Transcript Document
Galactic coordinates in celestial equator plane NCP in galactic plane galactic equator tilted ~ 63 1/2 deg to CE galactic center is toward Sagitarrius RA~18h, Dec ~ -29deg Makeup of Milky Way Galaxy Stars - Disk (O, B stars, SG, young to old open clusters) Halo & Bulge (RR Lyr, globular clusters, MACHOs) Gas - some in disk, hot gas in halo Dust - in disk [results in reddening E(B-V), Av] DUST m-M = -5 + 5 log d + A E(B-V) = (B-V)observed - (B-V)normal Av ~ 3 E(B-V) [~ 1 mag/kpc roughly] Find E(B-V) from: • spectral type of star and observed B-V • H / H ratio [normal = 3] • HI maps NH/E(B-V) = 5x1021 atoms/cm2/mag • 2200Å bump 0 Extinction = 10 A()/E(B-V) 4 0 0 0 0 0 Wavelength (Å) 0 Stellar Populations z(pc) Age (109yrs) Z Distr Extreme Pop I 120 <0.1 0.04 patchy Older Pop I 160 0.1-10 0.03 patchy Examples O,B,SG, open clusters sun, A stars ************************************************************************************* Disk Pop II 400 3-10 0.02 smooth planetaries, RR Lyr Intermed Pop II 700 10 0.01 smooth long P var Halo Pop II 2000 >10 0.003 smooth globular clusters Interstellar Gas • optical absorption lines CaI, CaII, NaI • HII regions (recombination around hot star) T~10,000K, density ~ 5000 ions/m3 • HI gas (21 cm) T~100K, density ~106 atoms/m3 • molecular clouds (radio) H2, OH, NH3 T~10K, density ~109 mol/m3 • X-rays (hot coronal gas) T~ 106K, density < 104 particles/m3 Counting Stars D= #stars/unit volume Local luminosity function: #stars/unit V with given Mv total sky = 4 steradians = 41,253 sq deg for solid angle , area = r2 dV = r2 dr dr N(r) = D(r)dV= Dr2dr = 1/3 Dr3 log r = (m-M+5)/5 = 0.2 m + const (for given M) r = 10(0.2m+c) and N(r) = 10(0.6m+c) since 100.6 = 4, expect 4xmore at m+1 than m not observed r r2 Finding the mass of the Milky Way Kepler’s law using sun’s orbit (P=250 million yrs, v=250 km/s, a=8kpc) mMW + msun = 42a3/GP2 ~ 1011M Halo mass: MACHOs, high vel stars Rotation curve: M = rv2/G The Galactic Center (Sgr A*) Evidence for a Supermassive BH at the center: • stationary (located at dynamic center of MW) • energetic X-ray source • small size (radio shows smaller than solar system) • no visible object at opt nor IR from Keck images • motions of nearby stars (1000’s of km/s) imply 3 million M How does Supermassive BH form? • stars in center are < 1000AU apart (200,000AU near sun) • SN chain reaction could produce many stellar BHs • collisions between BHs cause monster supermassive BH Galaxy Evolution • Top Down: large concentration of matter (1015M) fragment into galaxies of 1012M • Bottom up: small structures merge into galaxies, then clusters 1) globulars formed ~ 13 billion yrs ago 2) collapse to disk 3) star formation continued in disk 4) collisions with dwarf galaxies add to halo 5) in ~ 5 billion yrs, collision with Andromeda could cause burst of star formation, uses up gas & dust and turns MW into an elliptical galaxy Review of Astr 322- the Contents of the Milky Way Content Structure Disk Bulge Stars Gas & Dust Hot, cold; Av, E(B-V) Dark Matter MACHOs + ? Pop I Halo Pop II Pop II Motion Disk - LSR Halo - high v, elliptical Single (sun), binary, clusters (open, globular) Viewing geometry Properties (d, T, L, Mv, spectra, mass, radius) Horizon (alt, azimuth) Celestial (RA, Dec) Galactice (b, l) Evolution - low mass (T Tauri, MS, giant, planetary, WD) - high mass (MS, SG, SN, pulsar or BH) Variables - geometric, eruptive, pulsating Instrumentation: Telescopes (refractors, reflectors) CCDs, spectrographs, Space