11/1/18
ASTR 1040: Stars & Galaxies Onward to Galaxies, starting with our own! Our Milky Way Galaxy in overview, aspects of any spiral galaxy – and a fine SONG
• How spiral galaxy may have been assembled • Examine galaxy components: stars, gas, dust • Look at why spiral patterns are made in the disk of galaxies, including our own M51 • Homework #9 due today, new HW #10 out – Whirlpool requires reading S2 on “special relativity”
Prof. Juri Toomre TAs: Ryan Horton, Loren Matilsky • Read Chap 19 “Our Galaxy” in detail, Chap Lecture 20 Thur 1 Nov 2018 20 “Galaxies ..Cosmology” in overview zeus.colorado.edu/astr1040-toomre
OVERVIEW Our Milky Way Galaxy
One-pager: • 100-400 billion stars o Edge-on ALL about us! • ~100,000 light years in diameter, or Sketch ~ 30,000 pc = 30 kpc of Milky Way (kilo-parsecs) o
o • Sun is located about 8.5 kpc from center, Top in the `Orion Arm Artists sketch!
Stars and gas are all moving!
THIS INSPIRES A SONG!
1 11/1/18
If we might see Milky Way from outside
Sing our way to the Milky Way
THE GALAXY -- LIGHTEN UP o Spiral Sb galaxy NGC 4414
Milky Way Anatomy: Spiral Galaxy The Milky Way (fuzzy ribbon of light across the sky) • Disk: includes spiral arms -- young, new star formation
• Bulge & Halo: older stars, globular clusters
Clicker – Where are we? We might prefer to look like this! Prettier? • Why was it so difficult to figure out where in the Milky Way are the Sun and Earth located, and if ours is the only nebula (galaxy) ? • A. We are immersed in a soup of stars, gas and dust, so hard to see far M101 with more • B. In a middle of city of stars, hard to figure D. distinctive shape of overall `metropolitan area spiral arms • C. Gas and dust can absorb light, making distance estimates uncertain • D. All of the above
2 11/1/18
Composite of M101 – much goes on! Disk is very thin! (relatively speaking)
Artist's sketch
Pre-Milky Way: early halo + disk
REAL Galaxy NGC 4565 à nearly edge-on IMAGE!
What are galaxies made of?
How to build a spiral galaxy
(or so we think!)
M104 Sombrero Galaxy
3 11/1/18
Stars Ingredients of Interstellar Very cold Inventory of gas: Medium (ISM) stuff making star birth up our galaxy (stuff between the stars) Gas
Cool gas: neutral H + dark Dust matter Hot H
States of gas in ISM More stuff in ISM Really hot gas inventory
Dust
Now let us look at them in turn ….
Cold Stuff Warm Stuff • Gas & Dust Dark – Heated by stars to 100s-1000s Molecular Kelvin clouds • Absorbs visible and (10’s of Kelvin) UV light
• Transparent to Horsehead longer wavelengths in close-up – Infrared, radio
• Emits its own Horsehead Nebula infrared light
4 11/1/18
Trifid Nebula (M20) Hot Stuff visible Spitzer infrared • Ionization nebulae
• Hot (young) stars ionize hydrogen and other elements in the gas
• T~ 10,000 K near hot young stars
Trifid Nebula
Where the emission colors come from .. Emission nebulae O & B star associations
• Emission lines from hydrogen and other ionized elements
• T~ 10,000 K near hot young stars Lagoon
Really Hot Stuff Fast electrons & magnetic fields REALLY HOT • Bubbles of hot gas STUFF blown out by SUPERNOVAE • Synchrotron • T = millions of emission from degrees K SNR • X-ray and radio • Mixing with rest of galactic gas à • Traces very hot enrichment with gas bubbles heavy elements (SNR)
Cass A SN remnant Flamsteed ~1680 29 Chandra X-ray image of Tycho Brahe 1572 supernova remnant
5 11/1/18
Super-bubbles Super-bubbles in spiral galaxy NGC 3079
• When multiple bubbles join (from a cluster) they can create superbubbles.
• If the superbubbles reaches the edge of the disk, it can blast hot gas out of the Galaxy! – Some will rain back down and mix into the galaxy HST Artist's conception/computer simulations
Clicker Poll of Advice Super-bubbles in Large Magellanic • How do you take notes (or listen) during Cloud (LMC) lectures? (nearby galaxy) • A. I get most of it by just listening • B. I write down some notes, then go back to book to look things up • C. I listen, take some notes, then get copies of lecture slides from course website • D. I enjoy talking with my buddies, and they tell me later if I missed anything • E. I try to read the subject in advance, and then listen, taking some notes in class
Reading ahead clicker – mapping our galaxy • We want to map the structures of very cold gas within the dusty disk of the Milky Way. All spiral galaxies What wavelengths should we be using, are constantly changing and why?
• A. radio A. Cycle of • B. visible light Thestar Starà-Gasgas- • C. x-rays Starà Cyclestar
6 11/1/18
confused visible image A. Radio ISM: • Dust obscures our vision of much of the Reddens the light galaxy in visible and A little DUST UV light. goes a long • X-rays only highlight way! the hottest and weirdest places • 21 cm radio waves Absorbs map normal hydrogen the light gas -- these pass through dust unaffected MW disk in radio
SEMI-WARM stuff: dust
• DUST: absorbs visible and UV light
• Transparent to long wavelengths (red, IR, radio)
• Emits IR light
Horsehead Nebula
7