Asymptotic giant branch Asymptotic giant branch The asymptotic giant branch (AGB) is a region of the Hertzsprung–Russell diagram populated by evolved cool luminous stars. This is a period of stellar evolution undertaken by all low- to intermediate-mass stars (0.6–10 solar masses) late in their lives. Observationally, an asymptotic-giant-branch star will appear as a bright red giant with a luminosity thousands of times greater than the Sun. Its interior structure is characterized by a central and largely inert core of carbon and oxygen, a shell where helium is undergoing fusion to form carbon (known as helium burning), another shell where hydrogen is undergoing fusion
Power-to-gas produce hydrogen. This microbial power-to-gas reaction occurs at ambient conditions, i.e. room temperature and pH 7, at efficiencies that routinely reach 80-100%. However, methane is formed more slowly than in the Sabatier reaction due to the lower temperatures. A direct conversion of CO to methane has also been postulated, circumventing the need for hydrogen production. Microorganisms involved in the microbial power-to-gas reaction are typically members of the order "Methanobacteriales". Genera that were shown to catalyze this reaction are "Methanobacterium", "Methanobrevibacter", and "Methanothermobacter" (thermophile). The synthetic methane generated from electricity can also be used for generating protein rich feed for cattle,