American Scientist

FIRST LIGHT: Switching on the Stars at the Dawn of Time (Revised and Updated Edition). Emma Chapman. Bloomsbury Sigma, 2025. $19.

“The universe began. Time started.” This description of what happened after the Big Bang serves as a focal point throughout Emma Chapman’s First Light: Switching on the Stars at the Dawn of Time. Most religions have a creation story, but by comparison, the Big Bang theory is a fairly new scientific idea, with evidence of leftover radiation from the Big Bang discovered only in the 1960s. Prior to this point, scientists thought that the universe had always existed, unchanged. But a beginning implies change. There was a first for everything—a first star, a first galaxy, a first black hole—and these firsts radically changed the universe. First Light takes us on a journey back to that very beginning, where the author considers what the first generation of stars looked like, and why researchers haven’t found evidence of their existence. As Chapman writes, “The first star is a species unto itself, a missing link that may now be extinct altogether.”

The book opens with a strong reminder of why missing evidence is a fundamental problem: Our current understanding of the early universe is not only incomplete, but we also don’t know what we don’t know. The author writes,

The absence of observations from the era of the first stars is alarming . . . In human terms, the missing cosmological data is equivalent to missing everything from the moment of conception to the first day of school. It may be a small fraction of time compared to the total lifetime, but when you consider how formative these early years are for humans, it is no wonder that astrophysicists quake at this much missing data . . . What incorrect conclusions are we coming to about the stars around us or how the universe is behaving now, because of this lack of data?

The entire narrative maintains this sense of wonder and humility. Chapman deftly illustrates many of the open questions in astronomy, such as: How big were the first stars? How did the first galaxies form? How did supermassive black holes form? What is dark matter? (Indeed, two of these questions drive my own research in galaxy evolution.) Chapman highlights the many difficulties of not being able to test a hypothesis in a lab, saying “The sheer scale of a modern-day astronomy experiment requires planning and dedication running back decades, and you can guarantee that as soon as a mission launches, groundwork will begin on the next experiment.” The universe is a strange place, and as Chapman points out, we astronomers don’t live long enough to see our questions answered.

To fully appreciate the questions in this book, the first chapters give the reader all of the fundamental astronomy they will need. Readers are introduced to the electromagnetic spectrum (light comes in many forms such as x-ray, microwave, and radio) and the principles of gravity governing the motion of celestial bodies. Most importantly for our field, readers learn that a galaxy’s “redshift” (how much its light has been stretched by the expansion of the universe), indicated by the variable z, correlates with where it sits in time. For example, my main body of research centers around galaxies and black holes when the universe was a mere 2 to 6 billion years old (or in astronomy lingo, at redshifts of z=1-3). You might think that this sounds like I’m looking far back in time, but the first stars and galaxies appeared when the universe was a mere 100 million years old, or likely even earlier. The truth is, we don’t know when the universe first lit up with stars, and the further back in time we look, the more we see.

The first stars were massive, lived short lives (well, millions of years), and exploded as violent supernovae. Astronomers have been searching for their remnants for decades—looking for fossil stars within the Milky Way and nearby dwarf galaxies, measuring the temperature of the gas in the early universe to look for heating through explosions, and through imaging unimaginably distant galaxies with the Hubble Space Telescope and the James Webb Space Telescope (JWST)—with no luck thus far. And this lack of evidence makes us wonder, is our technology simply not good enough? What experiment can we create that will finally see our Sun’s ancestors?

This point brings me to my main quibble with this book: It is outdated, even this “revised and updated” version, published five years after the original edition of 2020. JWST was designed to be a “first light” instrument (in other words, its aim was to find the very first galaxies and stars—later in its development process, the exoplanet science was attached, as exoplanets had only been discovered shortly before JWST was conceptualized), and as soon as it opened its shutters, our entire view of the early universe changed. Unfortunately, besides mentioning one high-redshift galaxy (z of 14, or when the universe was 300 million years old), the book leaves the most important part of the story out. This omission can be slightly forgiven as galaxy evolution is not Chapman’s main focus of study—but it is mine, and the oversights seem glaring. We have found several galaxies at even higher redshifts (17, 25, and possibly even 32!, when the universe was merely 90 million years young). This finding immediately presents a challenge to the repeated statement in this book that the first stars appeared when the universe was around 150 million years old. If the first galaxies are even older than that, there is something fundamentally missing from our understanding of how those first stars formed, and the book would have benefited from touching on this intriguing possibility.

What’s more interesting though, is that these galaxies seem to be more massive than should be possible. Something is wrong with our picture of galaxy formation, which this book presents as settled fact. Besides skipping over tantalizing JWST results, the book also contains a few factual inaccuracies, one of which I feel compelled to point out. Chapman claims that before the launch of JWST, the highest redshift galaxy found was a quasar (a galaxy actively forming a supermassive black hole, which can affect how star formation proceeds) at z=7.6 (the universe was 700 million years old), but this statement is not true. The record holder was a galaxy at redshift 11 (400 million years old). These ages matter, as they provide the conditions for how quickly the first stars formed, how many stars were formed, and how many generations of stars there had been. In simpler terms, Figure 1 in the book is wrong, and has been wrong for quite a while. Galaxies have been around for a very long time.

Given that caveat, the reader will still learn much valuable and interesting information about modern astronomical experiments, how stars form and die, and why the first stars are so hard to find. Chapman has an approachable and accessible writing style, often using analogies to illustrate difficult astronomical concepts. This book is aimed at nonastronomers, although even undergraduate majors would find it helpful, as it provides a very thorough overview of the field in an easier to digest format than a textbook.

I read this book over the course of three days, which is highly unusual for me. I’m often so exhausted by the end of the day that I read for 10 minutes before falling asleep, if at all. This book reinforces concepts throughout the text, making it accessible for someone with my reading style. Although each chapter introduces new concepts, it also builds upon previous chapters. Chapman provides brief summaries of previous concepts when they arise again, to refresh the reader’s memory and prevent them from having to search previous pages to figure out what is being discussed.

Overall, First Light presents an intriguing view of the early universe, weaving in historical discoveries and amusing personal anecdotes. The reader will leave with a newfound appreciation for the complexity of our universe and the challenges faced by modern astronomers, who themselves may never receive the answers they seek. As Chapman concludes,

Sometimes having a job that reminds you daily how insignificant you are can be . . . wearing. Largely, however, my connection with cosmology has been positive. . . . Somehow, [humans] have been able to stop fighting among themselves for long enough to plan for an experiment decades away. I feel as though I’ve been given tickets to the world’s greatest spectacle. That’s not depressing, that’s amazing.