Ch 15: Smooth Way Cosmic system.

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Ch 15: Smooth Way System Smooth Way = "By means of Lactea"  traverses numerous star groupings Crosses the entire sky in an "extraordinary circle"  Our perspective, from within, of our cosmic system. All Sky SH NH (1) Optical/Infrared/Radio Optical: dust vital IR and radio: genuine evenness uncovered
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Ch 15: Milky Way Galaxy Milky Way = “Via Lactea”  compasses numerous heavenly bodies Crosses the entire sky in a “great circle”  Our perspective, from within, of our cosmic system. All Sky SH NH

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(1) Optical/Infrared/Radio Optical: dust essential IR & radio: genuine evenness uncovered Optical + sub-atomic (CO) All Sky Optical Near Infrared: stars Far Infrared: warm clean Hydrogen 21cm

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(2) External View Galaxy Anatomy : Disk with arms + ISM + youthful “open” bunches Bulge with little bar Nucleus @ extremely focus Halo w. old “globular” bunches 8 kpc = 25,000 l-yr Sun

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(3) History: Slow Discovery ~1610 Galileo: telescope  MW = numerous weak stars ~1750 Herschel(s): number stars  little plate, sun @ focus Sun ~1900 Kapteyn: rehashes & enhances star checks  10 kpc circle, sun @ focus However, issue with star tallies: dust anticipates clear view Need tracer for cosmic system outside dusty MW plane…..

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(3b) ~1920 Shapley Studied appropriation of globular groups Used variable stars to get separations (see later)  bigger framework sun not at focus in Sagittarius Basically adjust (however 3 x too huge; graph named accurately)

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(4) Star Motions Disk : gas & stars in roundabout movement V circle (sun) = 220 km/s  P sphere (sun) = 2 x 10 8 yr = 0.2 Gyr ~ 50 circles since development  ~ 50 “years old” Bulge & radiance stars & GCs : on “ irregular ” circles (scope of oval shapes, numerous slants & headings)

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(4b) Rotation Curve & Galaxy Mass V decay generally steady @ 200-250 km/s  differential revolution (inward stars “overtake” external ones) Mass : a 3/P 2 ~ M ~ 10 11 M sun inside sun Note : as R ↑ M ↑ even past the obvious edge !  Dark Matter is significant part , M DM ~ 10 x M stars “edge” All mass inside

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(5) Star Populations City similitude: distinctive age gatherings live in better places; move in an unexpected way; made of diverse materials (!) curved Metal Rich (solid lines) Metal Poor (feeble lines)

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(6) Galaxy History Simple picture from populaces (1960s) Large, ~spherical, gas cloud  corona stars Collapse , levels, twists up  circle (c.f. procedure of star/planet arrangement) More confirmation (1990s) entangles: i nfall of littler cosmic systems critical annihilated & add to corona & thicken circle Gradual substance enhancement from stellar nucleosynthesis continuous star ↔ gas cycle in slim plate

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(7) Spiral Arms In different universes: arms = locales of star development OB star bunches; DMCs; HII districts Difficult to guide in our world: OB stars & DMCs  close-by arms worldwide example not (yet) conceivable M51

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(7b) Spiral Arm Origin Not straightforward windup  too tight Self-spreading star development + differential pivot  worn out arms “ hairy ” spirals

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(7c) Density Waves circle swarming makes a winding example in plate thickness  moves gradually around stars & gas travel through arm gas compacted  structures stars thickness wave activated/kept up by passing neighbor/focal bar  solid arms  great configuration spirals

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Infrared MW plane (8) Galaxy Nucleus great characterized: < 1pc area (= bacterium on 8 ½ x 11 sheet) Very hard to watch 8 kpc away, behind dust/gas use IR & radio to infiltrate dust Optical

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(8b) Galaxy Nucleus Very high star thickness: ~10 6 stars/pc 3 Much star arrangement & related supernova remainders Anomalous radio source: Sgr A * to a great degree little: < sun based sys size @ focal point of star crest IR Radio

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(8c) Nuclear Black Hole Study circles of stars close Sgr A * (utilizing IR camera) Keplerian ovals & speeds  “point” mass at Sgr A * circles give mass  2.8 x 10 6 M sun Star S2 ways to deal with 80AU move

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