Astronomy 210. Outline. Life of a Low Mass Star. Evolutionary Path of a Solar-Mass Star. Solar Observing & HW9 due Friday Stardial 2 is available.

Transcription

1 Astronomy 210 Outlin This Class (Lctur 32): Lif and Dath of th Sun Nxt Class: Lif and Dath of Othr Stars Solar Obsrving & HW9 du Friday Stardial 2 is availabl. Dath of a solar mass star! Burning m u. Whit dwarfs. Th story of mor massiv stars. Surnova! Music: Amy Hit th Atmoshr Counting Crows Evolutionary Path of a Solar-Mass Star Lif of a Low Mass Star Plantary nbula Asymtotic giant branch Horizontal branch Rd giant Hlium flash Protostar Main squnc Cor hydrogn burning T cor ~ 16 million K Hlium flash Rd giant Shll hydrogn burning Asymtotic branch giant Shll hlium burning Whit dwarf Main squnc Horizontal branch Cor hlium burning T cor ~ 100 million K

2 Th Rd Giant Phas Whn th hydrogn is gon in th cor, fusion stos Cor starts to contract undr its own gravity This contracting hats th cor, and hydrogn fusion starts in th shll around th cor Enrgy is rlasd, xands nvlo Lum incrass! As th nvlo xands, it cools so it bcoms a rd giant Contraction Junction In cor, contraction incrass ρ Contraction slowd by Pauli xclusion rincil: can't ut 2's in sam stat Quantum dgnracy rssur (sam as in solid bodis!) P = Kρ 5/3 K const: dnds only on ρ, not T ( idal gas!) Contraction Junction Hlium Burning Dgnrat cor and H burning shll Cor hats H fusion ignits In a normal gas: T, P so it xands & cools In a dgn. gas: T, P const so no xansion & no cooling So th raction sds u xlosion! Hlium Flash (fw min) Not: xlosion nrgy trad in outr layrs so don't s anything scial from th outsid Whn th cor of th star rachs 100 million dgrs, it can start to fus hlium (th ash of hydrogn burning) into carbon Calld th Tril-Alha Procss Convrts 3 hliums into on carbon + nrgy

3 Th Horizontal Branch Hlium burning stabilizs th cor Th outr nvlo shrinks, hats u, and dims slightly But hlium dosn t last vry long as a ful Horizontal branch liftim is only about 10% that of a star s main squnc liftim Our Sun will burn hlium for about a billion yars Also H burning is unstabl Chid Variabls Giants with mor than 5 M Sun ntr riods of variability as thy volv Bcom unstabl Start to ulsat at a rgular ac Pulsation maks thm vary in brightnss Th riod of ulsation is rlatd to th star s absolut magnitud Excllnt way to masur distanc! Whn Hlium Runs Out Fusion in th cor stos th hlium has bn convrtd to carbon and oxygn Stllar cor collass undr its own gravity Shll starts fusing hlium Star starts to grow and cool again Calld th asymtotic giant branch Evolutionary Path of a Solar-Mass Star

4 Evolutionary Path of a Solar-Mass Star End Gam Surwind Outr layrs of th rd giant star ar cast off T > 200,000 K U to 80% (at last 50%) of th star s original mass Th cor rmains, mad of carbon/oxygn ash from hlium fusion Th cor is vry hot, abov 200,000 K Ultraviolt radiation from th cor ionizs th cast NGC 2440 off outr layrs Bcoms a lantary nbula Unfortunat nam, but som of th most bautiful objcts in th sky. Plantary Nbula Plantary Nbula Not th mission lins vibrant colors (somwhat nhancd) Ring: arox tru color, H=blu, O=grn, N=rd Cat's y: H=rd, O=blu, N=grn Also not: rarly shrical: rotation, mag filds, jctd gas, and comanion can all mak axial Ring Nbula Cat s Ey Nbula

5 What About th Cor? Nuclar fusion has stod, and gravity bgins to win th battl Cor contracts to th siz of th Earth But its about 60% th Sun s mass! Matrial in th cor is comrssd to a dnsity of 1,000 kg/cm 3! Vry hot, surfac tmratur >100,000 K Final fat - Whit dwarf Slowly cools off ovr billions of yars Elctron Dgnracy Th lctrons gt so squashd togthr that thy gt ushd into dgnrat stats This crats rssur to countract gravity (Pauli xclusion) Stos contraction Mattr in th cor of a normal star Elctron-dgnrat mattr 1 ton r cubic cm Elctron Dgnracy Elctron Dgnracy: LD Th quation of stat is: P = Kρ γ γ = 5/3 low dnsity γ = 4/3 high dnsity ρ» 10 9 kg/m 3 From HW 9, w know that P GM 2 /R 4 And from abov γ 3 P= Kρ K( M / R ) thn γ γ = 5/3 low dnsity Th radius only dnds on Mass! Th highr th mass, th smallr th whit dwarf! R M (1/ 3)

6 Elctron Dgnracy: HD Chandraskhar limit γ = 4/3 high dnsity K M G 3 2 Th mass is indndnt of radius or dnsity! Numrically, this valu is M = 1.4 M Also calld th Chandraskhar limit! Maximum mass of a whit dwarf. No whit dwarf obsrvd is ovr this. If mass is highr, th whit dwarf can not suort itslf with lctron dgnracy, and it collass mor! Gravity! Rlativ Siz of Whit Dwarf Whit Dwarvs! 12,000 km Whit dwarf but will usually wigh about 0.6 Solar masss

7 Stllar Diamonds!?! Th intrior of th whit dwarf crystallizs du to th xtrm rssurs Mad mostly of carbon (som oxygn) Crystallizd carbon = a diamond With a blu-grn tint from th oxygn 10 billion trillion trillion carats! Th Lif and Tims of a Low-Mass Star htt://rainman.astro.uiuc.du/ddr/stllar/bginnr.html Binary Systms? In a clos binary air of stars with slightly diffrnt masss, th highr mass star volvs into a whit dwarf first Latr, th othr star volvs into a rd giant Whit dwarf thn stals mass from its giant comanion! Crats a dns layr of hydrogn gas on th whit dwarf s surfac Nova If nough matrial ils u onto th surfac of a whit dwarf, can undrgo xlosiv nuclar fusion Whit dwarf blows off this nvlo and brightns by tims Fads ovr a riod of months This is calld a nova (from Latin for nw ) Common, about 20 r yar in our galaxy Stoln hydrogn layr Whit dwarf (carbon-oxygn) Nova Cygni 1992

8 Main Squnc Mass Rlation High mass Lif Fast, Di Young High-mass stars: gas guzzlrs Vry bright Consum hydrogn ful suly vry quickly Only liv for millions of yars on th main squnc Low mass And whn th Hydrogn Runs out? Similar to lowr-mass stars in th first fw stags Whn th hydrogn suly runs out th cor starts to contract Hydrogn shll burning (around th hlium cor) starts Th outr nvlo xands quickly bcoming a rd surgiant Cor collass Th Surgiant Phas Outr nvlo of th star grows largr and coolr U to 5 AU in siz! Unlik a low mass star, brightnss dos not incras dramatically Evntually, cor is hot nough that it can fus hlium atoms togthr (non dgn gas, so no flash) Star contracts and hats u Now a blu surgiant

9 Massiv Stars: Cycls of Fusion Hlium fusion is not th nd for massiv stars Cycls of cor contraction, hating, ignition Ash of on cycl bcoms ful for th nxt C+H O O+H N... U to iron Onion-skin lik structur dvlos in th cor Iron Th End of th Road Surgiants burn havir and havir atoms in th fusion rocss Each stag fastr than th last Aftr iron - no ful lft! It rquirs nrgy to roduc havir atoms Stag H fusion H fusion C fusion N fusion Tmratur 40 million K 200 million K 600 million K 1.2 billion K Duration 7 million yr 500,000 yr 600 yr 1 yr O fusion Si fusion 1.5 billion K 2.7 billion K 6 mo 1 day Valus for a 25M Sun Astronomy star 210 Sring 2005 Evolutionary Path of a High-Mass Star Cor Collas Main squnc Surnova Blu surgiant Carbon ignition Rd surgiant Hlium ignition Th iron cor of th star is suortd by lctron dgnracy rssur Sam rssur that suorts a whit dwarf Evntually, gravity will win This will han whn th cor rachs 1.4 solar masss Whn it gos ovr th limit cor collas! From 1,000 km across to 50 km in 1/10th of a scond Narly 10% sd of light! Th cor is transformd into a sa of nutrons Elctrons ar squzd into rotons, nutrinos rlasd

10 Whn Elctron Dgnracy Just Isn t Enough Mattr in th cor of a normal star n n n n n n n n n n n n n n n n n n n n n n n n Nutron-dgnrat mattr 100 million tons r cubic cm Elctron-dgnrat mattr 1 ton r cubic cm ν ν ν Nutrinos roducd as lctrons ar forcd into nucli Surnova! During collas, art of th cor rbounds and roducs a shock wav Matrial is so dns, that it is oaqu to th nutrinos roducd Nutrinos giv th shock a kick Ris th outr layrs of th star aart Star xlods in a surnova Rlass a trmndous amount of nrgy 99% of th nrgy in th form of nutrinos Surnova! Bright as a Galaxy Surnova ar bright A star s brightnss incrass 10,000 tims! Rivals an ntir galaxy! Light from a singl surnova Combind light of 100 billion stars