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American Association for the Advancement of Science

Stars may not be massive or metallic

Artistic view of gas around a forming galaxy in a large computer simulation. The pristine gas detected by astronomers could lie in one of the filamentary regions.
[Simulation by Ceverino, Dekel and Primack]

Before stars existed in space, the only elements present in the universe were hydrogen, helium and lithium. The birth of the first stars fundamentally transformed the early universe by emitting the first light and producing the first metals.

Astronomers are still trying to unlock some of the secrets of early star formation. Two new studies in the journal Science show that these early stars weren't as big or metallic as previously thought.

Here, Michele Fumagalli from the University of California, Santa Cruz and colleagues detected two stars without discernible metals, based on observations made with the Keck telescope in Hawaii.

Both stars were formed about two billion years after the Big Bang, a period that spawned plenty of stars and galaxies, most of which astronomers expect to have been enriched with metals.

However, the team's results imply that the transport of metals among stars and galaxies was not as efficient or widespread as previously thought. Previous studies have also suggested that the first stars were hundreds of times more massive than the Sun. Yet numerical simulations by Takashi Hosokawa and colleagues in a separate study reveal that early stars were probably much smaller.

Their calculations demonstrate the difficulty of growing the first stars to masses above a few tens of times that of the Sun. The results from both studies paint a slightly different picture of early star formation and suggest that stars still hold secrets worth exploring.