ASTR 1120ASTR 1120General Astronomy:General Astronomy:Stars & GalaxiesStars & Galaxies•• Homework #4Homework #4 on Mastering Astronomy, on Mastering Astronomy, due on Thursday of next week, 10/08, by 5pmdue on Thursday of next week, 10/08, by 5pm• Next Extra Credit Observing Night:–Thursday, 10/08 at Sommers-BauschLast class:Last class: When a Low-Mass Star When a Low-Mass Starruns out of Hydrogen in its Coreruns out of Hydrogen in its Core1. With fusion no longeroccurring in the core,gravity causes coregravity causes corecollapsecollapse2. Hydrogen shell startsfusion, lifting outer layers.Red GiantRed Giant increasesluminosity.3. Under degenerateconditions, core becomeshot enough to fuseHelium: Helium FlashHelium Flash4. Outer layers fall and heat,luminosity decreases.Helium burns stably:Horizontal Branch StarHorizontal Branch StarA star moves upwards and to theA star moves upwards and to theright on the HR diagram. What isright on the HR diagram. What isprobably happening probably happening in the corein the core??A. The core has just started to burn a new elementB. All nuclear burning is slowing downC. The inner core temperature is coolingD. The inner core is collapsing and heating up;shell burning is increasingClicker QuestionClicker QuestionA star moves upwards and to theA star moves upwards and to theright on the HR diagram. What isright on the HR diagram. What isprobably happening probably happening in the corein the core??A. The core has just started to burn a new elementB. All nuclear burning is slowing downC. The inner core temperature is coolingD. The inner core is collapsing and heating up;shell burning is increasingClicker QuestionClicker QuestionHR Diagram for an old globular clusterHR Diagram for an old globular clusterHelium FusionHelium Fusion• Temperatures ~ 100million K• He + He + He ! C +energy– Triple-alpha processWhat Will Happen When ThereWhat Will Happen When ThereIs No More Helium in the Core?Is No More Helium in the Core?A. The core will cool down.B. Carbon fusion will start immediately.C. The star will explode.D. The core will start to collapse.E. The hydrogen fusing shells will go out.Clicker QuestionClicker QuestionWhat Will Happen When ThereWhat Will Happen When ThereIs No More Helium in the Core?Is No More Helium in the Core?A. The core will cool down.B. Carbon fusion will start immediately.C. The star will explode.D. The core will start to collapse.E. The hydrogen fusing shells will go out.Clicker QuestionClicker QuestionWhen helium runs outWhen helium runs out……..• Carbon core collapsescollapses and heats upheats up• Burning in helium AND hydrogen shells– Shell burning now unstable = Thermal PulsesThermal Pulses• Energy generationbecomes much higheragainagain• Outer layers lift andcool againagain• Star becomes veryluminous red giantred giant– Class II• Degeneracy pressurereached before T=600million K– No carbon fusion• Stellar winds blowmaterial from the outside––including some carbonincluding some carbon• Outer layers thrown off ina big puffbig puff around theinert carbon coreinert carbon core––Big puff =Big puff = Planetary NebulaPlanetary Nebula––Inert carbon coreInert carbon core = = WhiteWhiteDwarfDwarf• Slowly cools and fadesuntil it becomes a nearlyinvisible “black dwarf”Spirograph Spirograph nebulanebulaIC 418: The Spirograph nebulaNGC 6826NGC 6826NGC 6826: The Blinking Eye NebulaEskimo NebulaEskimo NebulaNGC 2392: The Eskimo NebulaHelix NebulaHelix NebulaNGC 7293: The Helix NebulaMore Planetary NebulaeMore Planetary Nebulae!HAS IS A WHITE DWARF?!HAS IS A WHITE DWARF? Exposed core of a low-mass star that has diedNo fusion to maintain heat and pressure to balance gravity pullElectron degeneracy pressureElectron degeneracy pressure balancesinward crush of its own gravityMostly made of Carbon and Oxygen Very high density and hence gravityMaximum mass=1.4 Msun (Chandrasekar limit)Size Of A White DwarfSize Of A White DwarfSize ofEarthFunky properties of white dwarf material1 Kg chocolate cake2 Kg chocolate cake0.4 Msun white dwarf0.8 Msun white dwarf• Hubble SpaceTelescope spies12-13 billion year12-13 billion yearoldold white dwarfs– Formed less than1 billion yearsafter the creationof the universe© HST and H. Richer(University of BritishColumbia)Which is correct order for someWhich is correct order for somestages of lifestages of life in a low-mass star? in a low-mass star?A.A.protostarprotostar, main-sequence star, red giant,, main-sequence star, red giant,planetary nebula, white dwarfplanetary nebula, white dwarfB.B.protostarprotostar, main-sequence star, red giant,, main-sequence star, red giant,supernova, neutron starsupernova, neutron starC.C.main-sequence star, white dwarf, red giant,main-sequence star, white dwarf, red giant,planetary nebula, planetary nebula, protostarprotostarD.D.protostarprotostar, main-sequence star, planetary, main-sequence star, planetarynebula, red giantnebula, red giantE.E.protostarprotostar, red giant, main-sequence star,, red giant, main-sequence star,planetary nebula, white dwarfplanetary nebula, white dwarfClicker QuestionClicker QuestionWhich is correct order for someWhich is correct order for somestages of lifestages of life in a low-mass star? in a low-mass star?A.A.protostarprotostar, main-sequence star, red giant,, main-sequence star, red giant,planetary nebula, white dwarfplanetary nebula, white dwarfB.B.protostarprotostar, main-sequence star, red giant,, main-sequence star, red giant,supernova, neutron starsupernova, neutron starC.C.main-sequence star, white dwarf, red giant,main-sequence star, white dwarf, red giant,planetary nebula, planetary nebula, protostarprotostarD.D.protostarprotostar, main-sequence star, planetary, main-sequence star, planetarynebula, red giantnebula, red giantE.E.protostarprotostar, red giant, main-sequence star,, red giant, main-sequence star,planetary nebula, white dwarfplanetary nebula, white dwarfClicker QuestionClicker QuestionTime scales for EvolutionTime scales for Evolutionof Sun-like Starof Sun-like StarH core burningMain SequenceMain Sequence10101010 yr yr10 billion years10 billion yearsInactive He core, H shell burning Red GiantRed Giant101088 yr yr100 million years100 million yearsHe core burning (unstable), ”Helium FlashHelium FlashHoursHoursHe core burning (stable), ”Horizontal BranchHorizontal Branch101077 yr yr10 million years10 million yearsC core, He + H shells burningBright Red