Where Does Carbon Come From?

Where Does Carbon Come From?

In the course of their lives, like celestial chemical factories, stars are fusing hydrogen and helium atoms to form progressively heavier elementsincluding carbon. In death, extremely massive stars explode. Near the end of its nuclear explosion, stars expel most of its outer material, creating a planetary nebula while releasing their chemical creations into space via stellar winds.

A recent study published in Nature Astronomy carries an explanation on carbon’s origin in the Milky Way as they examined dying stars, called white dwarfs. 

A white dwarf is basically the stellar core remnant after the star has exhausted its nuclear fuel.

“The findings pose new, stringent constraints on how and when carbon was produced by stars of our galaxy, ending up within the raw material from which the Sun and its planetary system were formed 4.6 billion years ago,” says the author of the paper, Jeffrey Cummings, a Research Scientist in the Johns Hopkins University’s Department of Physics & Astronomy.

As carbon is an essential element to life on Earth, scientists have been seeking out its origin. This study provides crucial evidence that may help astrophysicists solve the longstanding mystery of where the carbon in the Milky Way Galaxy came from.

Through data collected between August and September 2018 from the Keck Observatory, researchers offer valuable insights into the activity of white dwarfs belonging to the Milky Way’s open star clusters. Open star clusters are groups of stars that are held together by mutual gravitational attraction. 

The white dwarfs’ current masses were measured and under the theory of stellar evolution, they were able also to determine their birth masses. The results were put into an initial-final mass relation in order to determine the entire life cycles of the stars. When Cummings and his colleagues calculated the relation, they discovered that the white dwarfs they analyzed had larger masses than it was expected. Other studies always found an increasing linear relationship before, as in the more massive the star was at birth, the more massive the white dwarf would be. 

They apparently managed to break the linear trend as they discovered that stars born about 1 billion years ago did not produce white dwarfs of 0.60-0.65 solar masses, as it was presumed; they actually produced more massive remnants of about 0.7—0.75 solar masses.

Scientists believe that this discovery holds the explanation of how carbon from low-mass stars entered the Milky Way. Near the end of their death, stars produced new carbon atoms and released them into the cosmos. The carbon atoms spread into the surrounding interstellar spaces via stellar winds.

The research team explained that the stripping of the carbon-rich outer mantle appeared at a slow pace – creating a convenient situation for the cores to grow significantly in mass. They claim that solar masses had to be at least 1.5 for the carbon to be expelled.


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