  The gravitational collapse of a non-rotating, black-hole-forming massive star
is studied by neutrino-radiation-hydrodynamical simulations for two different
sets of realistic equation of state of dense matter. We show that the event
will produce as many neutrinos as the ordinary supernova, but with distinctive
characteristics in luminosities and spectra that will be an unmistakable
indication of black hole formation. More importantly, the neutrino signals are
quite sensitive to the difference of equation of state and can be used as a
useful probe into the properties of dense matter. The event will be unique in
that they will be shining only by neutrinos (and, possibly, gravitational
waves) but not by photons, and hence they should be an important target of
neutrino astronomy.
