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