Today’s outline

Review

High and low mass

Low-mass Stars Summary of evolution Main sequence Hydrogen Exhaustion Review: Clusters, Birth of Stars Giant phase Helium flash Horizontal Branch Evolution of low mass stars Helium Exhaustion Planetary Nebula I Low and high mass stars Summary again

I Interior of a giant star

I Phases of burning

I White dwarf formation Review

High and low mass

Low-mass Stars Summary of evolution Main sequence Evolution of low mass stars Hydrogen Exhaustion Giant phase I Low and high mass stars Helium flash Horizontal Branch Helium Exhaustion I Interior of a giant star Planetary Nebula Summary again I Phases of burning

I White dwarf formation Reference stars

Low Mass: Review I Sun - low-mass ”dwarf” High and low mass Low-mass Stars I Vega - low-mass ”dwarf” Summary of evolution Main sequence I Sirius - low-mass ”dwarf” Hydrogen Exhaustion Giant phase Helium flash I Arcturus - low-mass giant Horizontal Branch Helium Exhaustion I Sirius B - white dwarf (very small) Planetary Nebula Summary again

High Mass:

I Rigil - high-mass (blue) giant

I Betelgeuse - high-mass (red) giant High and low mass stars Black hole Review "high−mass" High and low mass Low-mass Stars (hydrogen burning) Neutron Star Summary of evolution Main Sequence Main sequence 8 Hydrogen Exhaustion Giants Giant phase

Protostar Helium flash Horizontal Branch "low−mass" Helium Exhaustion Planetary Nebula 2 White dwarf Summary again Birth Mass Time Stars generally classified by their end-of-life I Low mass – form white dwarf stars, no supernova I High mass – form neutron stars or black holes in supernova low mass – less than about 8 solar masses exact dividing mass is not well known and depends on composition High and low mass stars Black hole

"high−mass" Review

(hydrogen burning) Neutron Star Main Sequence High and low mass 8 Giants Protostar Low-mass Stars "low−mass" Summary of evolution 2 White dwarf Main sequence Hydrogen Exhaustion Giant phase Helium flash

Birth Mass Horizontal Branch Time Helium Exhaustion Lifetime increases with decreasing Planetary Nebula mass – higher mass stars live Summary again shorter time on the main sequence

Compact remnant stars: White Dwarf - Earth-size star Neutron Star - City-sized star Summary of low-mass star evolution

Review Major stages of evolution High and low mass Low-mass Stars 1. main sequence Summary of evolution – core hydrogen burning Main sequence Hydrogen Exhaustion Giant phase 2. red giant Helium flash – shell hydrogen burning Horizontal Branch Helium Exhaustion 3. horizontal branch Planetary Nebula Summary again – core helium burning 4. asymptotic giant – shell helium and hydrogen burning 5. white dwarf

Stars with mass above 2M go straight to core helium burning (skip first giant stage) Main sequence structure

Review Main sequence phase – High and low mass longest-lived stage Low-mass Stars Summary of evolution Main sequence Hydrogen Exhaustion I Stable fusion of hydrogen to Giant phase helium Helium flash Horizontal Branch Helium Exhaustion I Structure similar to sun – Planetary Nebula core, radiative zone, Summary again convection zone I convection zone larger for lower masses

Main sequence lifetime of Sun: 10 billion years Slightly lower mass stars have lifetimes longer than the age of the Universe (14 billion years) Hydrogen exhaustion, Giant formation

Review

High and low mass I As hydrogen runs out core core contracts and heats Low-mass Stars hydrogen Summary of evolution Using up of hydrogen in core Main sequence exhaustion I Hydrogen Exhaustion helium core forms inert helium core Giant phase formation Helium flash I Hydrogen shell burning Horizontal Branch Helium Exhaustion around helium core Planetary Nebula helium Summary again core I Shell burning very hot, high expansion fusion rate I High luminosity causes expansion (more surface area) I Large convection zone hydrogen More hydrogen consumed burning → grow mass of helium core shell → contract size of helium core → higher luminosity Red Giant Phase

Review

High and low mass

Low-mass Stars Summary of evolution Main sequence Hydrogen Exhaustion Giant phase Helium flash Horizontal Branch Helium Exhaustion Planetary Nebula Summary again

Giant can fill significant portion of solar system.

Grows larger as shell burning source produces energy at higher rate due to contraction. Helium flash

Review

High and low mass

Red giant branch ends with Low-mass Stars helium flash: Summary of evolution Main sequence Hydrogen Exhaustion I Helium burning is ignited Giant phase Helium flash in core Horizontal Branch Helium Exhaustion Re-establishes core Planetary Nebula I Summary again burning

I Reduces overall luminosity (not shell burning)

core helium burning Horizontal Branch – Core helium burning

Review Horizontal branch stars have High and low mass Low-mass Stars similar luminosities Summary of evolution Main sequence due to similar core properties Hydrogen Exhaustion Giant phase Helium flash Horizontal Branch Helium Exhaustion Planetary Nebula Summary again

core helium burning Different temperature due to various amounts of mass loss while red giant Helium exhaustion in core, Giant formation again

Review Helium core burning High and low mass Low-mass Stars I as helum is consumed, inert Summary of evolution Main sequence core is again formed Hydrogen Exhaustion Giant phase I now two shells sources form Helium flash Horizontal Branch I produce even more energy Helium Exhaustion helium shell Planetary Nebula Eventually combination of burning Summary again burning inert hydrogen carbon and mass loss uses up remaining shell core hydrogen burning Further contraction is halted by degeneracy, preventing further H C nuclear fusion He The carbon core is left as a white dwarf star Not to scale!! Planetary Nebula

Review

High and low mass The end of low mass stars like the sun Low-mass Stars Summary of evolution Main sequence Last mass ejection from giant star forms a ”planetary” Hydrogen Exhaustion Giant phase Helium flash nebula Horizontal Branch Helium Exhaustion Planetary Nebula Summary again

Heated by ultaviolet radiation from hot, newborn white dwarf star, (temperature near 40,000 K) Summary of evolution

Review

High and low mass Major stages of evolution Low-mass Stars 1. main sequence Summary of evolution Main sequence – core hydrogen burning Hydrogen Exhaustion Giant phase 2. red giant Helium flash Horizontal Branch – shell hydrogen burning Helium Exhaustion Planetary Nebula 3. horizontal branch Summary again – core helium burning 4. asymptotic giant – shell helium and hydrogen burning 5. white dwarf

Stars with mass above 2M go straight to core helium burning