Dr. Dustin Madison is a postdoctoral researcher in the Center for Gravitational Waves and Cosmology working with Professor Maura McLaughlin. In his newest publication in the journal Physical Review Letters, he discusses Gravitational Wave memory and how it still shapes the way we see space.
Bursts of gravitational waves are produced whenever extremely massive objects get flung about at relativistic speeds. These ripples in space slightly alter the observed distribution of objects in the sky. In their wake, bursts of gravitational waves leave behind a permanent residual distortion of space called "memory".
Gravitational wave memory can be likened to a change in the refractive index of space. With refraction in mind, the memory wavefront can be thought of as the interface between two regions of space with slightly different refractive indices and so light at the interface changes the angle of its travel.
(Refraction)
This paper describes how all the sources of light in the sky appear to be permanently jostled about by the memory of a gravitational wave event. So, when the billion-solar-mass black holes at the centers of two distant colliding galaxies came together and merged 100 million years ago, a loud burst with memory was generated and forever altered the apparent position of all the visible objects in the sky by a small amount.
Similarly, when the supernova that created the Crab Nebula exploded in the year 1054, a softer burst with memory was produced that again slightly warped the celestial sphere. In this way, every gravitational wave event that's ever occurred is encoded in the distribution of distant sources of light. This paper is a step towards understanding the encoded signature of these gravitational wave relics and determining whether it can ever be detected, potentially in the most ancient light in the Universe, the cosmic microwave background.
Journal link to article: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.125.041101