evoluon of high mass stars - texas a&m...

Evolu&onofHighMassStars

Astronomy101

HighMassStars

•  O&BStars(M>4Msun):– BurnHot– LiveFast– DieYoung

•  MainSequencePhase:– BurnHtoHeincoreviaCNOcycle– BuildupaHecore,likelow‐massstars– Lastsforonly~10Myr

MaximumMass:60-100Msun

•  Ifastaristoomassive,thecoregetssohotthat:– Radia&onpressureovercomesgravity– Starbecomesunstable&disrupts.

•  Ul&matelimitisnotpreciselyknown

•  Suchstarsshouldbeveryrare.•  Massivestarsliveontheedge...

RedSupergiantPhase

•  AYerHcoreexhaus&on:–  InertHecorecontracts&heatsup– HburninginashellaroundtheHecore– Huge,puffyenvelope~sizeoforbitofJupiter

•  MoveshorizontallyacrosstheH‐Rdiagram:– Takes~1MyrtocrossH‐Rdiagram

CrossingtheSupergiantBranch

40,000 20,000 10,000 5,000 2,500

106

104

102

1

10 -2

10 -4

Temperature (K)

Lum

inos

ity (L

sun)

Red Supergiant

RedSupergiantStar

Inert He

Core

H Burning Shell

Cool, Extended Envelope

Not to Scale

HeliumFlash

•  CoreTemperaturereaches170MillionK•  IgnitesHeliumburningtoC&O:– RapidPhase:~1Myr

– Heburninginthecore– Hburninginashell– StartbuildingaC‐Ocore

•  StarbecomesaBlueSupergiant.

BlueSupergiant

40,000 20,000 10,000 5,000 2,500

106

104

102

1

10 -2

10 -4

Temperature (K)

Lum

inos

ity (L

sun)

Blue Supergiant

Helium Flash

HeCoreExhaus&on

•  WhenHerunsoutinthecore:–  InertC‐Ocorecollapses&heatsup– H&Heburningmovesintoshells– BecomesaRedSupergiantagain

•  C‐OCorecollapsesun&l:– Tcore>600MillionK– density>150,000g/cc

•  IgnitesCarbonBurningintheCore.

EndofHeliumBurning

40,000 20,000 10,000 5,000 2,500

106

104

102

1

10 -2

10 -4

Temperature (K)

Lum

inos

ity (L

sun)

CarbonBurning:

•  Nuclearreac1onnetwork:12C+12Cfusesto:–  24Mg–  20Ne+4He–  16O+2×4He

•  BuildupaninertO‐Ne‐Mgcore

•  Veryinefficient:– Makesmanyneutrinos– Lastsonly~1000yearsbeforeCrunsout.

EndofCarbonBurningPhase:

Inert O-Ne-Mg

Core

C Burning Shell

Red Supergiant Envelope

He Burning Shell

H Burning Shell

IntermediateMassStars

•  Starswith4<M<8Msun•  AYer1000years:–  InertO‐Ne‐Mgcorecontracts&heatsup

– C,He,&Hburningshells•  Thermalpulsesdestabilizetheenvelope:– Ejecttheenvelopeinamassivestellarwind.

– LeaveO‐Ne‐Mgwhitedwarfcorebehind.

HighMassStars:M>8Msun

•  AttheonsetofCarbonBurning:– Evolu&onissofastthattheenvelopecannolongerrespond.

– Shouldseelijleoutwardsignoftheinwardturmoiltocome.

•  Excep&on:Strongstellarwindscanerodetheenvelope,changingtheoutwardappearanceofthestar.

NeonBurning

•  O‐Ne‐Mgcorecontracts&heatsupun&l:– Tcore~1.5BillionK– density~107g/cc

•  IgniteNeonburning:–  reac&onnetworkmakesO,Mg,&others– Hugeneutrinolosses:>L*!– BuildsaheavyO‐Mgcore

•  LastsforafewyearsbeforeNerunsout.

OxygenBurning

•  Nerunsout,corecontracts&heatsupun&l:– Tcore~2.1BillionK– density~fewx107g/cc

•  IgniteOxygenburning:–  reac&onnetworkmakingSi,S,P,&others– Hugeneutrinolosses:>100,000L*!– BuildsaheavySicore.

•  Lastsfor~1yearbeforeOrunsout.

SiliconBurning

•  Orunsout,Sicorecontracts&heatsupun&l:– Tcore~3.5BillionK– density~108g/cc

•  IgniteSiliconburning:– Simeltsintoaseaof4He,p,&n– FuseswithrestintoNickel(Ni)&Iron(Fe)– BuildsaheavyNi/Fecore.

•  Lastsfor~1day...

TheNuclearImpasse

•  Fusionoflightelementsreleasesnuclearbindingenergy.

•  Iron(Fe)isthemost&ghtlyboundnucleus:– FusionofnucleilighterthanFereleaseenergy.– FusionofnucleiheavierthanFeabsorbenergy.

•  OnceanFecoreforms,therearenonewfusionreac&onsleYforthestartotap.

EndofSiliconBurningPhase:

Inert Fe-Ni Core

Si Burning Shell

O Burning Shell

Ne Burning Shell

C Burning Shell

He Burning Shell

H Burning Shell

Envelope: ~ 5 AU

Core Radius: ~1 Rearth

EndoftheRoad

•  AttheendoftheSiliconBurningDay:– StarbuildsupaninertFecore– Seriesofnestednuclearburningshells

•  Finally,theFecoreexceeds1.2-2Msun:– Fecorebeginstocontract&heatup.– Thiscollapseisfinal&catastrophic

LastDaysofaMassiveStar

•  Burnasuccessionofnuclearfuels:– Hydrogenburning:10Myr– Heliumburning:1Myr– Carbonburning:1000years– Neonburning:~10years– Oxygenburning:~1year– Siliconburning:~1day

•  BuildupaninertIroncoreinthecenter.

InsideaMassiveStarontheBrink:

Inert Fe-Ni Core

Si Burning Shell

O Burning Shell

Ne Burning Shell

He Burning Shell

C Burning Shell

H Burning Shell

Envelope: ~ 5 AU

Core Radius: ~1 Rearth

IronCoreCollapse

•  IroncorewithM~1.2‐2Msun– Collapses&beginstoheatup– ReachesT>10BillionK&density~1010g/cc

•  Twoenergyconsumingprocesseskickin:1)NucleiphotodisintegrateintoHe,p&n

2)protons&electronscombinetoformneutrons&neutrinos.Neutrinosescape.

•  Bothrobenergy,hasteningthecore’scollapse

CatastrophicCollapse

•  StartofIronCorecollapse:– Radius~6000km(~Rearth)

– Density~108g/cc•  Within1second:– Radius~50km– Density~1014g/cc– CollapseSpeed~0.25c!

CoreBounce

•  Densityofcollapsingcorehits~2.4x1014g/cc=densityofatomicnuclei!

•  Strongnuclearforcecomesintoplay!

•  Inner0.7Msunofthecore:– comestoascreechinghalt– overshoots&springsbackalijle(“bounces”)

•  Infallinggashitsthebouncingcorehead‐on!

Post‐BounceShockwave

•  Shockwavespreadsoutfromcorebounce:– Kine&cEnergyis~1051ergs!– StallsoutaYeronly25‐40millisecbecauseofatrafficjambetweeninfalling&ouplowinggas.

•  Meanwhile,neutrinospouroutofthecore:–  trappedbythedensesurroundinggas–  leadstorapidhea&ngofthegas–  inturnleadstoviolentconvec&on

New,ImprovedShockwave

•  Violentconvec&onbreaksthetrafficjam

•  Shockwaveisregeneratedin~300millisec.

•  Smashesoutthroughthestar:–  Breakoutspeed~0.1c!–  Explosivenuclearfusioninwakeofblastproducesmoreheavyelements

– Heatsupandacceleratesenvelopegas•  Inafewhours,shockbreaksoutofthesurface

Supernova!

•  Atshockbreakout:– Starbrightensto~10BillionLsuninminutes.

– Canoutshineanen&regalaxyofstars!•  Outerenvelopeblastedoff:– acceleratedtoafew×10,000km/sec– gasexpands&coolsoff

•  Supernovafadesoutoverafewmonths.

HistoricalSupernovae

•  1054AD:“GuestStar”inTaurusobservedbyChineseastronomers(Songdynasty).– Visibleindaylightfor23days.

•  1572:TychoBrahe’sSupernova•  1604:JohannesKepler’sSupernova•  6000‐8000BC:Velasupernova– observedbytheSumerians;appearsinlegendsaboutthegodEa.

CrabSupernova

Supernova1987a

•  Nearestvisiblesupernovasince1604.•  January1987:– 15MsunBlueSupergiantStarSK‐69o202ExplodedintheLargeMagellanicCloud.

– Sawapulseofneutrinos,thentheblast.– Con&nuedtofollowitforthelastdecade.

•  Wealthofinforma&ononsupernovaphysics.

Nucleosynthesis

•  StartwithHydrogen&Helium:– FuseHydrogenintoelementsuptoIron/Nickel

– Theseaccumulateinthecorelayersofstars.

•  SupernovaExplosion:– “explosive”nuclearfusionbuildsmorelightelementsuptoIron&Nickel.

–  fast&slowneutronreac&onsbuildIron&Nickelintoheavyelementsupto254Cf

TopTenMostAbundantElements• 10)Sulfur• 9)Magnesium• 8)Iron• 7)Silicon• 6)Nitrogen• 5)Neon• 4)Carbon• 3)Oxygen• 2)Helium

• 1)Hydrogen

SupernovaRemnants

•  Whathappenstotheenvelope?– Enrichedwithmetalsintheexplosion

– Expandsatafew×10,000km/sec

•  SupernovaBlastWave:– Plowsupthesurroundinginterstellargas– Heats&s&rsuptheinterstellarmedium

– HotenoughtoshineasionizednebulaeuptoafewthousandyearsaYertheexplosion

Stardust

•  Metal‐enrichedgasmixeswithinterstellargas– Nextgenera&onofstarsincludesthesemetals.– Successivegenera&onsaremoremetalrich.

•  Sun&planets(&us):– Containmanymetals(iron,silicon,etc.)– Only~5Gyrold

•  TheSolarSystemformedfromgasenrichedbyapreviousgenera&onofmassivestars.

CygnusLoop:ScrapsofanoldSupernovaRemnant

Summary:

•  EndoftheLifeofaMassiveStar:– BurnHthroughSiinsuccessivecores– FinallybuildamassiveIroncore.

•  Ironcorecollapse&corebounce•  SupernovaExplosion:– Explosiveenvelopeejec&on– Mainsourcesofheavyelements

Ques&ons:

•  WheredidelementslikeU,Th,Pb,Au,Ag,etc.comefrom?

•  WheredidC,O,N,etc.comefrom?

•  HowdidallthatgetmixedupintheSun?

•  DoSupernovaes&llexplodeintheUniverse?•  WhatwouldhappenifaSnexplodedneartheEarth?