Preface

This book tells a story which, until some seventy years ago, seemed to belong to philosophical speculation rather than to science: the origin of the chemical elements that make up the world. We now possess a coherent reconstruction of that origin — incomplete, yet robust enough to constitute an autonomous discipline — interweaving nuclear physics, stellar evolution, observational cosmology and isotopic geochemistry. What Eddington [Eddington 1920] could only conjecture a century ago, and what the B²FH paper [Burbidge et al. 1957] systematized at the middle of the twentieth century, has grown into a building still under construction, held up by laboratory measurements, spectroscopic observations, numerical simulations and, in the last few years, by the faint hum of gravitational waves.

Scope of the work

The aim is to present stellar nucleosynthesis as an organic set of processes, from the primordial synthesis of the lightest nuclei to the reactions which, in the final minutes of massive stars or in the mergers of neutron stars, generate the heaviest elements of the periodic table. Where possible I have tried to show not only the results, but also the reasons behind historical and modelling choices: the discipline is young enough that many questions remain open, and the boundary between what is known and what is conjectured deserves to be drawn explicitly.

This is neither an operational handbook nor an exhaustive review. For technical depth I refer the reader to the classical monographs by Clayton [Clayton 1983], Arnett [Arnett 1996], Pagel [Pagel 2009] and Iliadis [Iliadis 2015], and to the review articles cited in each chapter.

Audience and progressive depth

The book is intended for a varied readership: undergraduate and beginning graduate students in physics and astronomy; researchers from adjacent disciplines — chemistry, geology, planetary science — who wish to approach the field; informed readers with a solid general scientific background. To accommodate these different needs, each chapter adopts a progressive-depth style: the treatment moves from accessible narrative — concrete images, everyday analogies and orders of magnitude — toward formalism, quantitative details and the current research frontier.

The levels of difficulty are not visibly separated into blocks. They are woven into the prose so that the reader can follow the argument as far as interest and preparation allow. It is not necessary to read every formula in order to understand the narrative, but every formula is present for readers who want the quantitative structure behind the words.

Prerequisites

To follow the narrative thread of each chapter, curiosity and a school-level acquaintance with the periodic table and the Solar System are enough. To appreciate the derivations and essential formalism, it is useful to know classical mechanics and thermodynamics, the basics of quantum mechanics (tunneling, statistical distributions), and the essentials of nuclear physics (binding energy, $\alpha$ and $\beta$ decay). To follow the most technical details — cross sections, simulation codes, recent literature and open quantitative problems — familiarity with nuclear reaction theory, stellar evolution codes and specialized research articles is recommended.

Notational conventions

Unless otherwise noted, I follow the conventions of the astrophysical literature.

• Units. Gaussian CGS for astrophysical quantities (density in $\mathrm{g\,cm^{-3}}$, energy in erg, cross section in $\mathrm{cm^2}$) and SI or nuclear units when more natural (energies in MeV, cross sections in barn = $10^{-24}\,\mathrm{cm^{2}}$, masses in u or $\mathrm{MeV}/c^{2}$). Relevant conversions are recalled at first occurrence.
• Isotopes. The full notation is $^{A}_{Z}\mathrm{X}$ with mass number $A$, atomic number $Z$, chemical symbol $\mathrm{X}$; where $Z$ is redundant I simply write $^{A}\mathrm{X}$ (e.g. $^{12}\mathrm{C}$, $^{56}\mathrm{Fe}$). For decays I use the standard arrow notation, e.g. $^{14}\mathrm{C} \to {}^{14}\mathrm{N} + e^{-} + \bar{\nu}_{e}$.
• Reactions. Bethe’s compact notation $A(a,b)B$ for $a + A \to b + B$.
• Abundances. Mass fraction $X_{i}$ (with $\sum_{i} X_{i} = 1$), number fraction $Y_{i} = X_{i}/A_{i}$, spectroscopic abundance $\log \epsilon(\mathrm{X}) = \log(N_{\mathrm{X}}/N_{\mathrm{H}}) + 12$. For reference solar abundances I adopt the values of Asplund et al. [Asplund et al. 2021] , flagging departures from earlier compilations when relevant.
• Metallicity. $[\mathrm{Fe/H}] = \log(N_{\mathrm{Fe}}/N_{\mathrm{H}})_{\star} - \log(N_{\mathrm{Fe}}/N_{\mathrm{H}})_{\odot}$.
• Physical constants. Updated CODATA values, collected in the appendix where needed.
• References. Citations use the <Fonte /> component, whose id matches the entries in the bibliography.

Status of the work and contributions

This work is an active draft: chapters and appendices will be updated over time, and the version number in the metadata signals the extent of revisions. The CC BY-SA 4.0 license permits free redistribution and adaptation under the same terms. The source code is public: any report of error — formulae, references, historical lapses, translations — is most welcome.

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Happy reading.

Carlo De Carolis