Ice in a million-degree Fermi bubble reveals the Milky Way’s recent eruption

Astronomers using the Green Bank Telescope spotted surprisingly cold, dense hydrogen clouds embedded inside the Milky Way’s vast, super-hot Fermi bubbles—structures thought to be created by a recent, violent outburst from the galaxy’s core. Because such chilled gas should evaporate quickly in million-degree surroundings, its survival hints that the bubbles are only about a million years old. Ultraviolet data from Hubble backs the discovery, and the clouds’ million-mph speeds reinforce the bubbles’ youth. The find forces scientists to rethink how energy and matter flow through galaxies.