The radiative decay of sterile neutrinos with typical masses of 10 keV
is investigated in the presence of a strong magnetic field and degenerate
electron plasma. The modification of the photon dispersion relation by
the active external medium is taken into account. The limiting cases
of relativistic and non-relativistic plasma are analyzed. The decay rate
in a strongly magnetized plasma as a function of the plasma electron number
density is compared with the unmagnetized case. It Was found that the strong
magnetic field suppresses the catalyzing influence of the electron plasma
on the decay rate.