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 rF ∝ √1 AU/f and the solar radius r ⊙. This solar diffraction is potentially detectable through its frequency-dependent amplification of the wave. The detection rate with Einstein Telescope is estimated to be ∼ 1/1000 per year, with the optical depth ∝ (solar angular area on the sky)/4π. High-frequency regimes of merger and ringdown phases are found to be crucial. In addition to the discovery, we advocate that solar diffraction allows probing the inner solar density profile, as rF sweeps a range of solar radius during the chirping. These physics are captured by a formalism in terms of convergence and shear, which allows much easier estimation and more intuitive understanding. Solar diffraction can be a new opportunity with ongoing and future LIGO-band missions.