Early quasar illuminates a Universe without metals

The moments after the Big Bang left the Universe very hot and dense. In that violent environment, the first nuclei came to be: hydrogen, helium, and lithium…but nothing heavier. The elements more massive than helium (which astronomers perversely refer to as “metals”) were forged by stars and spread through the Universe as those stars died. That means if we look far enough back in time, we should be able to see the era of transition: when the first metals in the Universe came to be. A new observation of the environment surrounding a quasar shining a mere 772 million years after the Big Bang has revealed a metal-free cosmos.

Modern galaxies like the Milky Way contain populations of stars that we can divide based on their metal content. The Sun is a Population I star, with a relatively high metal abundance; older, Population II stars near the galactic center are metal-poor. However, the earliest, metal-free stars—known as Population III—are still hypothetical. According to widely accepted models, Population III stars were massive and therefore short-lived, going supernova and spreading the first metals into interstellar space.

When did these first stars form, and did they actually correspond to our models? These questions are still unanswered. The crucial period of time when the first stars must have formed is still marked by a paucity of data. [Read more…]

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