Gravitational glint: Detectable gravitational wave tails from stars and compact objects

TL;DR

This paper predicts that gravitational waves scatter off compact objects creating detectable delayed echoes, called 'gravitational glint', which can be used to map the universe and study object interiors.

Contribution

It introduces the concept of gravitational glint as a detectable effect of gravitational wave tails caused by scattering off compact objects.

Findings

Gravitational waves are scattered by stars, white dwarfs, neutron stars, and dark matter candidates.

The scattered signals, 'glints', are potentially detectable as delayed echoes.

This phenomenon enables new methods for mapping the universe and probing object interiors.

Abstract

Observations of a merging neutron star binary in both gravitational waves, by the Laser Interferometer Gravitational-wave Observatory (LIGO), and across the spectrum of electromagnetic radiation, by myriad telescopes, have been used to show that gravitational waves travel in vacuum at a speed that is indistinguishable from that of light to within one part in a quadrillion. However, it has long been expected mathematically that, when electromagnetic or gravitational waves travel through vacuum in a curved spacetime, the waves develop "tails" that travel more slowly. The associated signal has been thought to be undetectably weak. Here we demonstrate that gravitational waves are efficiently scattered by the curvature sourced by ordinary compact objects -- stars, white dwarfs, neutron stars, and planets -- and certain candidates for dark matter, populating the interior of the null cone. The resulting "gravitational glint" should imminently be detectable, and be recognizable (for all but planets) as briefly delayed echoes of the primary signal emanating from extremely near the direction of the primary source. This opens the prospect for using GRAvitational Detection And Ranging (GRADAR) to map the Universe and conduct a comprehensive census of massive compact objects, and ultimately to explore their interiors.