Scientists Have Found the Source for Cosmic Carbon, One of the Main Building Blocks of Life

Stars, like our Sun, not only provided a crucial environment for life during their lifetimes, it turns out they also provide the main building blocks of life during their death. Approximately 90% of all stars end their lives as white dwarfs while the rest explode as supernovae.

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As they collapse, these stars spread their ashes into the surrounding space through stellar winds enriched with chemical elements, including carbon, an element crucial to all life in the Milky Way and other galaxies.

For a long time now, scientists have known that every carbon atom in the universe was created by stars, through the fusion of three helium nuclei. What they were unsure of is whether this carbon came from white dwarfs or supernovae.

Now, an international team of astronomers that analyzed white dwarfs in open star clusters in the Milky Way based on astronomical observations concluded in a study conducted in 2018 at the W. M. Keck Observatory in Hawaii that white dwarfs are responsible for carbon.

The researchers achieved this by studying the relationship between the initial masses of stars and their final masses as white dwarfs, a relationship known as the initial-final mass relation.

“From the analysis of the observed Keck spectra, it was possible to measure the masses of the white dwarfs. Using the theory of stellar evolution, we were able to trace back to the progenitor stars and derive their masses at birth,” said co-author of the new study Enrico Ramirez-Ruiz, professor of astronomy and astrophysics at UC Santa Cruz.

What they found was that the masses of the newly discovered white dwarfs in old open clusters were notably larger than expected. “Our study interprets this peculiarity in the initial-final mass relationship as the signature of the synthesis of carbon made by low-mass stars in the Milky Way,” said lead author Paola Marigo at the University of Padua in Italy.

The researchers then further found that stars bigger than 2 solar masses also contributed to the galactic enrichment of carbon, while stars of less than 1.5 solar masses did not.

“Now we know that the carbon came from stars with a birth mass of not less than roughly 1.5 solar masses,” concluded Marigo. The study is published in the journal Nature Astronomy.