11/1/18. Our Milky Way Galaxy THIS INSPIRES A SONG! Onward to Galaxies, starting with our own! Stars and gas are all moving!

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1 ASTR 1040: Stars & Galaxies Prf. Juri Tmre TAs: Ryan Hrtn, Lren Matilsky Lecture 20 Thur 1 Nv 2018 zeus.clrad.edu/astr1040-tmre M51 Whirlpl Onward t Galaxies, starting with ur wn! Our Milky Way Galaxy in verview, aspects f any spiral galaxy and a fine SONG Hw spiral galaxy may have been assembled Examine galaxy cmpnents: stars, gas, dust Lk at why spiral patterns are made in the disk f galaxies, including ur wn Hmewrk #9 due tday, new HW #10 ut requires reading S2 n special relativity Read Chap 19 Our Galaxy in detail, Chap 20 Galaxies..Csmlgy in verview OVERVIEW Our Milky Way Galaxy billin stars ~100,000 light years in diameter, r ~ 30,000 pc = 30 kpc (kil-parsecs) One-pager: ALL abut us! Sketch f Milky Way Edge-n Sun is lcated abut 8.5 kpc frm center, in the `Orin Arm Artist s sketch! Tp Stars and gas are all mving! THIS INSPIRES A SONG! 1

2 If we might see Milky Way frm utside Sing ur way t the Milky Way THE GALAXY -- LIGHTEN UP Spiral Sb galaxy NGC 4414 Milky Way Anatmy: Spiral Galaxy Disk: includes spiral arms -- yung, new star frmatin The Milky Way (fuzzy ribbn f light acrss the sky) Bulge & Hal: lder stars, glbular clusters Clicker Where are we? Why was it s difficult t figure ut where in the Milky Way are the Sun and Earth lcated, and if urs is the nly nebula (galaxy)? A. We are immersed in a sup f stars, gas and dust, s hard t see far B. In a middle f city f stars, hard t figure shape f verall `metrplitan area C. Gas and dust can absrb light, making distance estimates uncertain D. All f the abve D. We might prefer t lk like this! Prettier? M101 with mre distinctive spiral arms 2

3 Cmpsite f M101 much ges n! Disk is very thin! (relatively speaking) Artist's sketch Pre-Milky Way: early hal + disk Galaxy NGC 4565 à nearly edge-n REAL IMAGE! What are galaxies made f? Hw t build a spiral galaxy (r s we think!) M104 Smbrer Galaxy 3

4 Inventry f stuff making up ur galaxy Stars Gas Ingredients f Interstellar Medium (ISM) (stuff between the stars) Very cld gas: star birth + dark matter Dust Cl gas: neutral H Ht H Mre stuff in ISM inventry Really ht gas States f gas in ISM Nw let us lk at them in turn. Dust Cld Stuff Dark Mlecular cluds (10 s f Kelvin) Gas & Dust Heated by stars t 100s-1000s Kelvin Absrbs visible and UV light Warm Stuff Hrsehead in clse-up Transparent t lnger wavelengths Infrared, radi Emits its wn infrared light Hrsehead Nebula 4

5 Ht Stuff Inizatin nebulae Trifid Nebula (M20) visible Spitzer infrared Ht (yung) stars inize hydrgen and ther elements in the gas T~ 10,000 K near ht yung stars Trifid Nebula Emissin nebulae O & B star assciatins Where the emissin clrs cme frm.. Emissin lines frm hydrgen and ther inized elements T~ 10,000 K near ht yung stars Lagn Bubbles f ht gas blwn ut by SUPERNOVAE T = millins f degrees K Mixing with rest f galactic gas à enrichment with heavy elements Really Ht Stuff REALLY HOT STUFF Synchrtrn emissin frm SNR X-ray and radi Traces very ht gas bubbles (SNR) Fast electrns & magnetic fields 29 Cass A SN remnant Flamsteed ~1680 Chandra X-ray image f Tych Brahe 1572 supernva remnant 5

6 Super-bubbles Super-bubbles in spiral galaxy NGC 3079 When multiple bubbles jin (frm a cluster) they can create superbubbles. If the superbubbles reaches the edge f the disk, it can blast ht gas ut f the Galaxy! Sme will rain back dwn and mix int the galaxy Artist's cnceptin/cmputer simulatins HST Super-bubbles in Large Magellanic Clud (LMC) (nearby galaxy) Clicker Pll f Advice Hw d yu take ntes (r listen) during lectures? A. I get mst f it by just listening B. I write dwn sme ntes, then g back t bk t lk things up C. I listen, take sme ntes, then get cpies f lecture slides frm curse website D. I enjy talking with my buddies, and they tell me later if I missed anything E. I try t read the subject in advance, and then listen, taking sme ntes in class All spiral galaxies are cnstantly changing Cycle f The starà Star-Gas- gas Star Cycle à star Reading ahead clicker mapping ur galaxy We want t map the structures f very cld gas within the dusty disk f the Milky Way. What wavelengths shuld we be using, and why? A. radi B. visible light C. x-rays A. 6

7 A. Radi Dust bscures ur visin f much f the galaxy in visible and UV light. X-rays nly highlight the httest and weirdest places 21 cm radi waves map nrmal hydrgen gas -- these pass thrugh dust unaffected cnfused visible image MW disk in radi ISM: A little DUST ges a lng way! Reddens the light Absrbs the light SEMI-WARM stuff: dust DUST: absrbs visible and UV light Transparent t lng wavelengths (red, IR, radi) Emits IR light Hrsehead Nebula 7