relativity
  In this paper we review and discuss some of the intriguing properties of the
Galactic Center supermassive black hole candidate Sgr A*. Of all possible black
hole sources, the event horizon of Sgr A*, subtends the largest angular scale
on the sky. It is therefore a prime candidate to study and image plasma
processes in strong gravity and it even allows imaging of the shadow cast by
the event horizon. Recent mm-wave VLBI and radio timing observations as well as
numerical GRMHD simulations now have provided several breakthroughs that put
Sgr A* back into the focus. Firstly, VLBI observations have now measured the
intrinsic size of Sgr A* at multiple frequencies, where the highest frequency
measurements have approached the scale of the black hole shadow. Moreover,
measurements of the radio variability show a clear time lag between 22 GHz and
43 GHz. The combination of size and timing measurements, allows one to actually
measure the flow speed and direction of magnetized plasma at some tens of
Schwarzschild radii. This data strongly support a moderately relativistic
outflow, consistent with an accelerating jet model. This is compared to recent
GRMHD simulation that show the presence of a moderately relativistic outflow
coupled to an accretion flow Sgr A*. Further VLBI and timing observations
coupled to simulations have the potential to map out the velocity profile from
5-40 Schwarzschild radii and to provide a first glimpse at the appearance of a
jet-disk system near the event horizon. Future submm-VLBI experiments would
even be able to directly image those processes in strong gravity and directly
confirm the presence of an event horizon.
