3. Main sequence Hydrogen Fusion: Inside the sun, 4 Hydrogen nuclei fuse to form 1 Helium nucleus, releasing light, heat and radiation.

4. Two Opposing Forces Pressure from Nuclear Reactions pushing outward Gravity pulling inward

5. Hertzsprung - Russell Diagram Main Sequence Stars Main sequence stars are “hydrogen-burners”. Going up to the left, stars get bigger and brighter and hotter, going from red hot to yellow hot to white hot to blue hot.

6. The mass of a star determines its fate Red Giant Supergiant Supernova White Dwarf Neutron Star Black Hole Supergiant Brown Dwarf Tiny Stars Sun-Sized Stars 3 – 10 M Stars 20 – 30 M Stars

7. The mass of a star determines its fate: 1.The smallest stars start out as red dwarf main sequence hydrogen burners, then become hotter, brighter stars called white dwarfs when they collapse and reheat to “burn” helium.

8. 2. Medium-sized stars such as our Sun burn very slowly. Our sun will burn for another 5 - 6 billion years, mostly as a yellow dwarf main-sequence hydrogen- burner, then collapse due to gravity. Evolution of sun-sized stars

10. Inside a Red Giant 2) Extra heat causes outer rim of hydrogen to billow out into space 1) Helium fuses to form Carbon and Oxygen at the Core

11. Sun vs. Red Giant

12. Betelgeuse in Orion 15 X as big as the sun Red Giant

13. Planetary Nebulae These clouds form as the red giant expands and cools.

14. Evolution of sun-sized stars

15. Sun vs. white dwarf 4. (cont.) A white dwarf is the size of Earth, but has the mass of the Sun…

16. Stars grow and shrink… Core begins runs out of H - Pressure drops. Gravity becomes greater than pressure. Core starts to shrinks to Earth-sized.

17. Stars grow and shrink…

18. White Dwarfs

19. White Dwarf at the center of a planetary nebula cloud

20. Evolution of sun-sized stars

21. 5. (cont.) (Our sun isn’t big enough to make the carbon core start any further fusion reactions.) Evolution of sun-sized stars

22. life cycle of a sun-sized star

23. Hertzsprung - Russell Diagram Main Sequence Stars Red Giants are very large but cool stars. The sun is medium sized and medium hot (yellow hot). White dwarfs are tiny but very hot (white hot - 10,000 o K).

24. Main Sequence – Next 5 billion years Red Giant – He-C reaction in core causes H to “flame out” at outer rim Red Giant cools to form Planetary Nebula Core of Red Giant shrinks rapidly… White Dwarf …to form a White Dwarf

25. The Fate of Massive Stars

26. Evolution of massive stars Larger stars ( 2 - 3 times the mass of the sun ), burn brighter and die more quickly in violent cosmic spasms called supernovas.

27. Evolution of massive stars 1. When the H and He fuel is burned up, gravity takes over just as it did in the smaller stars.

28. Evolution of massive stars Helium fuses to make many new elements (as large as Iron: Z = 26).

29. Layers of a Red-Supergiant…

30. …A Huge Element “Factory”

31. Evolution of massive stars 4. The iron core shuts down the nuclear reactions and the star collapses one final time. This final collapse of the core creates incredibly high temperatures ( 8 billion K ) which trigger a huge thermonuclear blast – a supernova.

32. Shock Waves Spread Upward

33. Evolution of massive stars 6. When the star explodes, the blast sends star bits and shock waves all through the surrounding galaxies.

34. Evolution of massive stars 6. (cont.) Elements of all shapes and sizes are formed and scattered as well. Supernova Remnant Cloud

35. Evolution of massive stars 7. In the core of the star, the pressure is so great that electrons are shoved into the nucleus, where they combine with protons to form neutrons.

36. Evolution of massive stars 8. All that remains after a supernova blows up is a dense, spinning ball of neutrons called a neutron star…

37. Evolution of massive stars 8. …& an expanding iridescent nebular cloud called a supernova remnant cloud (SRC).

38. Neutron Star…

39. Supernova Remnant cloud

41. Supernova Remnant crab Nebula 1054 A.D.

42. Supernova Remnant crab Nebula 1054 A.D.

43. Supernova and Remnant Nebula Supernova 1987A After Before

44. life cycle of massive stars

45. life cycle of stars

46. life cycle of a supernova star 3 to 10

47. Hertzsprung - Russell Diagram Main Sequence Stars Stars 3 - 10 X the mass of the sun.

48. Hertzsprung - Russell Diagram Main Sequence Stars Stars 3 – 10X the mass of the sun turn into Red Supergiants

49. life cycle of a supernova star red supergiant

50. A star explodes… red supergiant

51. Forming a neutron star… red supergiant

52. And a supernova remnant nebula red supergiant