Point a telescope at a quiet patch of the constellation Boötes and the usual cosmic web of galaxies, superclusters and dark matter filaments simply disappears. In its place sits the Boötes Void, nicknamed the Great Nothing: a roughly spherical supervoid about 700 million light years from Earth with a radius of about 62 megaparsecs, nearly 200 million light years across. A region that size should hold around 2,000 mature galaxies. Astronomers have found about 60.

This deep dive unpacks how Robert Kirshner and colleagues stumbled onto the void during a painstaking 1981 redshift survey, why proving an absence means mapping the bright shoreline of the Hercules superclusters rather than the dark interior, and how a void this large can exist within the Lambda CDM model at all. The answer is coalescence: several smaller voids whose shared walls we ...