ASTR 1120 ASTR 1120 General Astronomy: General Astronomy: Stars & Galaxies Stars & Galaxies � omework #6 - due Tue, Nov. 3. - � ex ext O OBSERVIN IN � � es ession ion: � ed ed, O , Oct. 2 . 28 � i.e. i.e. � morrow orrow � , 7 , 7p �
REVIEW Galaxies: Ultimate Recyling Recyling Plants Plants Galaxies: Ultimate
Molecular clouds = Molecular clouds = COLD STUFF star forming regions star forming regions •Molecular CLOUDS •Mostly atomic hydrogen, •some helium and •other molecules •Dark, dusty, cold 10-30K •Emit molecular •emission lines •in far IR, radio
Semi-Warm stuff Semi-Warm stuff • Dust: Dust: • – absorbs absorbs visible visible – and UV light and UV light – Transparent Transparent to to – long long wavelengths wavelengths (red, IR, radio) (red, IR, radio) • Emits IR light Emits IR light • Horsehead Nebula Nebula Horsehead
Hot stuff Hot stuff Ionization nebulae Ionization nebulae “O & B star O & B star “ associations” ” associations • Hot stars ionize Hot stars ionize • hydrogen and other hydrogen and other elements in the gas elements in the gas • T~ 10,000 K near T~ 10,000 K near • hot young stars hot young stars Lagoon Nebula Lagoon Nebula
Really Hot Stuff Really Hot Stuff Hot star Hot star winds from winds from aging stars aging stars (10 ly ly across) across) (10
More hot stuff More hot stuff Planetary Supernova Planetary Supernova & & Nebula Remnants Nebula Remnants
Some stuff is REALLY HOT REALLY HOT Some stuff is • Bubbles of hot gas Bubbles of hot gas • blown out by blown out by SUPERNOVAE SUPERNOVAE • T = tens of millions • T = tens of millions of degrees K of degrees K • Mixing with rest of Mixing with rest of • galactic gas � � galactic gas enrichment with enrichment with heavy elements heavy elements
Superbubbles & Fountains & Fountains Superbubbles • When multiple bubbles multiple bubbles • When join (from a cluster) they join (from a cluster) they can create superbubbles superbubbles. . can create • Superbubbles can can blast blast • Superbubbles hot gas even even out of the out of the hot gas Galaxy! Galaxy! • “Enriches Enriches” ” gas between gas between • “ galaxies galaxies • Some will rain back down • Some will rain back down and mix into the Galaxy and mix into the Galaxy Artists’ ’ conceptions! conceptions! Artists
Inside our Galaxy: Material is Inside our Galaxy: Material is Constantly Being Recycled Constantly Being Recycled
Summary of Galactic Recycling Summary of Galactic Recycling From HOT HOT to COLD COLD • Stars make new elements by fusion • Dying stars expel gas and new elements, producing Gas Cools hot bubbles (~10 6 K) • Hot gas cools, allowing atomic hydrogen clouds to form (~100-10,000 K) • Further cooling permits molecules to form, making molecular clouds (~30 K) • Gravity forms new stars (and planets) in molecular clouds
Clicker Question Clicker Question Is the process of galactic recycling Is the process of galactic recycling going to continue to infinity? going to continue to infinity? A. Yes B. NO BE PREPARED TO DEFEND YOUR ANSWER
Clicker Question Clicker Question Is the process of galactic recycling Is the process of galactic recycling going to continue to infinity? going to continue to infinity? A. Yes B. NO BE PREPARED TO DEFEND YOUR ANSWER
Clicker Question Clicker Question The ages of stars suggest that the bulge The ages of stars suggest that the bulge and halo of the Milky Way formed before and halo of the Milky Way formed before many of the stars in the disk. Which would many of the stars in the disk. Which would you expect to have more heavy metals more heavy metals you expect to have (a.k.a. higher metallicity metallicity)? )? (a.k.a. higher A. Halo and bulge stars Halo and bulge stars A. B. Disk stars Disk stars B. C. No difference No difference C.
Clicker Question Clicker Question The ages of stars suggest that the bulge The ages of stars suggest that the bulge and halo of the Milky Way formed before and halo of the Milky Way formed before many of the stars in the disk. Which would many of the stars in the disk. Which would you expect to have more heavy metals more heavy metals you expect to have (a.k.a. higher metallicity metallicity)? )? (a.k.a. higher A. Halo and bulge stars Halo and bulge stars A. B. Disk stars Disk stars B. C. No difference No difference C.
We observe star-gas-star cycle operating in Milky Way’ ’s s We observe star-gas-star cycle operating in Milky Way disk using many different wavelengths of light disk using many different wavelengths of light
Infrared light reveals stars whose visible light is Infrared light reveals stars whose visible light is blocked by gas clouds blocked by gas clouds Infrared Visible
X-rays are observed from hot gas above and below the X-rays are observed from hot gas above and below the Milky Way’ ’s disk s disk Milky Way X-rays We also see “point” sources – these are X-ray binaries
21 cm radio waves emitted by atomic hydrogen show 21 cm radio waves emitted by atomic hydrogen show where gas has cooled and settled into disk where gas has cooled and settled into disk Radio (21cm)
Radio waves from carbon monoxide (CO) show Radio waves from carbon monoxide (CO) show locations of molecular clouds locations of molecular clouds Radio (CO)
Long-wavelength infrared emission shows where Long-wavelength infrared emission shows where young stars are heating dust grains young stars are heating dust grains IR (dust)
Gamma rays show where cosmic rays from supernovae Gamma rays show where cosmic rays from supernovae collide with atomic nuclei in gas clouds collide with atomic nuclei in gas clouds � -Rays
Outlining starbirth starbirth in M51 in M51 Outlining Visible Infrared Visible Infrared (Kitt Kitt Peak) Peak) (Spitzer) ( (Spitzer)
What Clues to Our Galaxy’ ’s s What Clues to Our Galaxy History Do Halo & Disk Stars History Do Halo & Disk Stars Hold? Hold?
Halo Stars: 0.02-0.2% heavy elements (O, Fe, …). Disk Stars: 2% heavy elements
Clicker Question Clicker Question Which stars formed first? Which stars formed first? A. Halo stars B. Disk stars C. All stars formed at the same time D. Not enough information given
Clicker Question Clicker Question Which stars formed first? Which stars formed first? A. Halo stars B. Disk stars C. All stars formed at the same time D. Not enough information given
Halo Stars: Halo stars 0.02-0.2% heavy elements (O, Fe, …), formed first, only old stars. (called Population II Population II ) then stopped Disk Stars: 2% heavy elements, stars of all ages, large fraction of young stars ( Population I Population I )
Clicker Question Clicker Question What kind of star is most likely to be a What kind of star is most likely to be a part of the Halo population? Halo population? part of the A. An O star B. An A star C. An M star D. All stars are equally likely E. There are no stars left in the spheroidal population. Only supernova remnants.
Clicker Question Clicker Question What kind of star is most likely to be a What kind of star is most likely to be a part of the Halo population? Halo population? part of the A. An O star B. An A star C. An M star D. All stars are equally likely E. There are no stars left in the spheroidal population. Only supernova remnants.
Halo Stars: Halo stars 0.02-0.2% heavy elements (O, Fe, …), formed first, only old stars. (called Population II Population II ) then stopped Disk Stars: Disk stars 2% heavy elements, formed later, stars of all ages ( Population I Population I ) kept forming
How Did Our Galaxy Form? How Did Our Galaxy Form?
Our galaxy probably formed from a giant gas cloud Our galaxy probably formed from a giant gas cloud
Halo stars formed first as gravity caused cloud to contract Halo stars formed first as gravity caused cloud to contract
Remaining gas settled into spinning disk Remaining gas settled into spinning disk
Stars continuously form in disk as galaxy grows older - Stars continuously form in disk as galaxy grows older - stars remain in disk plane stars remain in disk plane
Warning: This model is oversimplified Careful study of heavy-element proportions suggests that our galaxy formed from a few different clouds.
Detailed studies: Halo stars formed in clumps that later Detailed studies: Halo stars formed in clumps that later merged merged
Galactic Creation Summary Galactic Creation Summary • What clues to our galaxy What clues to our galaxy’ ’s history do s history do • halo stars hold? halo stars hold? – Halo stars are all old, with a smaller proportion of heavy elements than disk stars, indicating that the halo formed first • How did our galaxy form? How did our galaxy form? • – Our galaxy formed from a few huge clouds of gas, with the halo stars forming first and the disk stars forming later, after the gas settled into a spinning disk
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