Carbon stars, predominantly red giants or seldom red dwarfs, are distinguished by their exceedingly low surface temperatures and an atmospheric carbon surplus. Contrasting regular red giants where oxygen outnumbers carbon, these stars undergo a unique phase in stellar evolution termed as the AGB phase.
When a star depletes its hydrogen reserves, helium burning ensues in the core through the triple-alpha reaction. This process yields carbon, thus escalating its abundance in the star's atmosphere. The low surface gravity of carbon stars further aids in the expulsion of carbon and its compounds into space, forming disks of dust and gas rich in carbon and its derivatives.
An intriguing example of a carbon star is CW Leonis. Situated a mere 310 light-years away in the Leo constellation, it is the closest carbon star to Earth. The Hubble Telescope's detailed imagery reveals the typical characteristics of carbon stars, including the circumstellar disk.
However, the complex structure of CW Leonis, with its intersecting arcs and shells, has left astronomers perplexed. The mechanisms leading to this intricate formation remain an unsolved mystery in the field of astrophysics.
Image Credits: ESA, NASA, Hubble, T. Ueta (U. Denver), H. Kim (KASI).
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