  We revisit the constraints implied by SN 1987 A observations on the decay
rate of a multi-MeV $\nu_\tau$ decaying into the visible channel $\nu_\tau
\rightarrow e^+ e^- \nu_e$, if its lifetime is more than 10 {\it sec.}. We
discuss its implication for the minimal left-right symmetric model with see-saw
mechanism for neutrino masses. We also speculate on the possible formation of a
``giant Capacitor" in intergalactic space due to the decay of "neutronization"
$\nu_\tau$'s and spin allignment possibility in the supernova.
