On Today s s Radar. Reading and Events SECOND MID-TERM EXAM. ASTR 1040 Accel Astro: Stars & Galaxies. Another useful experience (we hope)

Transcription

1 ASTR 1040 Accel Astro: Stars & Galaxies Prof. Juri Toomre TA: Nicholas Nelson Lecture 20 Thur 17 Mar 2011 zeus.colorado.edu/astr1040-toomre toomre Edge-on spiral galaxy NGG 4013 On Today s s Radar Look at why spiral patterns are made in the disk of galaxies, including our own Spiral density waves are traffic jams Interstellar Medium (ISM) gas and dust, plus super-bubbles blown by multiple supernovae Crucial role of cold molecular clouds in starbirth Young O O & B associations stars carve out hot regions: emission nebulae Supernovae make the really hot gas Consider the Gas-Star Star-Gas cycle within the disk Reading and Events Another useful experience (we hope) Overview read Chap 20 Galaxies Read Chap S3 on Spacetime & Gravity (Einstein s s General Relativity) for detailed recitation discussion on Mon March 28 Observatory Night # 6 on Tues March 29 (right after SB) 8:30pm+ (signup) Nick now, Juri in Japan! RESULTS FROM SECOND MID-TERM EXAM SECOND MID-TERM EXAM Grade boundaries,, based on 126 points: Review: One-page story If 110 /126 (87%) or over, A s [37%] 94 /126 (75%) or over, B s [43%] 76 /126 (60%) or over, C s [17%] Also +, plain, and within these ranges Cartoon sketch of Milky Way o Edge-on Go through answer sheet and talk to us if do not understand our choices. Keep exam + answers for future review (comp final) o Top 1

2 REMINDER Inventory of stuff making up our galaxy Stars Gas Why spiral arms? Density waves stars move in and out of denser regions More like ripples in a pond than arms of a pinwheel + dark matter Dust In dense regions, star formation is more intense,, so arms are brighter M51 - Whirlpool Push and pull of gravity in disk Gas/stars are pulled a little forward or backward toward the high density regions Such clumping helps create a spiral pattern Read with care Density wave story how spiral structure is built Stars and gas move through spiral wave Gravitational instability of disks (gentle) Star birth strongly enhanced by shock 2

3 Like Milky Way? Grand design spiral M51 Whirlpool Bright O & B stars mark the spiral pattern NGC 6118 Spiral + SN (VLT) Outlining starbirth in M51 visible infrared Spitzer Q: Why does M51 Whirlpool have open spiral structure, and ours is pretty ragged? A: Collision with companion galaxy enhanced its spiral wave Crash/bang of star birth and recycling: rotating through the spiral arms in the disk M51 Whirlpool Galaxy HST Clicker on deductions about Milky Way s s stars C. Why are stars in the halo poor in the common elements carbon, nitrogen and oxygen? A. Those elements have been used up in halo stars B. C, N and O are biological elements, and there is no life out there to make them C. The halo stars formed before these elements were made in abundance D. Making C, N and O requires massive stars, and these have been absent in the halo 3

4 Ingredients of Interstellar Medium (ISM) (stuff between the stars) Very cold gas: star birth More stuff in ISM inventory Really hot gas Cool gas: neutral H Dust Hot H Now let us look at them in turn. States of gas in ISM ISM Contents: some stuff is HOT Bubbles of hot gas blown out by SUPERNOVAE T = million degree K Mixing with rest of galactic gas enrichment with heavy elements Super-bubbles & Fountains Super-bubble breakout from disk Supernovae can burst hot gas even out of the galaxy! Enriches gas between galaxies Some will rain back down and mix into galaxy Artists conceptions! 4

5 Super-bubbles in Large Magellanic Cloud (LMC) (nearby galaxy) Edge-on view of spiral galaxy NGC 4013 Dust/gas in disk obscures light Plumes and fuzz sticking out are fountains & superbubbles from supernovae HST Super-bubbles in spiral galaxy NGC 3079 ISM is a pretty violent place Life cycle in a molecular cloud HST Fast electrons & magnetic fields Kepler s SNR (1604) latest SN in MW VERY HOT STUFF Synchrotron emission from SNR X-ray and radio Traces very hot gas bubbles (SNR) Chandra X-ray X image of Tycho Brahe 1572 supernova remnant x-ray visible infrared 5

6 Kepler SNR (1604) Chandra X-rayX Really HOT: : Cass A Supernova Remnant Chandra: shock wave + jet Supernova Remnant N49B in LMC Chandra x-ray x images reveal ~one solar mass of magnesium blasted into space by SN Gas & dust heated by stars GAS -- emission lines from hydrogen and other elements (ionization nebulae) T~ 10,000 K near hot young stars T~ 100 K between star forming regions Some stuff is WARM ISM hot gas: Emission nebula (H II region) UV radiation from hot O or B star ionizes a big cavity Emission nebulae O O & B star associations Emission lines from hydrogen and other ionized elements T~ 10,000 K near hot young stars Lagoon 6

7 Where the emission colors come from.. O & B star associations many cluster stars join to blow big bubbles Trifid emission nebula O O & B star associations visible Spitzer infrared 7