Main Sequence Red Giant

Main Sequence Red Giant•At the center, Hydrogen is gone – there is only Helium “ash”•As more Helium accumulates, gravity pulls the core together – it shrinks and heats up•Hydrogen continues to burn in a layer around the center

•High temperature – it burns fast•Luminosity rises

•This dumps lots of heat into the outer layer•It expands and cools

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

Giant Stages – Low Mass Stars

HydrogenHelium

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

Main SequenceRed Giant

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

•Star moves up and right on H-R diagram

Core Helium-Burning

Double Shell-Burning

Red Giant•The star is incredibly bright and incredibly large

•Goodbye Mercury•It is using up fuel faster than ever

•It evolves fast•200 Myr for Sun

•The core keeps getting more massive, more compressed, and hotter

•It accelerates faster and faster


An Aside: Some Nomenclature Issues•Astronomers use different names for the same thing•My old tests, and occasional diagrams, use alternate names:

New Names: Old Names:Core Helium-Burning Horizontal BranchDouble Shell-Burning Asymptotic BranchMassive Star Supernova Type II SupernovaWhite Dwarf Supernova Type I Supernova

More Nuclear Physics•There are other processes besides Hydrogen burning•At 100 million K, three Heliums can join to make carbon plus a little energy

3He C + Energy•With a little higher temperature,they can add one more to makeoxygen

C + He O + Energy

•These processes produce farless energy than hydrogen burning

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

•At 100 million K, the helium core in a red giant star ignites

•Suddenly for light stars (< 3 MSun)

•Gradually for heavy stars (> 3 MSun)•New heat source in core

•It expands and cools•Hydrogen, still burning in a shell, burns more slowly now

•Less heat going into hydrogen envelope•Hydrogen envelope shrinks and heats up

•Star moves down and left on H-R diagram

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

HeliumCarbon/Oxygen

Red GiantCore Helium- Burning

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

•Star gets hotter and dimmer

Core Helium-Burning


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

•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

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


Core Helium- Burning

Double Shell- Burning

Core Helium- Double-Shell Burning

HydrogenHeliumCarbon/Oxygen


Double Shell Burning

•Star moves up and right on H-R diagram


Core Helium-Burning


Giant Stages – Mass dependance•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



Giant Stages – Mass dependance


Giant Stages – Mass Dependence

Core Helium-Burning


Giant Stages – Mass Dependence


Core Helium Burning

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


Main Sequence Red Giant

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