Giant Stages – Low Mass Stars Main Sequence  Red Giant

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Giant Stages – Low Mass Stars
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 HeliumBurning
•Double ShellBurning
•Planetary Nebula
•White Dwarf
Main Sequence  Red Giant
Main
Red Giant
Sequence
Hydrogen
Helium
•Molecular Cloud
•Protostar
•Main Sequence
•Red Giant
•Core HeliumBurning
•Double ShellBurning
•Planetary Nebula
•White Dwarf
Red Giant
Double ShellBurning
Core HeliumBurning
•Star moves up and right on H-R diagram
•Molecular Cloud
•Protostar
•Main Sequence
•Red Giant
•Core HeliumBurning
•Double ShellBurning
•Planetary Nebula
•White Dwarf
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
•Molecular Cloud
•Protostar
•Main Sequence
•Red Giant
•Core HeliumBurning
•Double ShellBurning
•Planetary Nebula
•White Dwarf
An Aside: Some Nomenclature Issues
•Astronomers use different names for the same thing
•My old tests, and occasional diagrams, use alternate names:
New Names:
Core Helium-Burning
Double Shell-Burning
Massive Star Supernova
White Dwarf Supernova
Old Names:
Horizontal Branch
Asymptotic Branch
Type II 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 make
oxygen
C + He  O + Energy
•These processes produce far
less energy than hydrogen burning
Red Giant  Core Helium Burning
•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
•Molecular Cloud
•Protostar
•Main Sequence
•Red Giant
•Core HeliumBurning
•Double ShellBurning
•Planetary Nebula
•White Dwarf
Red Giant  Core Helium Burning
•Molecular Cloud
Red
CoreGiant
Helium- •Protostar
Burning •Main Sequence
•Red Giant
•Core HeliumBurning
•Double ShellBurning
•Planetary Nebula
Hydrogen
•White Dwarf
Helium
Carbon/Oxygen
Core Helium Burning
Double ShellBurning
Core HeliumBurning
•Star gets hotter and dimmer
•Molecular Cloud
•Protostar
•Main Sequence
•Red Giant
•Core HeliumBurning
•Double ShellBurning
•Planetary Nebula
•White Dwarf
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 HeliumBurning
•Double ShellBurning
•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 HeliumBurning
•Double ShellBurning
•Planetary Nebula
•White Dwarf
Core Helium-  Double-Shell Burning
•Molecular Cloud
Core
Double
HeliumShell- •Protostar
Burning
Burning •Main Sequence
•Red Giant
•Core HeliumBurning
•Double ShellBurning
•Planetary Nebula
Hydrogen
•White Dwarf
Helium
Carbon/Oxygen
Double Shell Burning
Double ShellBurning
Core HeliumBurning
•Star moves up and right on H-R diagram
•Molecular Cloud
•Protostar
•Main Sequence
•Red Giant
•Core HeliumBurning
•Double ShellBurning
•Planetary Nebula
•White Dwarf
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
•Molecular Cloud
•Protostar
•Main Sequence
•Red Giant
•Core HeliumBurning
•Double ShellBurning
•Planetary Nebula
•White Dwarf
Giant Stages – Mass dependance
•Molecular Cloud
•Protostar
•Main Sequence
•Red Giant
•Core HeliumBurning
•Double ShellBurning
•Planetary Nebula
•White Dwarf
Giant Stages – Mass Dependence
Core Helium-Burning
•Molecular Cloud
•Protostar
•Main Sequence
•Red Giant
•Core HeliumBurning
•Double ShellBurning
•Planetary Nebula
•White Dwarf
Giant Stages – Mass Dependence
Core Helium Burning
Double Shell-Burning
•Molecular Cloud
•Protostar
•Main Sequence
•Red Giant
•Core HeliumBurning
•Double ShellBurning
•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 HeliumBurning
•Double ShellBurning
•Planetary Nebula
•White Dwarf
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