J. Xavier Prochaska

The night of March 4, 2024. The MeerKAT radio telescope in South Africa catches a millisecond pulse: a fast radio burst coming from a depth of 17.4 gigaparsecs. This is light that traveled 10.5 billion years to reach Earth.

The night sky looks smooth, but it's actually clumpy — vast communities of galaxies that bend light from distant objects like lenses. When a short, powerful radio burst goes off somewhere in the universe, its path to an Earth telescope can pass near such a clump.

Around every galaxy lies an invisible corona of cold gas. It extends far beyond the stellar disk and serves both as a fuel depot for new stars and as a graveyard for ejected material.