A Forty Year Journey
  I try to describe the stepwise progress in proving that massive black holes
do exist in the Universe. As compared to forty years ago, measurements have
pushed the 'size' of the 4 million solar mass concentration in the Galactic
Center downward by almost 10^6, and its density up by 10^18. Looking ahead
toward the future, the question is probably no longer whether SgrA* must be a
MBH, but rather whether GR is correct on the scales of the event horizon,
whether space-time is described by the Kerr metric and whether the 'no hair
theorem' holds. Further improvements of the VLT interferometer GRAVITY (to
GRAVITY+) and the next generation 25-40m telescopes (the ESO-ELT, the TMT and
the GMT) promise further progress. A test of the no hair theorem in the
Galactic Center might come from combining the stellar dynamics with EHT
measurements of the photon ring of SgrA*.
