  Gamma Ray Bursts (GRBs) are the most explosive events after the big bang:
their energy output corresponds to a sizeable fraction of a solar mass entirely
converted into energy in a few seconds. Although many questions about their
progenitors remain to be answered, it is likely that they are generated by a
newly formed and fast spinning black hole. The colossal power characterizing
GRBs is carried by a surprisingly small amount of matter, which is accelerated
to speeds differing from c by one part in ten thousands. GRBs are then the most
(special and general) relativistic objects we know of. Since GRBs are the
brightest sources at high redshift, albeit for a limited amount of time, they
are also the best torchlights we have to shine the far universe.
