Transcript Ch. 26.3: Low and Average Mass Stars

Ch 26.2 & 3
Life Cycle of Average & Low Mass Stars
1. What are the stages of star low and
average mass stars?
2. How does the star’s composition change
as it ages (Think fusion)?
3. How does the star’s size, density,
brightness, and temperature change as it
ages?
Stars form
from clouds of
dust & gas.
•Gravity pulls
nebula into a
core.
•Temps
increase to
millions of
degrees
NUCLEAR
FUSION begins!
A star is born!
•Small, cool, dim
•Lasts 100 billion years (fuses slowly)
• Brighter & hotter
•Lasts for 10 billion years
•Expanded
•Bright (big)
•Cool
•Unstable (core
contracting while
shell expands)
•Helium fusion in
core; Hydrogen
fusion in outer
layers
Our sun would take up the orbits of Venus … maybe Earth
When RED GIANT
has iron in core
 fusion stops &
the star collapses
WHITE DWARFS
Small
Dense
Dim
Hot
Dying
Planetary
Nebula = ring
of gas cast
off by outer
layer of Red
Giant before
collapsing.
Dim because no real fusion going on. Hot due to residual heat
(Why embers of a fire are hot after fire is put out).
•No more Fusion
•Dead Star
Not really a Black
Dwarf
•Dense
•Dark
•Cold
Without fusion, there is no thermal pressure pushing out. Gravity pulls the star
into its own center – collapsing it to an Earth-sized core.
Ch 26.3 Check Up
1. How is a protostar different from an actual star?
2. What element is being fused in the core of young stars?
Red Giants?
3. How is a star’s mass related to the length of its life
cycle? Give an example
4. What are 3 possible end stages for stars (depending on
mass)?
5. Which choice best compares a blue star to a yellow star
on the main sequence?
a. Blue stars are cooler and last longer than yellow
stars.
b. Blue stars are hotter and last longer than yellow
stars.
c. Blue stars are cooler and “live” shorter lives.
d. Blue stars are hotter and live longer lives.