FIRST LIGHT

An update on the early years of the cosmos.

In her first nonfiction book, Chapman reviews the history, including new discoveries which have overturned accepted theories on the evolution of the universe, but she reserves most of her excitement for the “dark ages”—from 380,000 to roughly 1 billion years after the Big Bang. The early universe was a superheated soup of subatomic particles and energy. After nearly 400,000 years, the temperature had dropped enough to allow electrically neutral atoms to form and photons to travel freely. There was light and gas but nothing else. As it expanded and cooled, its matter—almost all hydrogen and helium—drifted about. Eventually, some clouds drifted together, and gravity began to pull. The clouds shrank and grew hotter, and a collapsing cloud grew so hot—millions of degrees—that its hydrogen became helium in a process known as fusion, which produces titanic amounts of energy. These were the first stars, born perhaps 180 million years after the Big Bang. Mostly brighter, hotter, bigger, and shorter-lived than today’s, they ended their lives and blew up, which produced “metals” (in astrophysics, elements other than hydrogen and helium) and scattered them, a process that formed other stars and eventually planets and humans. Do any primordial, metal-free stars still exist? The big ones are long gone, but small, sunlike stars have extremely long lifetimes. Evidence for their existence is turning up in obscure regions, such as dwarf galaxies and the outskirts of the Milky Way. Detecting them requires massive observatories, high-tech spectrographs, and the soon-to-be-launched $10 billion James Webb space telescope. Clearly fascinated by her subject, Chapman works diligently to describe the early universe, gradually introducing information about the life cycles of stars and techniques astrophysicists use to search for them. Her careful step-by-step explanations delve far deeper than a NOVA documentary, so readers must pay attention, but most will find it worth the effort.

Good astrophysics for committed readers.