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CU-Boulder ASTR 1120 - Lecture Notes

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ASTR 1120ASTR 1120General Astronomy:General Astronomy:Stars & GalaxiesStars & Galaxies!omework #6 - due Tue, Nov. 3.- " ext OBSERVIN# $ession:%ed, Oct. 28 &i.e. 'morrow(, 7p)Galaxies: Ultimate Galaxies: Ultimate Recyling Recyling PlantsPlantsREVIEWMolecular clouds =Molecular clouds =star forming regionsstar forming regionsCOLD STUFF•Molecular CLOUDS•Mostly atomic hydrogen, •some helium and •other molecules•Dark, dusty, cold10-30K•Emit molecular •emission lines •in far IR, radioSemi-Warm stuffSemi-Warm stuff••Dust:Dust:––absorbsabsorbs visible visibleand UV lightand UV light––TransparentTransparent to tolonglongwavelengthswavelengths(red, IR, radio)(red, IR, radio)••Emits IR lightEmits IR lightHorsehead Horsehead NebulaNebula••Hot stars ionizeHot stars ionizehydrogen and otherhydrogen and otherelements in the gaselements in the gas••T~ 10,000 K nearT~ 10,000 K nearhot young starshot young starsIonization nebulaeIonization nebulae““O & B star O & B star associationsassociations””Lagoon NebulaLagoon NebulaHot stuffHot stuff(10 (10 ly ly across)across)Really Hot StuffReally Hot StuffHot starHot starwinds fromwinds fromaging starsaging starsSupernovaSupernovaRemnantsRemnants&&PlanetaryPlanetaryNebulaNebulaMore hot stuffMore hot stuffSome stuff is Some stuff is REALLY HOTREALLY HOT••Bubbles of hot gasBubbles of hot gasblown out byblown out bySUPERNOVAESUPERNOVAE••T = tens of millionsT = tens of millionsof degrees Kof degrees K••Mixing with rest ofMixing with rest ofgalactic gas galactic gas !!enrichment withenrichment withheavy elementsheavy elementsSuperbubbles Superbubbles & Fountains& Fountains••WhenWhen multiple bubblesmultiple bubblesjoin (from a cluster) theyjoin (from a cluster) theycan create can create superbubblessuperbubbles..••Superbubbles Superbubbles cancan blastblasthot gashot gas eveneven out of theout of theGalaxy!Galaxy!••““EnrichesEnriches”” gas between gas betweengalaxiesgalaxies••Some will rain back downSome will rain back downand mix into the Galaxyand mix into the GalaxyArtistsArtists’’ conceptions! conceptions!Inside our Galaxy: Material isInside our Galaxy: Material isConstantly Being RecycledConstantly Being RecycledSummary of Galactic RecyclingSummary of Galactic Recycling• Stars make new elements by fusion• Dying stars expel gas and new elements, producinghot bubbles (~106 K)• Hot gas cools, allowing atomic hydrogen clouds toform (~100-10,000 K)• Further cooling permits molecules to form, makingmolecular clouds (~30 K)• Gravity forms new stars (and planets) in molecularcloudsGas CoolsFrom HOTHOT to COLDCOLDIs the process of galactic recyclingIs the process of galactic recyclinggoing to continue to infinity?going to continue to infinity?A. YesB. NOClicker QuestionClicker QuestionBE PREPARED TODEFEND YOUR ANSWERIs the process of galactic recyclingIs the process of galactic recyclinggoing to continue to infinity?going to continue to infinity?A. YesB. NOClicker QuestionClicker QuestionBE PREPARED TODEFEND YOUR ANSWERThe ages of stars suggest that the bulgeThe ages of stars suggest that the bulgeand halo of the Milky Way formed beforeand halo of the Milky Way formed beforemany of the stars in the disk. Which wouldmany of the stars in the disk. Which wouldyou expect to have you expect to have more heavy metalsmore heavy metals(a.k.a. higher (a.k.a. higher metallicitymetallicity)?)?A.A.Halo and bulge starsHalo and bulge starsB.B.Disk starsDisk starsC.C.No differenceNo differenceClicker QuestionClicker QuestionThe ages of stars suggest that the bulgeThe ages of stars suggest that the bulgeand halo of the Milky Way formed beforeand halo of the Milky Way formed beforemany of the stars in the disk. Which wouldmany of the stars in the disk. Which wouldyou expect to have you expect to have more heavy metalsmore heavy metals(a.k.a. higher (a.k.a. higher metallicitymetallicity)?)?A.A.Halo and bulge starsHalo and bulge starsB.B.Disk starsDisk starsC.C.No differenceNo differenceClicker QuestionClicker QuestionWe observe star-gas-star cycle operating in Milky WayWe observe star-gas-star cycle operating in Milky Way’’ssdisk using many different wavelengths of lightdisk using many different wavelengths of lightInfrared light reveals stars whose visible light isInfrared light reveals stars whose visible light isblocked by gas cloudsblocked by gas cloudsInfraredVisibleX-rays are observed from hot gas above and below theX-rays are observed from hot gas above and below theMilky WayMilky Way’’s disks diskX-raysWe also see “point” sources – these are X-ray binaries21 cm radio waves emitted by atomic hydrogen show21 cm radio waves emitted by atomic hydrogen showwhere gas has cooled and settled into diskwhere gas has cooled and settled into diskRadio (21cm)Radio waves from carbon monoxide (CO) showRadio waves from carbon monoxide (CO) showlocations of molecular cloudslocations of molecular cloudsRadio (CO)Long-wavelength infrared emission shows whereLong-wavelength infrared emission shows whereyoung stars are heating dust grainsyoung stars are heating dust grains IR(dust)Gamma rays show where cosmic rays from supernovaeGamma rays show where cosmic rays from supernovaecollide with atomic nuclei in gas cloudscollide with atomic nuclei in gas clouds ! -RaysOutlining Outlining starbirth starbirth in M51in M51VisibleVisible((Kitt Kitt Peak)Peak)InfraredInfrared(Spitzer)(Spitzer)What Clues to Our GalaxyWhat Clues to Our Galaxy’’ssHistory Do Halo & Disk StarsHistory Do Halo & Disk StarsHold?Hold?Halo Stars: 0.02-0.2% heavy elements (O, Fe, …).Disk Stars: 2% heavy elementsWhich stars formed first?Which stars formed first?A. Halo starsB. Disk starsC. All stars formed at the same timeD. Not enough information given Clicker QuestionClicker QuestionWhich stars formed first?Which stars formed first?A. Halo starsB. Disk starsC. All stars formed at the same timeD. Not enough information given Clicker QuestionClicker QuestionDisk Stars: 2% heavy elements, stars of all ages, large fraction of young stars (Population IPopulation I)Halo Stars: 0.02-0.2% heavy elements (O, Fe, …), only old stars. (called Population IIPopulation II)Halo starsformed first,then stoppedWhat kind of star is most likely to be aWhat kind of star is most likely to be apart of thepart of the Halo population?Halo population?A. An O starB. An A starC. An M starD. All stars are equally


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CU-Boulder ASTR 1120 - Lecture Notes

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