Every year, hundreds of thousands of pairs of black holes merge in a cosmic dance that emits gravitational waves in every direction. Since 2015, the large ground-based LIGO, Virgo and KAGRA interferometers have made it possible to detect these signals, although only about a hundred such events, an infinitesimal fraction of the total, have been observed. Most of the waves remain 'indistinguishable', superimposed and added together, creating a flat, diffuse background signal that scientists call the 'stochastic gravitational wave background' (SGWB). New SISSA research, published in The Astrophysical Journal, proposes using a constellation of three or four space interferometers to map the flat and almost perfectly homogeneous background in a search for ripples. These small fluctuations, known to scientists as anisotropies, hold the information needed to understand the distribution of gravitational wave sources on the largest cosmological scale.
Image: Simon Barke (University of Florida)