  If the dark halo of our galaxy is made of compact objects as massive as M =
10^6 solar masses, their detection by means of ordinary microlensing searches
would take a very long time as the characteristic time scale of such a lensing
event, t_0, is approximately 200 years. Fortunately, the very high
magnification events of the numerous faint stars, which are normally well below
the detection threshold, have short duration peaks with a characteristic time
scale of only t_0 / A_{max}, where A_{max} >> 1 is the peak magnification
factor. The two almost equally bright images are separated by approximately 2''
(M/10^6 solar masses )^{1/2}, and they rotate very rapidly around the lens with
the relative proper motion enhanced by a factor 2 A_{max}. The same events will
offer an opportunity to study spectroscopically stars which are normally far
too faint to be reached.
