Astronomers connect white dwarfs as primary source of carbon in the Milky Way

16. July 2020

An international research team has analyzed the carbon content of white dwarfs from galaxy clusters in the Milky Way. The results shed new light on the origin of carbon in our galaxy, which is essential for life on Earth. The international research team includes Enrico Ramirez-Ruiz, who is supported by one of the DNRF’s Niels Bohr Professorships. The study was recently published in the scientific journal Nature Astronomy.

Illustration of a white dwarf surrounded by dust rings.
Illustration of a white dwarf surrounded by dust rings. Credit: NASA’s Goddard Space Flight Center/Scott Wiessinger

Astrophysicists around the world are still debating which types of stars are the primary source of carbon in our galaxy, the Milky Way. Some believe it is due to low-mass stars, while others believe it stems from the carbon synthesis of massive stars that eventually exploded as supernovae. Using data from the W.M.  Keck Observatory in Hawaii, an international team of scientists, including Professor Enrico Ramirez-Ruiz, who holds one of the DNRF’s Niels Bohr Professorships, analyzed the carbon content of white dwarfs from five open star clusters in the universe.

”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 Professor Ramirez-Ruiz.

The relationship between the stars’ initial masses and their final masses as white dwarfs is a fundamental observation in astrophysics, as it integrates information from the entire life cycle of stars. The analysis of the white dwarfs surprisingly showed that the masses were bigger than expected, which created a kind of “crack” in the observations for the initial and final mass ratio, respectively.

By analyzing the two mass ratios at the time the crack occurred, the researchers were able to conclude that stars with larger masses contributed to the galactic enrichment of carbon, while stars with a smaller mass did not.

“These results place stringent constraints on how and when carbon, the component important to life on Earth, was developed by the stars of our galaxy, sooner or later ending up trapped in the raw materials from which the sun and its planetary network were fashioned 4.6 billion years ago, a long time back,” said Professor Ramirez-Ruiz.

Read the scientific article “Carbon star formation as seen through the non-monotonic initial–final mass relation” in Nature Astronomy here

You can find more information about the study from Professor Enrico Ramirez-Ruiz and the rest of the research team here