Carbon Star

Red giantGiant and highly luminous red star in the later stages of stellar evolution after it has left the main sequence. These red stars have a relatively cool surface whose core has burned most of its hydrogen. Red giants lose parts of their atmospheres and thus provide new elements into interstellar (or occasionally red dwarf) starSelf-luminous object held together by its own self-gravity. Often refers to those objects which generate energy from nuclear reactions occurring at their cores, but may also be applied to stellar remnants such as neutron stars. whose atmosphere contains more carbonElement commonly found in meteorites, it occurs in several structural forms (polymorphs). All polymorphs are shown to the left with * indicating that it been found in meteorites and impact structures: a. diamond*; b. graphite*; c. lonsdalite*; d. buckminsterfullerene* (C60); e. C540; f. C70; g. amorphous carbon; h. carbon nanotube*. than oxygenElement that makes up 20.95 vol. % of the Earth's atmosphere at ground level, 89 wt. % of seawater and 46.6 wt. % (94 vol. %) of Earth's crust. It appears to be the third most abundant element in the universe (after H and He), but has an abundance only, which combine in the outer layers of the star, forming carbon monoxideMolecule (CO) used to map the distribution of matter, especially molecular hydrogen, H2, in interstellar space. Molecular hydrogen is by far the dominant molecule in molecular clouds, but is very difficult to detect. One reason is that the strength of spectral lines from molecules is related to how asymmetric the and other carbon compounds. The abundance of carbon is thought to be a product of heliumHelium (He) Second lightest and second most abundant element (after Hydrogen) in the universe. The most abundant isotope is He (99.9998%), He is very rare. Helium comprises ~8% of the atoms (25% of the mass) of all directly observed matter in the universe. Helium is produced by hydrogen burning inside fusionProcess in which two lighter atomic nuclei combine to form a heavier atomic nucleus. Very high temperatures are normally required in order for atomic nuclei to collide with sufficient energy to overcome the Coulomb barrier (their mutual electrostatic repulsions). Fusion that occurs under high-temperature conditions is called thermonuclear fusion. Fusion within the star. Carbon stars are cool (2000-3000 K), deep red or brown colored, and emit most of their energy at IR wavelengths (shorted wavelengths are absorbed by atmospheric carbon). Although very large, carbon stars are difficult to detect without specialized equipment. All carbon stars are irregular or semiregular variable stars.

Many carbon stars are actually binary stars, where one star is a giant star and the other a white dwarfRemnant of a star with mass <8 Msun. White dwarfs have masses <1.4 Msun (the Chandrasekhar mass) and are supported by electron degeneracy pressure. White dwarfs have radii ~Rearth (<0.02 Rsun) and densities ~105-6 g/cm3. No nuclear fusion or gravitational contraction occurs in white dwarfs, they shine by residual heat.. The giant star loses carbon to the surface of the white dwarf, resulting in a carbon enhanced spectra. Many carbon compounds (HCN, C2N2), Li, and Zr have been detected at high levels, which have circulated from the coreIn the context of planetary formation, the core is the central region of a large differentiated asteroid, planet or moon and made up of denser materials than the surrounding mantle and crust. For example, the cores of the Earth, the terrestrial planets and differentiated asteroids are rich in metallic iron-nickel. of the star into its upper layers.

As much as half (or more) of the total mass of a carbon star may be lost in powerful stellar winds that eject carbon-rich “dust” into the interstellar mediumMaterial between the stars, consisting of gas, dust and cosmic rays (high energy charged particles moving at nearly the speed of light). It comprises ~10% of visible matter in the disk of our Galaxy (Milky Way). Until recently it was generally assumed that silicates in the ISM were amorphous, but. This dust provides the raw materials for the creation of subsequent generations of stars. The ablated material surrounding a carbon star may blanket it to the extent that the dust absorbs all visible light.