Core Helium Double Shell Burning The star is

Core Helium Double Shell Burning • The star is burning helium to oxygen and carbon • • • It doesn’t produce much energy – helium gets used • up fast • • • Eventually, helium is completely used up and we • have a carbon/oxygen core left • – 50 Myr for the Sun • • The star enters double shell-burning Molecular Cloud Protostar Main Sequence Red Giant Core Helium-Burning Double Shell-Burning Planetary Nebula White Dwarf

Double Shell Burning • The core consists of carbon/oxygen ash – It grows more massive over time • Heat is leaking out of it – It gets smaller and hotter • Helium and Hydrogen burning accelerate – Lots of energy dumped in outer layers – Star gets big, cool, and luminous – Bye bye Venus and maybe Earth • Star gets brighter than ever • Up and to the right again on H-R diagram • • Molecular Cloud Protostar Main Sequence Red Giant Core Helium-Burning Double Shell-Burning Planetary Nebula White Dwarf

Core Helium- Double-Shell Burning Core Double Helium. Shell. Burning • • 75. Double Shell Burning Name Molecular Cloud Protostar Main Sequence Red Giant Core Helium-Burning Double Shell-Burning Planetary Nebula White Dwarf Hydrogen Helium Carbon/Oxygen

Double Shell Burning Double Shell. Burning Core Helium. Burning • Star moves up and right on H-R diagram • • Molecular Cloud Protostar Main Sequence Red Giant Core Helium-Burning Double Shell-Burning Planetary Nebula White Dwarf

Giant Stages – Mass Dependence • For stars from 0. 5 to 3 MSun, it is qualitatively the same – Heavy stars do everything faster • For heavier stars, some details are different – Higher temperature and lower density – Core isn’t so compact – No dramatic increase in luminosity • Motion on the H-R diagram is mostly horizontal – Stars get bigger and cooler, not brighter • • Molecular Cloud Protostar Main Sequence Red Giant Core Helium-Burning Double Shell-Burning Planetary Nebula White Dwarf

Giant Stages – Mass Dependence • • Molecular Cloud Protostar Main Sequence Red Giant Core Helium-Burning Double Shell-Burning Planetary Nebula White Dwarf

Giant Stages – Mass Dependence • • Core Helium-Burning Molecular Cloud Protostar Main Sequence Red Giant Core Helium-Burning Double Shell-Burning Planetary Nebula White Dwarf

Giant Stages – Mass Dependence • • Core Helium Burning Double Shell-Burning Molecular Cloud Protostar Main Sequence Red Giant Core Helium-Burning Double Shell-Burning Planetary Nebula White Dwarf

Mass Loss • During red giant and especially double shell-burning stage, star is huge and luminous – Gravity is weak at the surface • Dust particles form on surface – These absorb light very efficiently • Light pressure begins pushing surface away – Like solar wind, but much stronger • Star begins to quickly lose substantial mass • The inside is hardly affected, for a while – Hydrogen Helium Carbon/Oxygen • • Molecular Cloud Protostar Main Sequence Red Giant Core Helium-Burning Double Shell-Burning Planetary Nebula White Dwarf

Dying Stages – Low Mass Stars Planetary Nebula • As the outer layers are lost, inner layers gradually revealed – We see the inside of the star • Until nearly the end, the inside is unaffected – Still burning fuels at the same rate • • Molecular Cloud Protostar Main Sequence Red Giant Core Helium-Burning Double Shell-Burning Planetary Nebula White Dwarf Q. 76: Planetary Nebula on H-R diagram

Planetary Nebula on H-R Diagram Double Shell. Burning Core Helium. Burning • Star moves to left on H-R • • Molecular Cloud Protostar Main Sequence Red Giant Core Helium-Burning Double Shell-Burning Planetary Nebula White Dwarf

Planetary Nebula • Star becomes so hot it radiates in ultraviolet – Visible luminosity goes down • Ultraviolet light bumps electrons up in gas surrounding the star – Electrons fall back down – make visible light colors Q. 77: Planetary Nebula Spectrum • • Molecular Cloud Protostar Main Sequence Red Giant Core Helium-Burning Double Shell-Burning Planetary Nebula White Dwarf

Double Shell Burning White Dwarf Double Shell. White Planetary Dwarf Burning Nebula • • Molecular Cloud Protostar Main Sequence Red Giant Core Helium-Burning Double Shell-Burning Planetary Nebula White Dwarf Hydrogen Helium Carbon/Oxygen

Planetary Nebulae Abell 39

Planetary Nebulae Ring NGC 6751

Planetary Nebulae Eskimo Hourglass

Planetary Nebulae Helix NGC 2440 Dumbbell

Planetary Nebulae Egg

Planetary Nebulae M 2 -9 Cat’s Eye Spirograph

White Dwarfs • Burnt out Carbon/Oxygen core • Gradually cools and fades • • Molecular Cloud Protostar Main Sequence Red Giant Core Helium-Burning Double Shell-Burning Planetary Nebula White Dwarf Q. 78: Why Can’t You Walk Through Walls?

Degeneracy Pressure • Quantum mechanics – Certain types of particles: can’t have two of same type in same place – Electrons, neutrons, protons • When you push them together, you get pressure – Greatest for electrons P n 5/3/m • It is independent of temperature – As white dwarf cools, no change in size • White dwarf has constant radius, falling temperature • • Molecular Cloud Protostar Main Sequence Red Giant Core Helium-Burning Double Shell-Burning Planetary Nebula White Dwarf Q. 79: White Dwarf on H-R diagram

White Dwarfs Double Shell. Burning Core Helium. Burning • Star moves to right and down on H-R • • Molecular Cloud Protostar Main Sequence Red Giant Core Helium-Burning Double Shell-Burning Planetary Nebula White Dwarf

White Dwarf Size and Mass • Stars have lost mass – Sun will end as about 0. 6 MSun – 8 MSun will end as about 1. 4 MSun • The more massive they are, the smaller they are – Very dense! – Very small! (Earth sized) • Maximum mass - Chandrasekhar mass is 1. 4 MSun. • Any starting with > 8 MSun cannot end as a white dwarf • • Molecular Cloud Protostar Main Sequence Red Giant Core Helium-Burning Double Shell-Burning Planetary Nebula White Dwarf

White Dwarf Size and Mass • • Molecular Cloud Protostar Main Sequence Red Giant Core Helium-Burning Double Shell-Burning Planetary Nebula White Dwarf

Initial vs. Final Size • • Molecular Cloud Protostar Main Sequence Red Giant Core Helium-Burning Double Shell-Burning Planetary Nebula White Dwarf

White Dwarf Size • • Molecular Cloud Protostar Main Sequence Red Giant Core Helium-Burning Double Shell-Burning Planetary Nebula White Dwarf

H-R tracks for White Dwarfs

Summary of Stages: < 8 Solar Masses Double Shell. Burning Core Helium. Burning

Summary of Stages: < 8 Solar Masses Stage Molecular Cloud Protostar Main Sequence Red Giant Core Helium-Burning Double Shell-Burning Planetary Nebula White Dwarf Core Activity (not a star) Hydrogen burning Helium ash Helium burning Carbon/Oxygen ash (not a star) Dead C/O core Size Huge Large Small Large Medium Large Huge Tiny Surface Temp. Cool Hot