Some astrophysical consequences due to the existence of magnetic monopoles

This paper reviews the theory of the magnetic monopole as an astrophysical object. In particular we construct a model by which we are able to calculate the mass of the monopole by the unique assumption that the source of energy of quasars is due to monopole-antimonopole annihilation, without referring to particular GUTs. It results that the mass of the monopole must be 1016 GeV, i.e., the monopole predicted by the Georgi-Glashow model.