Gravitational Wave Search through Electromagnetic Telescopes

We study the graviton-photon conversion in the magnetic fields of the Earth, the Milky Way, and intergalactic regions. Requiring that the photon flux converted from gravitons does not exceed the observed photon flux with telescopes, we derive upper limits on the stochastic gravitational waves in frequency ranges from 107-1035 Hz. Remarkably, the upper limits on h2 omega GW could be less than unity in the frequency range of 1018-1023 Hz in a specific case. The detection of gravitational waves using telescopes could open up a new avenue for high frequency gravitational wave observations.