  The detection of fast variations of the TeV (10^12 eV) gamma-ray flux, on
time-scales of days, from the nearby radio galaxy M 87 is reported. These
variations are ~10 times faster than that observed in any other waveband and
imply a very compact emission region with a dimension similar to the
Schwarzschild radius of the central black hole. We thus can exclude several
other sites and processes of the gamma-ray production. The observations confirm
that TeV gamma-rays are emitted by extragalactic sources other than blazars,
where jets are not relativistically beamed towards the observer.
