j. chase Astronomy 10BH Week 6 Ch. 11 Between the Stars: Gas and Dust in Space 11.5 Recycling Cosmic Material • The sun is located at the edge of the low-density cloud called theLocal Fluff • The sun and this cloud are located within theLocal Bubble,a region extending to at least 300 lightyears from the sun • within which the density of interstellar material is extremely low Ch. 13 Stars: From Adolescents to Old Age 13.1 Evolution from the Main Sequence to Giants • When stars first begin nuclear fusion, they lie on thezero-age main sequence • the amount of time a star spends in the main sequence depends on its mass • high mass stars go through evolution more quickly than low mass stars • Nuclear fusion changes stars’ composition • as they age, they evolve into red giants or supergiants • the core of a red giant is contracting, but the outer layers are expanding as a result of fusion—the star gets larger and redder as it expands and cools 13.4 Further Evolution of Stars • After stars become the red giants their cores eventually become hot enough to produce energy by fusing helium to form carbon and oxygen • The fusion of three helium nuclei produces carbon through thetriple-alpha process • helium flashthe rapid onset of helium fusion in the core of a low mass star •
