1ASTR 1040 ASTR 1040 AccelAccelAstroAstro::Stars & GalaxiesStars & GalaxiesProf. Prof. JuriJuriToomreToomreTA: Nicholas NelsonTA: Nicholas NelsonLecture 13 Tues 22 Feb 2011Lecture 13 Tues 22 Feb 2011zeus.colorado.edu/astr1040zeus.colorado.edu/astr1040--toomretoomreEtchedEtchedHourglassHourglassNebulaNebulaToday +Today +••Tour of the spring skyTour of the spring skyand star forming regions with and star forming regions with planetarium projector Fritzplanetarium projector Fritz••Discuss Discuss how a star may be bornhow a star may be born: : getting to the getting to the main sequence (MS)main sequence (MS)••Look at postLook at post--MS evolution of a MS evolution of a lowlow--mass starmass star••ConsiderConsiderred giantred giant(RG I)(RG I)phase, with H shell phase, with H shell burningburning••Helium flashHelium flashgoes off in shrinking degenerate core: goes off in shrinking degenerate core: horizontal branchhorizontal branchstar with He core burningstar with He core burning••Homework Set 5.5 due today, new HW #6 availableHomework Set 5.5 due today, new HW #6 available••Summary sheet on Summary sheet on stellar evolutionstellar evolutionavailableavailable••Term project on Term project on ExtraExtra--Solar PlanetsSolar Planetsusing using Planet Planet FinderFinderdistributed; help session Thurs 1distributed; help session Thurs 1--3pm3pmOur Milky Way GalaxyOur Milky Way Galaxy••200200--400400billionbillionstarsstars••100,000 light years 100,000 light years in in diameterdiameter, or, or~ 30,000 pc = ~ 30,000 pc = 30 30 kpckpc(kilo(kilo--parsecs)parsecs)••SunSunis located about is located about 8.5 8.5 kpckpcfrom center, from center, in the `Orion Armin the `Orion Arm’’ArtistArtist’’s sketch!s sketch!ooPERSPECTIVEPERSPECTIVEFOR STAR BIRTHFOR STAR BIRTHMilky Way Anatomy: Spiral GalaxyMilky Way Anatomy: Spiral Galaxy••DiskDisk::includes includes spiral armsspiral arms----young, new star young, new star formationformation••Bulge & HaloBulge & Halo::older stars, older stars, globular clustersglobular clustersDisk is very thin!Disk is very thin!ArtistArtist’’s edges edge--on viewon viewooIf If wewemight see might see Milky WayMilky Wayfrom outside from outside Spiral Spiral SbSbgalaxygalaxyNGC 4414NGC 4414oo2““Grand design spiralGrand design spiral””––M51 WhirlpoolM51 WhirlpoolBright Bright O & B O & B stars stars mark themark thespiral patternspiral pattern::regions ofregions ofstar birthstar birthDisk stars/gasDisk stars/gasrotate throughrotate through““traffic jamstraffic jams””The Star-Gas-Star CycleBIG disk recycling:BIG disk recycling:Cycle ofCycle ofstars stars gas gas stars stars Beauty and richness of the ISMBeauty and richness of the ISMEmission nebulae around Emission nebulae around star birth regionsstar birth regions----in dark clouds of obscuring dust and gasin dark clouds of obscuring dust and gasGravitational collapse of Gravitational collapse of ““molecular cloudsmolecular clouds””Battle between Battle between (1) (1) gravitygravitypulling inwardspulling inwardsbuilding building clumps, (2) clumps, (2) pressure ofpressure ofheated gasheated gaspushing outwardspushing outwardsto resist further collapseto resist further collapseNeed big clouds & cooling Need big clouds & cooling Simulation of Simulation of giant cloud giant cloud collapse and collapse and birth of starsbirth of starsWhat is the energyWhat is the energysourcesourcethat heats a that heats a contracting contracting protostarprotostar??A.A.FrictionFrictionB.B.Pressure, as the gas and dust are compressedPressure, as the gas and dust are compressedC.C.Gravitational potential energy released as the Gravitational potential energy released as the material is pulled inwardmaterial is pulled inwardD.D.FusionFusionE.E.Kinetic energyKinetic energyC.C.3Stages in building the PROTOSTARStages in building the PROTOSTARToo much angular momentum Too much angular momentum ––jet it away !jet it away !Actual edgeActual edge--on disk and jet (Hubble ST)on disk and jet (Hubble ST)Many jets from young stellar objectsMany jets from young stellar objectsOften Often protostarprotostaris still hidden in is still hidden in cocoon of dustcocoon of dust––and jets are and jets are episodicepisodic((HerbigHerbig--HaroHaroobjects)objects)More massiveMore massiveprotostarsprotostarsgetgetto MS faster !to MS faster !Reading clicker Reading clicker ––StarbirthStarbirth••The vast majority of stars in a newly formed The vast majority of stars in a newly formed star cluster are ________ ?star cluster are ________ ?••A.A.less massive than the Sun••B.B.very high-mass, type O and B stars••C.C.red giants••D.D.about the same mass as SunA.A.Collapse of molecular cloud makes many Collapse of molecular cloud makes many small stars, fewer massive O & B starssmall stars, fewer massive O & B stars4NGC 604NGC 604in M33in M33TriangulumTriangulumStar BirthStar BirthCauldronCauldronWhat happens to nuclear fusion when What happens to nuclear fusion when the hydrogen in a starthe hydrogen in a star’’s core runs low?s core runs low?••A.A.It stopsIt stops••B.B.It shifts from the core to a shell around It shifts from the core to a shell around the corethe core••C.C.Other elements start to fuseOther elements start to fuse••D.D.The star goes out of balance and The star goes out of balance and becomes a red giantbecomes a red giant••E.E.B and DB and DE.E.MS MS Red Giant I Red Giant I HorizHorizBranch Branch Red Giant IIRed Giant II(or Supergiant)(or Supergiant)MSMSRG IRG IRG IIRG IIOverview ofOverview ofwhat will happen:what will happen:1:1:LowLow--MassMassStar on MSStar on MSH burning in H burning in corecoreLongest phaseLongest phase::10,000 MY = 10 BY10,000 MY = 10 BYif solar massif solar mass2:2:SubgiantSubgianttotoRed GiantRed Giant(first visit)(first visit)H burning in H burning in shell,shell,makes much moremakes much moreenergyenergyVast expansion,Vast expansion,RG phase lastsRG phase lasts~ 500 MY~ 500 MYHuge convectiveHuge convectiveenvelopeenvelopeMS MS subgiantsubgiantred giantred giant5MS MS subgiantsubgiantred giantred giantContracting core in red giant gradually becomes Contracting core in red giant gradually becomes ““electron degenerateelectron degenerate””----what does that mean?what does that mean?MSMSred giantred