Cosmic global strings dissipate their energy into Nambu-Goldstone bosons with a $\frac{1}{k}$ energy spectrum. These Nambu-Goldstone bosons can convert to photons in the magnetic fields of various astrophysical objects, in particular galactic halos, clusters of galaxies, and extended radio sources. Evidence that this does in fact occur is found in cosmic-ray and radio-astronomy data.

• Received 18 April 1988

DOI:https://doi.org/10.1103/PhysRevLett.61.783