TheFutureoftheSun(Note:notintextbook)

TheSunfuseshydrogenintoheliuminastablereaction.ButwhathappenswhentheSunrunsoutofhydrogeninitscore?

Thetimescaleforthisisabout10billionyears;weareabouthalfwaythere.

WhentheSunrunsoutofenergy,itsstructurehas tochange:stellarevolution.

TheFutureoftheSun(Note:notintextbook)

• NuclearfusionofHydrogenè HeliumprovidestheenergythathelpssupporttheSunagainstgravitationalcontraction.Withoutthat,theinnerregionswillcontractandheatup.

• Whenthathappens,thehydrogenjustoutsidethecorewillgethotenoughtostartfusingintoheliumevenmorequicklythanthecoredid:excessenergy.

• TheSunbrightensandtheouterregionsexpandandcool.TheSunbecomesaredgiant.

TheFutureoftheSun(Note:notintextbook)

EventuallythetemperatureofthecontractingHeliumcoregetssohighthatHeliumcanstartfusingintoCarbonandOxygenandreleaseenergy.TheSunsettlesdownforashorttime,muchbrighterthanbeforebutrelativelystable.

TheFutureoftheSun(Note:notintextbook)

• Only~100millionyearsafterstartingtoburnHelium,theSunwilluseupalltheHeliuminitscoreandhaveturneditintoCarbonandOxygen.Whatthen?

• SamethingthathappenedtomaketheSunaredgiant,exceptwithHeliumburninginashellaroundtheCarbon/Oxygencore.TheSunswellsevenmoreandbecomesaredsupergiant.

• Atthispoint,theSunisunstable,andtheenergyreleasedcomesinburstswhichcanactuallypushawaytheSun’s.outerlayers.

TheFutureoftheSun(Note:notintextbook)

• TheouterlayersoftheSunwillbepushedoutintospace,leavingbehindthesmallCarbon/Oxygencore.

• Theheatfromthiscorecausestheexpandingouterlayerstoshine,makingaplanetarynebula.

• Planetarynebulahavenothingtodowithplanets!

TheFutureoftheSun(Note:notintextbook)

• Aftertheouterlayersdriftawayandstopshining,allthatisleftbehindisthecoolingcoreofcarbonandoxygen,calledawhitedwarf.

• Itshinesfaintlybecauseitishot,butitsnothotenoughtodrivenuclearreactionsinvolvingcarbonoroxygen.

• Itisextremelydense,withamass abouthalfthatoftheSunandasizenotmuchlargerthantheEarth.

• Overbillionsofyears,thewhitedwarfsimplycoolsoffandfadesout.