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Stellar Life StagesStar Birth and Death
Background info.
•Since early human history, people have looked up at the night sky in amazement.
•What is out there?
•What are stars?
•What are planets?
Background info.
•Ancient civilizations imagined that groups of stars formed pictures called constellations.
•Many constellations are named after animals or mythological characters.
Background info.
Orion, The Hunter
Background info...
Astronomers recognize
88 constellatio
ns
Birth of a Star
•stars are born in a nebula
•a nebula is a dark, cool cloud of dust and gas
•our galaxy has mostly hydrogen and a little helium gas
Horsehead Horsehead is a dark is a dark nebula in nebula in
front of the front of the pink pink
emission emission nebula.nebula.Horsehead Horsehead is about is about
1,600 light 1,600 light years away.years away.
•nebula becomes dense (thick and heavy) and starts to contract
•gravity squeezes dust particles to the center, gravitational energy changes into heat energy
HOT
draw this
Contracting Nebula
Protostar (developing)
•gravity squeezes for millions of years and temperature slowly rises
•when its hot enough it emits red light
•still too cool for nuclear fusion...
ProtostarProtostar
•contraction continues and the core reaches up to 10 million Kelvins
•pressure in the core is high enough for nuclear fusion to start and a star is born
•nuclear fusion: when atomic nuclei join together to form a heavier nucleus, energy is released, aka nucleosynthesis
draw this
Nuclear Fusion
the sun the atomic bomb
•heat from hydrogen fusion causes gas pressure inside the star to increase
Gas molecules are Gas molecules are always moving in always moving in random directions.random directions.What happens to What happens to them when gravity them when gravity pushes down?pushes down?What happens when What happens when the temp. increases?the temp. increases?
•when pressure inside balances with pressure outside, it is called a main-sequence star
Gas Gas PressurePressure
Main SequenceStar
GravityGravity
Balance ofBalance of two forcestwo forces
draw this
Main-Sequence Star
•hydrogen fusion continues for billions of years until it runs out of hydrogen
•stable stars like our sun will burn hydrogen for about 10 billion years
•our sun is about 5 billion years old
Main Sequence Stars Main Sequence Stars
Red Giants•hydrogen fusion in the core ends
and the core contracts (gravity)
•hydrogen fusion still occurs in the outer layers and they expand
•surface temp. cools and turns red but the core stays hot and changes helium into carbon (nucleosynthesis!!!)
Red Giant
Burnout and Death
•all stars eventually run out of fuel and collapse
•low-mass stars and medium mass stars use up their hydrogen and collapse into a white dwarf
...the fate ...the fate of a star of a star depends depends
on its masson its mass
Massive Death•massive stars explode in a
supernova, debris is ejected as stardust...eventually gravity pushes it in
•dying stars that use up hydrogen produce helium (fusion), over time helium fuses to become heavier elements like lithium through iron (nucleosynthesis)
•black holes are remains of massive stars that have exploded, they are hot, dense and have strong gravity
•when matter is pulled into it, the matter disappears forever
Bend light around themNot even light can escape
Stellar Evolution
(look at page 710)
60 second summary
Review #1 Where are stars born?
• nova
• nebula
• nuclear fusion
• hollywood
๏ nebula
Review #2 What happens to a
nebula?• gravity pushes out and it gets
cold
• gravity only pushes out
• gravity pushes in and it gets hot
• gravity only pushes in
๏ gravity pushes in and it gets hot
Review #3 When a nebula is hot and
enough pressure is present, what happens next?•nuclear combustion
•nuclear fission
•nuclear fusion
•nuclear expansion
๏nuclear fusion
Review #4 What type of star is our
sun?•protostar
•main sequence star
•red giant
•white dwarf
๏main sequence star
Review #5What is the next life stage
for the sun?
•nebula
•nova
•red giant
•black hole
๏red giant
Review #6 How do massive stars die?
•in a nova or supernova
•in a nebula
•in a circle
•in a pulsar
๏in a nova
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