A stone falls into a pond — ripples spread across the water. If the stone doesn't fall but whizzes over the surface at tremendous speed, a straight wave runs along the water. When it hits a floating log, ripples spread out from the point of impact. That's roughly how gravity works in the new study.
The study examines a pair: an ultra-fast particle (like that stone) and a heavy stationary body (the log). The fast particle creates a planar gravitational wave around itself — a ripple in the fabric of space. When this ripple reaches the massive body, it perturbs its field, and a secondary spherical wave arises, spreading in all directions. The authors have for the first time computed its strength and shape analytically, that is, they obtained exact equations rather than just numerical estimates.
Such a scenario is not just a mathematical exercise. In space, particles with enormous energy do fly past stars and black holes. The spherical wave born in this process may carry information about how gravity works in strong fields, and someday sensitive detectors might register it.
Gravitational waves are so weak that even from a collision of black holes, they stretch a kilometer-sized detector by a thousandth of the size of a proton.
In Carl Sagan's novel "Contact," aliens use gravitational waves to transmit messages across the galaxy.