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Stars and their role in providing carbon

Date: 12 July 2020 Tags: Space

Issue

A study has provided new insights on the origins of the carbon in our galaxy. It is an analysis of white dwarfs, the dense remnants of a star after its death.

 

Background

Carbon is essential for life: It is the simple building block of all the complex organic molecules that organisms need. It is known that all the carbon in the Milky Way came from dying stars that ejected the element into their surroundings.

 

Details

  • Most stars, except the most massive ones, are doomed to turn into white dwarfs. When the massive ones die, they go with a spectacular bang known as the supernova.

  • Both low-mass and massive stars eject their ashes into the surroundings before they end their lives. And these ashes contain many different chemical elements, including carbon.

  • Both in low-mass stars and in massive stars carbon is synthesised in their deep and hot interiors through the triple-alpha reaction, that is the fusion of three helium nuclei.

  • In low-mass stars, the newly synthesised carbon is transported to the surface [from the interiors] via gigantic bubbles of gas and from there injected into the cosmos through stellar winds.

  • What astrophysicists debate is whether the carbon in the Milky Way originated from low-mass stars before they became white dwarfs or from the winds of massive stars before they exploded as supernovae. The new research suggests that white dwarfs may shed more light on carbon’s origin in the Milky Way.

  • The researchers analysed a few white dwarfs belonging to open star clusters of the Milky Way. They measured the masses of the white dwarfs, derived their masses at birth, and from there calculated the “initial-final mass relation”, a key astrophysical measure that integrates information of the entire life cycles of stars.

  • In the last phases of their life, stars that were about 2 solar masses produced new carbon atoms in their hot interiors, transported them to the surface, and finally spread them into the interstellar medium through gentle stellar winds.

  • Stars more massive than 2 solar masses, too, contributed to the galactic enrichment of carbon. Stars less massive than 1.65 solar masses did not.

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