Gravitational wave memory: Further examples

Ehlers and Kundt [J. Ehlers and W. Kundt, Exact solutions of the gravitational field equations, in Gravitation: An Introduction to Current Research, ed. L. Witten (Wiley, New York, 1962)] argued in favor of the velocity effect: particles initially at rest hit by a burst of gravitational waves should fly apart with constant velocity after the wave has passed. Zel'dovich and Polnarev [Y. B. Zel'dovich and A. G. Polnarev, Radiation of gravitational waves by a cluster of superdense stars, Astron. Zh. 51 (1974) 30, [Sov. Astron. 18 (1974) 17]] suggested instead that waves generated by flyby would merely displace the particles, as illustrated here by further examples.