  Black holes are the densest form of energy, and in the presence of compact
dimensions black objects may take one of several forms including the black-hole
and the black-string, the simplest relevant background being R^{3+1} * S^1.
Recent understanding of the first order nature of the transition indicate a
powerful ``hysteresis'' curve, where black objects may undergo fusion or
fission during a tachyonic decay with Planck power and duration of the order of
the size of the compact dimension L. Such explosions which scale with L could
be test signatures for large extra dimensions in either astronomical
observations or accelerators.
