A rock-star astronomer searches for the oldest stars

Anna Frebel's research tells us much about the beginnings of the universe


Searching For The Oldest Stars by Anna Frebel.   No Credit.


Anna Frebel

A rock star among astronomers, Anna Frebel was the sort of kid boffin who could turn a not uncommon sense of wonder at the nature of things into a decidedly unordinary 55-page paper on “Analysis of colour-magnitude diagrams of selected star clusters from the viewpoint of stellar evolution.” That was when she was 17. The German-born Frebel, now 35 and an astrophysics prof at MIT, has become a leading figure in the hunt for metal-deficient stars. She’s actually discovered two of them, the blandly named HE 1327-2326, while still a doctoral student in 2005 and, just last year, the jewel in the hunters’ crown, the equally anodyne SM0313.

And what is so special about metal-poor stars, to the extent a self-described stellar archaeologist is fixated on them? The answer is in the title of Frebel’s book: they are very old indeed, and nothing else tells us as much about the beginnings of the universe. The Big Bang itself produced only hydrogen and helium (plus the merest trace of lithium) 13.8 billion years ago. The elements that make life possible, that make up us, in fact—including iron, oxygen and carbon—had to be created in stars. And that meant, Frebel points out, the existence of something unsuspected half a century ago: continuous stellar chemical evolution.

The first stars, massive beasts 100 times the size of the sun, were formed a few hundred million years after the Big Bang from the three original elements. Burning hot and fast, they had yet to synthesize much in the way of heavier elements before they soon went supernova and expelled those elements into the gas mix from which later stars were born. That first generation of stars is long gone, but second-gen examples like SM0313, probably 13 billion years old, are still around. By reading their spectrums, astronomers can recognize them.

One of the glories of astrophysics is the way it combines real-world uselessness with mind-blowing effects on human consciousness. Here, Searching For The Oldest Stars shines. Frebel deals with the evolution of scientific thinking on the nature of the universe, the formation of ideas on how to identify such stars, and the wearisome but hopeful search for individual examples, with real descriptive power. By the time she is excitedly noting how faint the calcium K line is in SM0313’s spectrum, and the adrenalin rush she felt when she couldn’t find iron lines at all, the reader is right there with her. But good popular exposition of specialized knowledge is not that rare—the core of Frebel’s book, and the source of its appeal, is the joy it conveys.

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