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1、3. Matter & Radiation Essentials,Matter Essentials:3. 1. The Big Bang Part 4. Cosmology 3. 2. Dark & Light Matter 3. 3. The Abundances Part 4. Cosmology 3. 4. The Gaseous Universe 3. 5. The Dusty Universe 3. 6. The Cosmic Rays,Radiation Essentials:3. 7. Black Body Radiation 3. 8. Grey Bodies,1,3. 1.
2、 The Big Bang Part 4. Cosmology,Not an event occurred sometime somewhere. Spacetime came into being with the Big Bang.,Redshifts of galaxies The age of the Universe vs. oldest stars: 12.7 13.2 Gyr CMB = Cosmic Microwave Background Abundances of light elements nucleosynthesis in the first moments,2,3
3、. 2. Dark & Light Matter,Most of matter invisible.,3,Evidence for dark matter,Galaxies rotate much faster in their outer regions. extended dark matter surrounding galaxies.Dark matter is needed to bound galaxy clusters.Gravitational lensing Mtotal Mvisible,2 independent pieces of evidence for DM in
4、GCs.,4,3. 3. The Abundances Part 4. Cosmology,The abundance of the elements are quantified by their number fraction or mass fraction:,5,solar (cosmic) abundance,primordial abundance & enrichment,metals: elements other than H and He Z: metallicity,6,Primordial abundances (in the immediate aftermath o
5、f the Big Bang): H, He, D, 3He, & 7Li,Stellar evolution & ISM enrichment Part II. Stars,P-P chain (M1.5Msun) He: the only product,Supernovae & Explosive Nucleosynthesis,M8Msun SNe II elements heavier than Fe Typical kinetic energy 1051 erg,7,Zhou+06,star formation history & IMF,8,Lu, Zhou, Wang et a
6、l. 2006,IMF = Initial Mass Function: The admixture of stars of different masses when first formed.,3. 4. The Gaseous Universe,Metallic-like liquid H at the center of Jupiter,9,H & HeTemperature T Density ne State of ionization,H (n=2),How to know T, ne, and H+/H0 ?,Spitzer (1978): for T8x104K, parti
7、cle encounters are almost always elastic.,thermal timescale hours years astrophysical gases are in thermal equilibrium.,Kinetic temperature & Maxwell-Boltzmann velocity distribution,Gas, energy changed between particles via elastic collisions Statistical mechanics Maxwell-Boltzmann velocity distribu
8、tion kinetic temperature,10,: mean-square particle speed. Root-mean-square (r.m.s) particle speed:,most probable speed:,mean speed:,the ideal gas,An ideal gas is a gas that obeys the ideal gas law (particle pressure):,11,where,is called the mean molecular weight (mi is the mean mass of the ith parti
9、cle), e.g.,mean atomic metal weight: mi=AimH,+ electron degeneracy,Statistical equilibrium, (Local) Thermal Equilibrium=(L)TE,collision excitation/de-excitation absorption excitation/ionization emission de-excitationThe populations of energy levels are determined by including all processes that both
10、 populate & de-populate any given level. In a steady state, the transition rate into any level equals the rate out statistical equilibrium. Equations of statistical equilibrium are set up for each level and involve the density of the particles, the energy density of the radiation field, and coeffici
11、ents describing collisional, radiative, and spontaneous transition probabilities. The coefficients may themselves be functions of other quantities, such as quantum mechanical parameters or temperature. Extremely complex simplification,12,If a gas is in TE, the energy in the radiation field is in equ
12、ilibrium with the kinetic energy of the particles. LTE: a gas has TE properties, but only locally.,Boltzmann Equation,For LTE, the equations of statistical equilibrium are much simplified and the population of states is given by the Boltzmann Equation:,13,Where n is the principle quantum number, Nn
13、is the number of atoms in which electrons are in the nth energy level (e.g., N1 is the number of atoms with electrons in the ground state), gn is the statistical weight (e.g., for hydrogen, gn=2n2), and E is the energy difference between state n and the ground state.,General form of Boltzmann Equati
14、on,Rather than,14,Generally,where, is called the partition function.,e.g., at T3500 K, the partition function for hydrogen reverts to the statistical weight of the ground state, i.e., U=g1exp-0/(kT)=g1=2*12=2.,Ionization & the Saha Eq.,15,3. 5. The Dusty Universe,1. Observational effects of dust,16,
15、M104,extinction:,selective extinction:,e.g.,the ratio of selective to total extinction:,extinction curve of the Milky Way,17,structure, composite, & origin of dust,the size of dusty grains is likely present in a power law distribution:,18,?composite: PAHs=Polycyclic Aromatic Hydrocarbons; SiO2; CH4;
16、 H2O; NH3 etc.,the origin of dust: Cool atmospheres of evolved stars; Metal-rich ejecta of SNe Smoking quasars (Elvis+00)?,3. 6. The Cosmic Rays,Victor Hess (1912): an electrometer discharges more quickly at higher altitudes the source of the discharge must be from above the atmosphere, instead of the earth 1936, Nobel Prize for physics,19,cosmic ray composite:98%: nucleons: H+(87%); He2+(12%); Zz+(1%)2%: e-/+,
