The Archaeology of the Stars

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Four years ago, Anna Frebel, a young astronomer at the Massachusetts Institute of Technology, found an ancient star in a neighboring galaxy whose chemical composition proved nearly identical to some unusual stars on the outskirts of our own galaxy, which are older than the Milky Way itself.

It was a striking discovery, suggesting that the relatively young Milky Way is growing by conquest — “cannibalizing” nearby older dwarf galaxies. And it underscored the importance of a new way of learning how the universe evolved from the Big Bang to the modern cosmos.

Traditionally, astronomers study the early universe by looking back in time — peering deeper and deeper into space for vestiges of light from billions of years ago. But in the last decade, Dr. Frebel and others have used powerful telescopes and high-resolution spectroscopes to study the chemical composition of very old stars closer to home, in the Milky Way’s halo, producing a wealth of information about the creation of elements and the formation of the first stars and galaxies.

These astronomers are like Egyptologists combing the desert for relics of bygone civilizations, and call themselves stellar archaeologists. Their work relies on the fact that the rare, primordial stars they are looking for have very few atoms heavier than hydrogen and helium, the gases from which they came together. By contrast, our sun and other relatively young stars are rich in other elements, which astronomers collectively refer to as metals.

Written By: Curtis Brainard
continue to source article at nytimes.com

1 COMMENT

  1. @OP link – It was a striking discovery, suggesting that the relatively young Milky Way is growing by conquest — “cannibalizing” nearby older dwarf galaxies. And it underscored the importance of a new way of learning how the universe evolved from the Big Bang to the modern cosmos.

    I’m not sure this is a particularly new discovery. Small satellite galaxies merging into ours has been known for some time.

    Their work relies on the fact that the rare, primordial stars they are looking for have very few atoms heavier than hydrogen and helium, the gases from which they came together. By contrast, our sun and other relatively young stars are rich in other elements, which astronomers collectively refer to as metals.

    During various burning stages of those first stars’ evolution, before and after they exploded, their intense heat fused the hydrogen and helium atoms into heavier elements — the first metals — which in turn enabled the formation of long-lived, low-mass stars.

    ..and also allowed the formation of rocky planets.

    It should be made clear that the astronomical use of the term “metals” refers to all elements heavier than hydrogen and helium – not just the elements known as “metals” in chemistry.

    In astronomy and physical cosmology, the metallicity (also designated Z[1]) of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium. Because stars, which comprise most of the visible matter in the universe, are composed mostly of hydrogen and helium, astronomers use for convenience the blanket term “metal” to describe all other elements collectively.[2] Thus, a nebula rich in carbon, nitrogen, oxygen, and neon would be “metal-rich” in astrophysical terms even though those elements are non-metals in chemistry.

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