Solar Diffraction of LIGO-Band Gravitational Waves

Abstract

We show that chirping gravitational waves in the LIGO frequency band $f=1 - 5000$ Hz can be gravitationally diffracted by the Sun, due to the coincidence of its Fresnel length $r_F \propto \sqrt{1\, {\rm AU}/f}$ and the solar radius $r_\odot$. This solar diffraction is detectable through its frequency-dependent amplification of the wave, albeit with low event rates. We also advocate that solar diffraction allows probing the inner solar profile with the chirping evolution of frequencies. Along the course, we develop diffractive lensing in terms of simple convergence and shear of a lens and emphasize the relevance of high-frequency regimes including merger and ringdown phases for detection. This work not only presents an interesting opportunity with ongoing and future LIGO-band missions but also develops the diffractive lensing of long-wavelength waves in the universe. A similar phenomenon can also help discover non-relativistic wave dark matter, as studied in a sequel.