1. Stellar Life Stages
Star Birth and Death

2. 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?

3. Background info.
Ancient civilizations imagined that groups of stars formed pictures called constellations.
Many constellations are named after animals or mythological characters.

4. Background info.
Orion, The Hunter

5. Astronomers recognize 88 constellations
Background info...
Astronomers recognize 88 constellations

6. 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

7. Horsehead is a dark nebula in front of the pink emission nebula.
Horsehead is about 1,600 light years away.

8. nebula becomes dense (thick and heavy) and starts to contract
gravity squeezes dust particles to the center, gravitational energy changes into heat energy

9. Contracting Nebula
draw this
HOT

10. 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...

11. Protostar

12. 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

13. Nuclear Fusion
draw this

14. the sun
the atomic bomb

15. heat from hydrogen fusion causes gas pressure inside the star to increase
Gas molecules are always moving in random directions.
What happens to them when gravity pushes down?
What happens when the temp. increases?

16. when pressure inside balances with pressure outside, it is called a main- sequence star

17. Balance of two forces draw this Main Sequence Star Gravity Gas
Pressure
draw this
Balance of
two forces

18. 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

19. Main Sequence Stars

20. 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!!!)

21. Red Giant

22. 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

23. ...the fate of a star depends on its mass

24. 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)

25. 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

26. Bend light around them
Not even light can escape

27. Stellar Evolution
(look at page 710)

28. 60 second summary

29. Review #1 Where are stars born?
nova
nebula
nuclear fusion
hollywood

30. nebula

31. 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

32. gravity pushes in and it gets hot

33. Review #3 When a nebula is hot and enough pressure is present, what happens next?
nuclear combustion
nuclear fission
nuclear fusion
nuclear expansion

34. nuclear fusion

35. Review #4 What type of star is our sun?
protostar
main sequence star
red giant
white dwarf

36. main sequence star

37. Review #5What is the next life stage for the sun?
nebula
nova
red giant
black hole

38. red giant

39. Review #6 How do massive stars die?
in a nova or supernova
in a nebula
in a circle
in a pulsar

40. in a nova