Class Notes (1,000,000)
CA (620,000)
WLU (20,000)
AS (200)
AS101 (200)
Lecture 8

AS101 Lecture Notes - Lecture 8: Supergiant, Giant Star, Triple-Alpha ProcessPremium


Department
Astronomy
Course Code
AS101
Professor
Ioannis John Haranas
Lecture
8

This preview shows half of the first page. to view the full 3 pages of the document.
AS101Lecture8TheDeathsofStars

GiantStars
Giantstar:Large,cool,highlyluminousstarintheupperrightcorneroftheHRdiagram,
typically10to100timesthediameteroftheSun.
Supergiantstar:Exceptionallyluminousstarwhosediameteris100to1000timesthatofthe
Sun.
Starsenterthegiantstageafterexhaustingalltheirhydrogeninthemainsequencestage.
Astarcanonlyremaininthegiantstageforabout10percentofitstotallifetime
Nova:Asuddenandtemporarybrighteningofastarmakingitappearasanewstarinthesky,
evidentlycausedbyanexplosionofnuclearfuelonthesurfaceofawhitedwarf.
Supernova:Anewstarintheskythatisroughly4000timesmoreluminousthananormalnova
andlongerlasting,theresultofanexplosionofastar

Expansionintoagiantstar
Heliumhasaccumulatedinamainsequencestar’score,reducingitsabilitytogeneratenuclear
energy
Coreofstargrowshotterandtriggersfusionofhydrogenintheoutershell
Whenthecorereachesatemperatureof100000000K,theheliumcanbeginfusinginto
carbon

Heliumfusion
Changesthestructureofthestar
oHeliumfusioninthecore
oHydrogenfusioninthesurroundingshell
Horizontalbranch:thelocationintheHRdiagramofgiantstarsfusinghelium
Producescarbonandoxygenthataccumulateinaninertcore

TheDeathsoflowmassstars
Verylowmassstarsarereddwarfs,(>0.4solarmass),haveverylonglivesbecausetheyhave
completelyconvectiveandconsumetheirhydrogenveryslowly
oCanlive100billionyearsormore

Mediummassstars(0.44solarmass):thereisalackofcompletemixingandmasslossduring
theredgiantstage
Thesestarsproduceplanetarynebulae(anexpandingshellofgasejectedfromamediummass
starduringthelatterstagesofitsevolution),andthenturnintowhitedwarfs

WhiteDwarfs
Hot,small,veryhighdensities
Secondmostcommonkindofstar
Degeneratematter:Extremelyhighdensitymatterinwhichpressurenolongerdependson
temperatureduetoquantummechanicaleffects
You're Reading a Preview

Unlock to view full version

Subscribers Only