1. Stars

2. Life cycle of star http://www.youtube.com/watch?v= H8Jz6FU5D1A http://www.youtube.com/watch?v= H8Jz6FU5D1A

3. http://aspire.cosmic- ray.org/labs/star_life/starlife_proto. html

4. 1. Nebula = cold, dark cloud of dust and gas [mostly H]

5. gravity pulls particles, to clump together

6. Accretion: accumulating more mass

7. Clumps increase in size [accretion] pressure and temperature increases [due to KE of particles]

8. 2. Protostar when forces are in equilibrium : gravity collapses particles together, high temperature/pressure pushes particles apart. At equilibrium Gas pressure = gravity

9. If protostar too small, becomes brown dwarf, never a real star.

10. 4. STAR If enough mass, critical temperature protostar core begins to fuse H into He : star is born.

11. The star is stable while the gravitation pulling the star together is balanced by the internal pressure pushing it apart.

12. During lifetime, stars fuse Hydrogen into Helium and then fuse helium into Carbon.

13. Massive stars can fuse carbon into heavier elements.

14. 3. Main sequence

15. 90% of stars spend majority of life on the Main Sequence

16. On the main sequence, hydrogen is fused into helium H is fused into He..

17. Main sequence is a grouping of stars by size, color, luminosity

18. We compare other stars to the brightness [luminosity ] of the Sun:

19. Temperature determines the color of a star TemperatureColor 30,000 - 60,000 KBlue stars 10,000 - 30,000 KBlue-white stars 7,500 - 10,000 KWhite stars 6,000 - 7,500 KYellow-white stars 5,000 - 6,000 KYellow stars (like the Sun) 3,500 - 5,000KYellow-orange stars < 3,500 KRed stars

20. Mass-luminosity relationship for Main Sequence Stars L = L o [M/M o ] 3.5 Lo = luminosity of Sun Mo = mass of Sun

21. The Herzsprung-Russell Diagram H-R diagram shows relationship of luminosity, temperature, size

22. [ H-R diagram]

23. Note the scales are log scales, not linear.

24. Mo is the mass of the Sun Low mass stars: 0.5Mo medium mass stars: 0.5Mo – 3Mo massive stars: >3 Mo

25. Larger, hotter stars burn out very fast - in a few million years. Smaller, cooler stars burn slowly for billions of years

26. The Sun is a medium yellow star. The surface temperature is about 6000K The Sun has a life expectancy of about 10 billion years

27. Try the interactive star lab: http://aspire.cosmic- ray.org/labs/star_life/starlife_seque nce.html http://aspire.cosmic- ray.org/labs/star_life/starlife_seque nce.html

28. Wh

29. After becoming red giant low mass stars [mass of Sun] shrink into white dwarfs. Radius is close to radius of Earth.

30. Medium mass stars [ 1.4 to 3 Mo] expand into Red Giants, collapse and then explode into a supernova

31. Finally becomes a neutron star [about the size of Manhattan]

33. Massive stars collapse and begin to fuse carbon. They explode as supernova and the core is crushed into a black hole.

34. After all H is fused, star leaves the main sequence.

35. Pressure increases, stars expand enormously and cool.

36. Small stars expands and sheds outer layers

37. Medium stars expand into red giants

38. After about 100,000 years the protostar has drawn in enough dust and gas to become a star.

39. When core temperature reaches 10 million degrees, H begins to fuse into He, releasing energy [heat]

40. Most stars are Main Sequence Stars

41. When core H has all fused to He,

43. About 1 million Earth’s fit in the Sun

44. http://www.youtube.com/watch?v= g4iD-9GSW-0

45. Sun compared to largest star

46. http://www.youtube.com/watch?v= Bcz4vGvoxQA

47. HR diagrams http://www.youtube.com/watch?v= Kqe6F-Qf9Tk http://www.youtube.com/watch?v= Kqe6F-Qf9Tk

48. Black hole swallows a star http://www.youtube.com/watch?v= O3Z5AS3TTS4 http://www.youtube.com/watch?v= O3Z5AS3TTS4