The Death of Stars - I.

Transcription

1 Th Dath of Stars - I.

2 Larning Objctivs! B abl to sktch th H-R diagram and includ stars by siz, sctral ty, liftim, color, mass, magnitud, tmratur and luminosity, rlativ to our Sun! Comar Rd Dwarfs to our Sun in trms of thir diffrnt masss and intriors! Know th hysics of th volution of low mass stars from Main Squnc to whit dwarf (fusion, gravity, collas, xansion, tmratur, comosition, quilibrium)! How do volving stars mov around th H-R diagram (whr do thy go whn xanding, hlium burning tc?)! How dos lctron dgnracy rssur stabiliz a dad star? What is a whit dwarf? What is a lantary nbula?

3 Imortant bad drawing So much information in th HR diagram...

4 Th Evolution of Stars! A star s volution dnds on its mass! W will look at th volution of thr gnral tys of stars! Rd dwarf stars (lss than 0.4 M )! Low mass stars (0.4 to 8 M )! High mass stars (mor than 8 M )! W can track th volution of a star on th H-R diagram! From Main Squnc to giant/surgiant and to its final dmis

5 Rd Dwarf Stars! 0.08 M < Mass < 0.4 M! Fully convctiv intrior (no radiativ zon )! Burn hydrogn slowly as convction constantly circulats hydrogn to th cor! Liv 100s of billions to trillions of yars! Th Univrs is only 13.8 billion yars old, so non of ths stars hav did yt

6 Stllar Dmis! Low mass star Hlium-burning rd giant Whit dwarf and lantary nbula High mass star Hlium-burning rd surgiant Othr surgiant hass Cor-collas surnova

7 Path of a Solar-Mass (1 M ) Star Plantary nbula Asymtotic giant branch Hlium flash Horizontal branch Rd giant Protostar Whit dwarf Main squnc

8 Lif of a Low Mass Star Main squnc Cor hydrogn burning T cor ~ 15 million K Rd giant Shll hydrogn burning Asymtotic branch giant Shll hlium burning Hlium flash Horizontal branch Cor hlium burning T cor ~ 100 million K

9 Hydrostatic Equilibrium! Th battl btwn Gravity and Prssur! Prssur from fusion ushs out and gravity ulls in an quilibrium! This is why a Main Squnc star isn t shrinking vn though it s a big ball of gas! A Main Squnc star s lif is all about this battl

10 Th Rd Giant Phas! Whn th hydrogn is gon in th cor, fusion stos! Th cor starts to contract undr its own gravity! This contracting hats aras of th star nar th cor, and hydrogn fusion starts in a shll around th cor! Th ush from fusion in this shll xands th star! As th star xands, its surfac movs farthr from th cor and it cools so it bcoms a rd giant

11 Path of a Solar-Mass (1 M ) Star Plantary nbula Asymtotic giant branch Hlium flash Horizontal branch Rd giant Protostar Whit dwarf Main squnc

12 Th Horizontal Branch! Whn th cor rachs 100 million K, it can start to fus hlium into carbon! this stabilizs th cor! Th star shrinks slightly and th surfac hats u! 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

13 Path of a Solar-Mass (1 M ) Star Plantary nbula Asymtotic giant branch Hlium flash Horizontal branch Rd giant Protostar Whit dwarf Main squnc

14 Whn Th Hlium Runs Out! Fusion in th cor stos th hlium has bn convrtd to carbon and oxygn! This is whr carbon and oxygn in our univrs com from!! Evry carbon atom in your body is th rmnant of a dying star! Th star s cor collass undr its own gravity! A shll nar th cor starts to fus hlium and th star xands and cools (again). Th star is now calld an asymtotic giant branch (AGB) star

15 Path of a Solar-Mass (1 M ) Star Plantary nbula Asymtotic giant branch Hlium flash Horizontal branch Rd giant Protostar Whit dwarf Main squnc

16 End Gam! Th outr layrs of th AGB star ar cast off! U to 80% of th star s original mass! Th cor rmains, mad of carbon and oxygn from hlium fusion! Th cor is vry hot, abov 200,000 K NGC 2440! Ultraviolt radiation from th cor ionizs th cast off outr layrs! Th star bcoms a lantary nbula T > 200,000 K

17 Plantary Nbula

18 What About th Cor?! Nuclar fusion has stod, and gravity bgins to win th battl! Th cor contracts to th siz of th Earth!But it s about 60% of th Sun s mass!matrial in th cor is comrssd to a dnsity of 1,000 kg/cm 3! Th star nds its lif as a whit dwarf!it slowly cools off ovr billions of yars

19 Path of a Solar-Mass (1 M ) Star Plantary nbula Asymtotic giant branch Hlium flash Horizontal branch Rd giant Protostar Whit dwarf Main squnc

20 What stos a whit dwarf from contracting furthr?! A quantum ffct: lctron dgnracy rssur! Th lctrons ar squashd togthr towards a quantum limit that is unhysical! This crats rssur to countract gravity! Which stos th contraction SQUEEZE Mattr in th cor of a normal star Elctron-dgnrat mattr 1 ton r cubic cm

21 Rlativ Siz of a Whit Dwarf 12,000 km An uttrly insignificant littl blu-grn lant Whit dwarf wighs about 0.6 M

22 Whit Dwarfs!

23 Nxt Tim Th Dath of Stars II