  Motivated by the stringent flux limits for UHE neutrinos coming from gamma
ray burst or active galactic nuclei, we explore the possibility that the active
neutrinos generated in such astrophysical objects could oscillate to sterile
right handed states due to a neutrino magnetic moment mu_nu. We find that a
value as small as mu_nu ~1E-15 mu_B could produce such a transition thanks to
the intense magnetic fields that are expected in these objects.
