A. Faisst

Deep inside a molecular cloud, where temperatures drop to 10–20 kelvin and gas densities reach a million particles per cubic centimeter, a frozen shadow prevails. There, far from starlight, water, carbon dioxide, and other molecules freeze onto dust grains.

A vast city lights new streetlamps every night. But then a hurricane sweeps in, rips all the fuel from the warehouses, and the lamps go out one by one. Something similar has been spotted by astronomers in a galaxy whose light has traveled 12.5 billion years to reach us.