Following the first stars – Physics World

Physics
Taken from the December 2020 issue of Physics World. Members of the Institute of Physics can enjoy the full issue via the Physics World app.

Metaphorical Christmas Emma Chapman’s new book uses familiar elements of the holiday season to help explain the earliest stars. (Courtesy: iStock/da-kuk)

With Christmas looming just around the corner, it will soon be time for one of my favourite festive traditions: considering the physics of Santa Claus. Not a year seems to go by without some enchanting new theory on how Saint Nick manages to pull a fast one on the laws of physics, delivering gifts to all good little children without running out of time or resorting to speeds that would vaporize poor Prancer and Vixen. Naturally, he has an ion shield, operates in 11 dimensions and owns a teleportation device. I confess, however, that I had given little thought to the physics of compiling the naughty list – but was relieved to learn that, as reindeers can see in the ultraviolet end of the spectrum, Santa is probably at least able to spot counterfeit notes and narcotics, which takes care of the most hardened end of child miscreants.

This amusing fact about reindeers’ UV vision crops up as one of many fun asides in physicist Emma Chapman’s effervescent new book First Light: Switching on Stars at the Dawn of Time. The subject of the work is the earliest type of star, rather confusingly dubbed by astronomers as “population III” stars. These giant bodies of helium and hydrogen, consisting of no heavier metals, were several times larger than the Sun and burnt thousands of times brighter. Chapman takes us on a tour of the pursuit of these elusive cosmic antiques, from the basics of star formation and evolution, to what makes population III stars special, all the way to how pioneering astrophysicists are working to locate them today.

Aside from a Magi-like interest in the stars, you may very well be asking: what does the winter holiday season have to do with our universe’s adolescence? You’d be surprised. First Light may be her first book, but Chapman is quite the master of the elaborate structural metaphor, with many of her chapters framed around an overarching anecdote or comparison. Exploring what she dubs the “cosmic dusk” – the ends of the lives of the population III stars – Chapman leads into a discussion of the James Webb Space Telescope by comparing the intricacy of the project to the juggling act of cooking Christmas dinner for one’s extended family (albeit with vastly more stress and more at stake than the Brussels sprouts). Adding to the picture, she deftly compares the James Webb craft’s large, folding mirror to both an origami swan napkin and a Transformers toy one might have found wrapped under a Christmas tree in the 1980s.

The flow is kept firmly tied to the motif by considering the densities of stellar remnants in terms of Christmas turkeys: “The density of a typical white dwarf is about 1000,000,000 kg/m3,” she notes, the equivalent of the unlucky bird “weighing the same as 3000 elephants”. The unexpected presence of supermassive black holes as early as 690 million years after the Big Bang, meanwhile, is like having teenage nieces and nephews turn up for Christmas looking like they have already reached middle age. Whereas the prospect of witnessing the first stellar deaths, or even the earliest stars themselves, would be “like all our Christmases have come at once”. The festive theme is a lovely through-line for the chapter and serves well not only as an explanatory function but also in forging a secondary narrative among what, in the hands of a less-talented writer, could easily have become a stodgy information dump.

An earlier chapter, meanwhile, pulls off the feat of exploring the impact of the first stars on the environment of the early universe by looking at them through the lens of an episode from the geological record: the so-called Great Oxidation Event. Explaining one esoteric scientific concept by first introducing another from a different field would seem like a practice that definitively belongs in the annals of communication no-nos – and yet Chapman makes it work with aplomb. As she explains, this episode, which took place some 2.4–2 billion years ago, saw a revolution in atmospheric make-up as blue-green algae caused the first significant accumulation of free oxygen in the atmosphere. This irreversibly changed the Earth’s environment, causing a mass extinction of existing life, and paving the way for the development of multicellular life. In a similar fashion, the earliest stars overhauled the early universe – adding heavy elements to a mix that had previously only featured hydrogen and helium. Unlike their cyanobacteria analogues, however, population III stars inadvertently brought about their own demise through the changes they wrought.

Emma Chapman’s authenticity and humour shine through

Throughout First Light, Chapman’s authenticity and humour shine through – whether it comes in the form of a darkly funny anecdote about shooting pigeons (which, no matter where they were released, seemed determined to come home to roost in a square horn antenna at New Jersey’s Bell Telephone Laboratory, leaving undesirable “dielectric deposits” on the equipment) or poking fun at elaborate acronyms like WIMPs (weakly interacting massive particles) and MACHOs (massive astrophysical compact halo objects). In fact, my only real criticism of the work is that, while it starts out very well paced, there are a few sections that are a little information-dense, especially in the second half. These seem to cover more material in less space, but even these parts of the work are far more engagingly presented than they might have been at the hands of a lesser writer.

In short, this is a charming book that was as fun to read as it was informative, making it as ideal for the casual reader as for those with an existing understanding of the field.

  • 2020 Bloomsbury Sigma 288pp £15.29hb

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