04宇宙的大尺度结构.pdf

1 星系集团 2星系间的相互作用 第四章宇宙的大尺度结构 1 3星系的演化 (Chapter 24) 本章的教学目标 l掌握星系成团的层次性 l了解星系间相互作用的基本情况 l掌握宇宙的大尺度结构特征 l了解星系的演化* §4.1 星系集团 Galaxies are not distributed uniformly throughout space -- most are evidently held together by gravity due to dark matter between the galaxies. Systems of galaxies Binary galaxies（双重星系 ） Multiple galaxies（多重星系 ） Groups of galaxies（星系群 ） Clusters of galaxies（星系团 ） Superclusters of galaxies（超星系团 ） The larger a given system, the less its density exceeds the mean density of the Universe. 1. The Local Group（本星系群 ） The galaxy cluster includes the Milky Way galaxy, with size of ~1.2 Mpc. There are at least 40 galaxies in the Local Group, three of them are spirals, four irregulars and more than 20 ellipticals. The Milky Way galaxy and Andromeda (M31) are the largest members, and most of the smaller galaxies are gravitationally bound to one or the other of them. Spatial Distribution of the Local Group Spatial Distribution of the Local Group (1) The Magellanic Clouds（麦哲伦云） The Large and Small Magellanic Clouds （大、小麦哲伦云 ） First recorded by F. Magellan in 1519. Physical parameters LMC: D = 50 kpc, M = 2×1010M⊙, d = 10 kpc. SMC: D = 60 kpc, M = 4×109M⊙ , d = 6 kpc. Both are irregular galaxies, orbiting our Milky Way galaxy. Abundant young stars and neutral hydrogen gas. SN1987A occurred in LMC. The Magellanic Stream A 180º long thin stream of neutral hydrogen clouds connecting the Galaxy and the Magellanic clouds. Canis Major Dwarf: A New Closest Galaxy D = 42,000 light years (2) The Andromeda galaxy (M31) The largest galaxy in the Local group, with distance of ~770 kpc and diameter of ~60 kpc. Type Sb spiral galaxy It has seven satellites, all are ellipticals. The Andromeda Galaxy and two of its satellite galaxies, M32 (left) and M110 (bottom right). X-ray Census in Andromeda Supermassive BH X-ray binaries (3) The M33 galaxy The third largest galaxy in the Local Group, with distance of ~720 kpc and diameter of ~18 kpc. Type Sc spir