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Binary stars boost cosmic carbon footprint

Christian Fernsby |
The cosmic origin of carbon, a fundamental building block of life, is still uncertain.

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Massive stars play an important role in the synthesis of all heavy elements, from carbon and oxygen to iron and so on.

But even though most massive stars are born in multiple systems, the nucleosynthesis models so far have almost exclusively simulated single stars. An international team of astrophysicists has now calculated the "carbon footprint" of massive stars that lose their envelope in a binary system.

Most stars, including our own star the Sun, are powered by fusing hydrogen into helium. In their 'golden years," after completing about 90% of their life, they start converting helium to carbon and oxygen.

Stars like the Sun stop here, but massive stars can continue to fuse carbon into heavier elements up to iron.

The big challenge is not how to produce carbon, but how to get it out of the star, before it is destroyed.

In single stars this is very hard. Stars in binary systems can interact and transfer mass to a companion. The star that is losing parts of its mass develops a carbon-rich layer close to the surface, which is ejected when the star explodes as a supernova.

Astronomers are also investigating other types of stars that can produce carbon, such as for example, red giant stars or explosions of white dwarf stars. But so far it seems that massive stars, and according to this new study binary stars in particular, make the majority of the cosmic carbon.

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