Searching for the Oldest Stars: Ancient Relics from the Early Universe, Anna Frebel, Princeton U. Press, 2015. $29.95 (302 pp.). ISBN 978-0-691-16506-6 Buy at Amazon
Metal-poor stars are a girl’s best friend! Who still needs diamonds?” Those final two sentences of Anna Frebel’s Searching for the Oldest Stars: Ancient Relics from the Early Universe express the author’s love of and passion for stellar archaeology, the quest to constrain the origin of elements through archaeological “digs” of the night sky. Throughout her book, Frebel conveys her enthusiasm in the way she interweaves a story of the cosmic origin of elements with a personal account of scientific discovery and methodology that gives readers a glimpse into the life and thrills of a modern-day astronomer.
All elements, except for hydrogen, helium, and lithium, have their origin in the interiors of stars: The iron in our blood, the calcium in our bones, and the carbon, nitrogen, and oxygen that make up the amino acids that are crucial for life itself—all were created in the interior furnaces of stars and then released by stellar explosions. As Carl Sagan put it in The Cosmic Connection: An Extraterrestrial Perspective (Doubleday, 1973), “We are made of star-stuff.” Although Frebel gives a detailed description of how various elements are synthesized in stellar interiors, she neglects to provide a physical description of primordial nucleosynthesis. It would have been fitting, in particular, to include an explanation of why elements heavier than lithium cannot have formed during the first three minutes after the Big Bang.
As one of the world’s leading researchers in the field of stellar archaeology, Frebel uses large telescopes to take spectra of stars and to search for the most metal-poor stars—that is, stars poorest in elements heavier than helium. Absorption lines in those spectra are the fingerprints that reveal the stars’ elemental makeup, and they take central stage in a captivating detective story of how the first stars formed only a few million years after the Big Bang.
Metal abundances in the universe build up over time, as more and more stars shed the elemental yields from which newer generations of stars form. As a consequence, metal-poor stars are also old. The astrophysicist’s hunt for the most metal-poor stars is thus much like the archaeologist’s hunt for the oldest forms of life. Frebel discovered several of “the most metal-poor stars known, some of which have metal abundances, relative to hydrogen, that are less than 1/250 000 of that in the Sun. Such stars are cosmic fossils that may well have been enriched by the ejecta of only a single supernova; thus they provide important insight regarding the elemental yields of the first population of exploding stars in the universe.
A unique aspect of Searching for the Oldest Stars is that each chapter is intended to stand alone, so the chapters need not be read in any particular order. Some chapters outline the detailed physical processes by which stars form and evolve. Others tell enthralling stories, such as the author’s account of the Australian bushfires that destroyed the Mount Stromlo Observatory in 2003 or her description of what it is like to spend weeks on end on a remote mountaintop observing the night skies. Readers of Physics Today should have no problem with the physical concepts that feature in the chapters describing the various nucleosynthetic burning stages in a star’s life or the neutron-capture processes that are responsible for the synthesis of elements heavier than iron. But readers less versed in basic physics and astronomy will find those chapters challenging and may find themselves flipping among chapters to weave a comprehensive picture.
Frebel’s delightful blend of science and personal stories has plenty to offer for readers ranging from nonscientists to professional astronomers. In addition, by highlighting the important role of women astronomers in the development of stellar spectroscopy, Frebel clearly strives to motivate and inspire future generations of female scientists. Laden with passion and excitement, Searching for the Oldest Stars accomplishes what it sets out to do—engage readers and provide insights into stellar archaeology and the motivations that propel scientists in their quest to answer fundamental questions.
Frank van den Bosch is an associate professor of astrophysics at Yale University in New Haven, Connecticut. Coauthor of the textbook Galaxy Formation and Evolution (Cambridge University Press, 2010), he studies galaxy formation, large-scale cosmic structure, and dark-matter halos.