It carries the «imprint» of cold hydrogen gas that it passed through on its way here. (sciencedaily.com)
They routinely create hot plasma jets and gas bubbles that are thought to prevent the cooling of galaxies and regulate the formation of stars, which requires cold hydrogen gas as a building block. (ibtimes.com)
The astronomy team captured data from these two galaxies as they were during a period of cosmic history known as the Epoch of Reionization, when most of intergalactic space was suffused with an obscuring fog of cold hydrogen gas. (sciencedaily.com)