Where did the carbon in our bodies and the oxygen we breathe come from?
Astronomers have been asking this question for decades, and a new study from Leiden University brings us closer to the answer by looking at nearby stars in a completely new way.
In research published today in Nature Astronomy, scientists report the first-ever detection of rare forms of carbon and oxygen—known as isotopes—in stars close to our Sun.
These measurements offer fresh clues about how the universe gradually built up the elements that make life possible.
Shortly after the Big Bang, the universe was a very simple place. It contained mostly hydrogen and helium, with none of the heavier elements we now depend on.
Carbon and oxygen did not yet exist. They were created much later inside stars, where extreme heat and pressure allow nuclear fusion to turn lighter elements into heavier ones.
But fusion is only the beginning of the story. When stars age and die, they release the elements they have made back into space.
Some stars gently shed their outer layers, while others explode as supernovae. This material then mixes into the gas of the Milky Way, becoming the raw ingredients for new stars, planets, and eventually worlds like Earth. In this way, the universe constantly recycles its matter.
Every star carries a chemical record of this long history. The research team, led by Darío González Picos, found a new way to read that record by studying isotopes. Isotopes are slightly different versions of the same element.
For example, all carbon atoms have six protons, but some have six neutrons while others have seven. On Earth, almost all carbon has six neutrons, while the seven-neutron version is rare.
Using extremely detailed measurements of starlight, the team was able to measure the ratios of these rare isotopes of carbon and oxygen in 32 nearby stars with unprecedented accuracy. They discovered that stars with fewer heavy elements overall also contain fewer of these rare isotopes.
This result fits neatly with predictions from models of how the Milky Way evolved chemically over time.
It also gives astronomers a powerful new tool. By measuring isotope ratios, they can effectively “rewind the clock” and estimate how enriched the galaxy was when a star formed.
One surprising aspect of the study is where the data came from. All the observations were taken years ago by the Canada France Hawaii Telescope and stored in its archives. They were originally collected to search for planets around other stars, not to study isotopes. González Picos realized that these high-quality spectra could be reused in a completely different way—and it worked.
In the end, this research is about more than distant stars. By tracing the origins of carbon and oxygen, astronomers are uncovering the deep cosmic history that led to our own existence, and helping us understand how Earth became a place where life could arise.
