Made of stars: how the universe forged the elements in your body

The atoms in your body were assembled in at least three stages. The particles survived a contest between matter and antimatter just after the Big Bang. The Big Bang left only hydrogen, helium and a trace of lithium. Everything heavier was made later, in stars up to iron and, for the heaviest elements, mostly in events such as colliding neutron stars. Three scientists who study different stages tell a story that fits together.

Harry Cliff, a particle physicist at Cambridge, starts earliest. Every atom is made of just three particles: electrons, up quarks and down quarks, each a ripple in a field that fills all of space. The puzzle is why they exist. The Big Bang should have made equal amounts of matter and antimatter, which would have wiped each other out and left a universe black and empty apart from some photons. Only one in a billion particles survived. "You and I are leftovers," he says. The explanations are candidates, and he says there is no clear evidence yet for any of them.

Anna Frebel, an MIT astronomer who studies the oldest stars, gives the chemical history. The first stars were around 100 times the mass of the Sun and exploded within a few million years, seeding the universe with its first carbon, oxygen, magnesium and iron. Enrichment has gone only one way since; by the time the Sun formed, the gas had been enriched by roughly a thousand generations of supernovae. Elements heavier than iron mostly come from the rapid neutron-capture process, and in 2017 a detected neutron star merger confirmed mergers as one site of it.

Michelle Thaller, an astrophysicist and retired NASA executive, brings it home. The iron, oxygen, carbon and phosphorus in our bodies were made in stars, so "astrophysics is the story of, you know, the end of your nose, literally." Dying stars pour out carbon, which readily builds organic chemistry in space. Her evidence is the sample returned from the asteroid Bennu, which contained all the nucleobases of both DNA and RNA.

They agree that ordinary matter has a traceable history billions of years long. One statement does not match. Thaller says the interior of a star is the only place that makes atoms, while Frebel separates the Big Bang's light elements, fusion up to iron, and neutron capture beyond it. The difference is precision more than substance. On Frebel's account, the hydrogen in your body is older than any star.

The reason anyone can say this is spectroscopy. Each element leaves its own fingerprint in starlight split into colors, and a small old star's surface keeps the composition of the gas it was born from.

There are limits. The sources do not say mergers are the only source of the heaviest elements, none gives proportions for a human body, and building blocks on an asteroid show the ingredients are delivered, not how life began.

What to do with it: drop the picture of electrons orbiting like tiny planets. When you say we are made of stars, add that hydrogen and helium come from the Big Bang. Sort elements by origin. When someone claims to know what a star is made of, ask for the spectrum. And keep the open question open: why matter outlasted antimatter is still unexplained.