Poisson-Arago spot for gravitational waves

Diffraction and interference represent characteristic behaviors of waves. We proposed a new diffraction effect of gravitational waves described by the exact diffraction solution of gravitational waves using the Heun function. We demonstrated that a bright spot, an effect analogous to the Poisson-Arago spot in optics, will appear when an ingoing (quasi-)plane gravitational waves is diffracted by a Schwarzschild black hole. For normal incidence (quasi)-plane waves with frequency 100 Hz (0.1 HZ) diffracted by the center black hole of the Milky Way, the time delay between the earth bathed in a bright spot and witness the minimum of the first dark stripe is 5.4 (5400) days. This new diffraction pattern could be detected by future ground-based and space-based gravitational wave detectors.