Missing Metals?

摘要

Before the first stars formed, the only elements present in the universe were hydrogen, helium, and lithium. All the other elements, which astronomers refer to as metals, were produced in stars. Fumagalli et al. (p. 1245, published online 10 November; see the Perspective by Kacprzak) report the detection of two gas clouds without discernible metals. These clouds date to about two billion years after the Big Bang, an epoch by which plenty of stars and galaxies had formed and thus by which most of the gas in the universe was expected to have been enriched with metals. Thus, the transport of metals from stars and galaxies to their surroundings was not as efficient or as homogeneous as previously assumed.