《哈工大天文学概论第一节1讲解》由会员分享，可在线阅读，更多相关《哈工大天文学概论第一节1讲解（126页珍藏版）》请在金锄头文库上搜索。
1、天 文 学 概 论 A Brief Course of Astronomy Astronomy 4230 Lecture 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 runnin
2、g out 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
3、They appear 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
4、in the 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
5、to dispose 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 t
6、he infalling envelope that limits continuing accretion. Portostellar interactions (e.g. mergers) may play an important role in formation of massive stars. 褐矮星 (Brown Dwarfs) Failed Stars Masses 0.08 M(10MJ- 84 MJ) Central temperature 3 million K Surface temperature 1000 K Differences between brown d
7、warfs and planets Planets are smaller and lighter Planets have a solid core They are formed in a complete different way 气体云的收缩 原恒星 主序前星 零龄主序 零龄主序 云块碎裂、辐射 M MC MC3-6 M 主序星的演化 主序星的性质 均匀的化学组成 核心H燃烧 质量范围: 0.08 M 10M)恒星的演化 观测表现 ： O型星蓝超巨星黄超巨星红超巨星超新星 恒星内部物理过程 ： 核心H枯竭壳层H燃烧 核心He燃烧核心He 枯竭 壳层He和H燃烧 核心C燃烧核心C枯 竭
8、 壳层C、He和H燃烧 O, Ne, Si燃烧 Fe核 Sequence of Events in a Supernova Explosion 核反应停止，核坍缩 R cTc Fe核光致离解 4He光致离解 e- + p n + ne 电子数目、能量损失 Pe R cTc, 星核坍缩 当rc = rnu，中子简并 核坍缩停止，中子星 外部下落物质激波反弹 壳层抛射 II型超新星爆发 Evolutionary Stages of a 25 M Star Stage Temperature (K) Density (g/cm3) Duration of stage Hydrogen burning
9、 4 107 5 7 106 years Helium burning 2 108 700 5 105years Carbon burning 6 108 2 105 600 years Neon burning 1.2 109 4 106 1 year Oxygen burning 1.5 109 107 6 months Silicon burning 2.7 109 3 107 1 day Core collapse 5.4 109 3 109 1/4 second Core bounce 2.3 1010 4 1014 milliseconds Explosion about 109
10、varies 10 seconds 4. 特大质量恒星的演化 星风引起的质量损失 高光度恒星通常有很强的星 风10-6-10-4 Myr-1 如沃尔夫-拉叶(WR)星。 演化过程 O型星蓝超巨星（红超巨 星）WR星Ib/Ic型超新星 中子星/黑洞 Nebula M1-67 around star WR124 恒星初始质量 (M)演化结局 M 0.01行星 0.01 M 0.08褐矮星 0.08 M 0.25He白矮星 0.25 M 8CO白矮星 8 M 12 (?)ONeMg白矮星 12 M 25 (?)超新星黑洞 不同初始质量恒星的演化结局 超新星 (Supernovae) 和超新星遗迹 (
11、Supernova Remnants) II/Ib/Ic型超新星高质量恒星在演化末态发生的剧 烈爆炸。 星系M 51中的SN 1991T 特征： 光度L107-1010 L， Lf /Li 108 爆发能E1047-1052 ergs（其 中中微子占99% ，动能占 1% ，可见光辐射占0.01%） 膨胀速度v103-104 kms-1 产物： 膨胀气壳（超新星遗迹）+ 致密天体（中子星或黑洞） SN 1998aq in the galaxy NGC 3982 Crab Nebula Remnant of Supernova in 1054 AD 观测分类： I型与II型超新星 谱线特征：I型
12、(Ia, Ib/Ic)无H线，II 型有H线 光变曲线不同 * Optical Spectra and Light Curves of Supernovae 爆发机制： Ia超新星爆发：双星系统中吸积白矮星的C爆轰。 Ib/Ic, II型超新星爆发：大质量恒星的核坍缩。 * 环状星云的结构 Interaction of the Supernova Ejecta with the Inner Ring Optical, Feb. 2000 Radio, Sep. 1999 X-ray, Oct. 1999 X-ray, Jan. 2000 超新星遗迹 (Supernova Remnants) 超
13、新星爆发抛出的大量物质在向外膨胀过程中 与星际物质和磁场相互作用而形成的气体星云 。 强射电辐射和高能辐射源（同步加速辐射，激 波加热）。 年龄 105 yr 形态分类： 壳层型（辐射主要来自纤维状的球形壳层和星 际气体的相互作用）。 混合型（辐射来自遗迹整个区域，并且由中心 的致密星提供能源）。 Crab Nebula - Optical and X-ray 典型的超新星遗迹 Tycho Nebula 天鹅圈 Cygnus Loop Puppies A 典型的超新星遗迹 Cas A The Cycle of Stellar Evolution The Henize 206 nebula N11 Lecture 7 Compact Objects 白矮星 (White Dwarfs) 1. 发现 天狼星（Sirius）双星，Porb= 50 yr 天狼A：mv =1.45m，Mv = 1.4m 天狼B：mv = 8.68m，Mv = 11.6m Sirius in optical and X-ray r = 3.8106 gcm-3 轨道运动 M = 1.05 M Teff = 2.6104 K R5108 cm 结构： 质量M 0.2-1.1 M（平 均 0.6 M
