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30.2 Stellar Evolution
Stellar Evolution
Section 30.2
Hertzsprung-Russell Diagram
· Hertzsprung & Russell noticed that the higher a star's
temperature, the more energy it gave off per
second (luminosity)
· developed a graph to show the relationship
· most stars fit in a diagonal band that runs from the
upper left (hot, blue, bright stars) to the lower right
(cool, red, dim stars)
called the main
sequence
90% of all stars are
main sequence stars
Hertzsprung-Russell Diagram
· white dwarfs
small, hot, dim
· red giants
large, cool
· red supergiants
largest, cool stars
2 According to the diagram, what are
the characteristics of Sirius B?
A
bright, hot
B
bright, cool
C
dim, hot
D
dim, cool
1 Use the H-R Diagram to determine
which star is the hottest and brightest.
A Sirius B
B
Spica
C
Sirius
D
Proxima
Centauri
Star Formation
· nebula - beginning of a star
cloud of gas and dust that was once in other stars
gravity pulls particles closer together and the
nebula condenses
· protostar - star fetus
temperature increases
· nuclear fusion makes
the birth of a star
30.2 Stellar Evolution
Stellar Equilibrium
· gravity pushes in
· fusion produces heat and pressure that push out
· in = out and stars are able to maintain a stable size
not true in later life
3 What event marks the birth of a star?
A
stellar equilibrium
B
nuclear fusion ends
C
supernova explosion
D
nuclear fusion begins
Giant vs. Supergiant
· 3rd stage
· almost all hydrogen has been turned into helium
· stars starts to collapse
increases the core
temperature
hydrogen fusion causes the star to
expand rapidly
stars begin to cool
· sun-like stars become red giants
· stars bigger than the sun become red supergiants
Main-Sequence Stage
· 2nd and longest stage
· nuclear fusion of hydrogen into helium produces
energy
· when fusion slows or stops, stars move off the main
sequence
· next stage is determined by a star's size
4 How do main sequence stars generate
energy?
A
nuclear fusion; helium to hydrogen
B
nuclear fusion; carbon to hydrogen
C
nuclear fusion; hydrogen to carbon
D
nuclear fusion; hydrogen to helium
Final Stages of Sun-like Stars
· planetary nebula
cloud of gas around a
star that is dying
· white dwarf
small, hot, dim star that
is the leftover center
of an old star
becomes a black dwarf
when it stops emitting
light
end of many sun-like
stars
30.2 Stellar Evolution
· nova
Nova vs. Supernova
star that suddenly becomes brighter
captures gases from a nearby red giant increasing
the pressure inside a white dwarf and causes an
explosion
can be a nova several times
Sun-like Star Evolution Summary
· nebula
protostar
sun-like star
planetary nebula
white dwarf
red giant
some go through nova/supernova stage
most become black dwarfs and disappear
· supernova
violent explosions that destroy the white dwarf and
much of the red giant
5 A large, bright star whose hot core has
used up most of its hydrogen is a
A
giant
B
nova
C
supernova
D
planetary nebula
Final Stages of Massive Stars
· massive = 8 or more times bigger than the sun
· supernovas
next step: neutron star or black hole
· neutron star - very small but incredibly dense ball
of neutrons
pulsars - neutron stars that emit radio waves
· black hole - an object so massive and dense that
even light cannot escape its gravity
6 What is the lifecycle of a sun-like star?
1 - nebula
2 - planetary nebula
3 - protostar
4 - red giant
5 - sun-like star
6 - white dwarf
Massive Star Evolution Summary
· nebula
protostar
massive star
red
supergiant
supernova
neutron star or black
hole
30.2 Stellar Evolution
7 MATA: After massive stars become
supernovas they turn into
A
white dwarfs
B
neutron stars
C
black holes
D
black dwarfs