Astronomical observations at the x-ray, optical, and radio frequencies are used to show that the lifetime of neutrinos for radiative decay divided by the rest mass, $\frac{{\tau }_0}{m_{\nu }}$, exceeds ${10}^{17}$ sec/eV. If one makes the further assumption that $m_{\nu }>{10}^{-3\mathrm{}}$ eV, then ${\tau }_0>~{10}^{19}$ sec. If there are other competing decays of neutrinos, it is then shown that $\frac{{\Gamma }_{{\nu }_e}({\nu }_e\to x+\gamma )}{{\Gamma }_{{\nu }_e}\left(\mathrm{total}\right)}<~{10}^{-15\mathrm{}}$ and $\frac{{\Gamma }_{{\nu }_{\mu }}({\nu }_{\mu }\to x+\gamma )}{{\Gamma }_{{\nu }_{\mu }}\left(\mathrm{total}\right)}<~3\times {10}^{-6\mathrm{}}$.

• Received 13 April 1977

DOI:https://doi.org/10.1103/PhysRevLett.39.784