1、天 文 学 概 论A Brief Course of AstronomyAstronomy 4230Lecture 6 The Life of Stars The Life of Stars Throughout their whole history, stars fight an immense struggle between Gravity Pressure Most of the time : Stable Equilibrium Only instable before reaching equilibrium (Birth Process) and after running o
2、ut of fuel (Death)恒星的一生就是一部和引力斗争的历史！Interstellar gas and dust pervade the Galaxy Interstellar gas and dust, which make up the interstellar medium, are concentrated in the disk of the Galaxy Clouds within the interstellar medium are called nebulae Dark nebulae are so dense that they are opaque They a
3、ppear as dark blots against a background of distant stars Emission nebulae, or H II regions, are glowing, ionized clouds of gas Emission nebulae are powered by ultraviolet light that they absorb from nearby hot stars Reflection nebulae are produced when starlight is reflected from dust grains in the
4、 interstellar medium, producing a characteristic bluish glow亮星云： 发射星云 ， 反射星云星云暗星云三叶星云 (Trifid nebula)Angular Momentum Problem The amount of angular momentum (AM) in a typical star forming cloud core is several orders of magnitude too large to be contained in a single star. Two possible ways to dispo
5、se the excess AM AM is transported to outlying diffuse material in an accretion disk. AM goes into orbital motions of the stars in a binary or multiple system.Formation of Massive Stars and Clusters Intense radiation emitted by a massive accreting protostar can produce feedback effects on the infalling envelope that limits continuing accretion. Portostellar interactions (e.g. mergers) may play an important role in formation of massive stars.
