Stellar Life Stages

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. 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. 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