Galaxies Are Wrapped in a Hidden Sea of Hot Gas Far Bigger Than Their Stars
A galaxy in a photograph looks like a cluster of stars, but the real thing extends far beyond that: a diffuse cloud of gas, wider than the visible galaxy, that supplies the raw material for future stars. NASA's small satellite ASPERA is designed to catch this invisible gas in ultraviolet light, and SORABUMI explains how galaxies grow by inhaling and exhaling it.