AY 101 Chapter Notes - Chapter 13: Planetary Nebula, Brown Dwarf, White Dwarf
15 Jul 2016
School
Department
Course
Professor
Document Summary
In this chapter, we have seen how the origin of the elements, rst discussed in chapter 1, is linked to the lives and deaths of stars. As you look back, keep in mind these big picture ideas: virtually all elements in the universe besides hydrogen and helium were forged in stars. How do stars form: stars are born in cold, relatively dense molecular clouds. As a cloud fragment collapses under gravity, it becomes a rapidly rotating protostar surrounded by a spinning disk of gas in which planets may form. The protostar may also re jets of matter outward along its poles. How massive are newborn stars: on the upper end, the most massive newborn stars are about 150msun. On the lower end, stars cannot be less massive than 0. 08msun; below this mass, degeneracy pressure prevents gravity from making the core hot enough for ef cient hydrogen fusion, and the object becomes a brown dwarf.
