1. The Lives of Stars
Sun-Sized and Massive Stars

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

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

4. 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.

5. The mass of a star determines its fate
0.4 – 8 M☉ Stars
Tiny Stars
Brown Dwarf
Red Giant
M☉ Stars
White Dwarf
Supergiant
25 – 100 M☉ Stars
Neutron Star
Supernova
Supergiant
Black Hole

6. The mass of a star determines its fate:
1.The smallest stars (0.08 – 0.5 M☉) 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.

7. Evolution of sun-sized stars
2. Medium-sized (0.5 – 8 M☉) stars such as our Sun burn very slowly. Our sun will burn for another billion years, mostly as a yellow dwarf main-sequence hydrogen-burner, then collapse under the force of gravity.

8. Evolution of sun-sized stars
3a. This collapse will heat the outer hydrogen layers of the sun, which will boil away into space, causing the sun to swell up into a red giant
400 X the diameter of the sun.

9. Evolution of sun-sized stars
3b. This blazing fireball will engulf the 4 inner planets of the solar system, turning them to burnt cinders, with
vaporized oceans and
incinerated forests.

10. Red Giant vs. earth
Final Score
Red Giant - 1
Earth

11. Inside a Red Giant
1) Helium fuses to form Carbon and Oxygen at the Core
Extra heat causes outer shell of hydrogen
to fuse into He and billow out into space

12. Sun – Yellow Dwarf Main Sequence Sirius – Large Main Sequence Star
Red Giants
Vs.
yellow
dwarfs
Arcturus
1.1 M☉
25.7 R☉
Sun – Yellow Dwarf Main Sequence
Sirius – Large Main Sequence Star

13. Evolution of sun-sized stars
4a. After the red giant has finished blowing off its outer shell, a small, dense, very hot star called a white dwarf is left behind.

14. Sun vs. white dwarf
4b. A white dwarf is the size of Earth, but has as much mass as the Sun…

15. Sun vs. white dwarf 4. A white dwarf - the size of Earth,
but as much mass as 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. 16

17. Stars grow and shrink…
Core temp rises and He fuses to make Carbon. 17

18. Stars grow and shrink…
4c. The core of the white dwarf is held up by electron degeneracy pressure: the atoms are packed so tightly that their electron clouds are touching!! 18

19. Stars grow and shrink…
Pressure increases - Atoms’ electron clouds are touching - a white dwarf is formed! 19

20. White Dwarfs

21. Planetary Nebulae
5. The ballooning gases of the red giant will cool down to form a planetary nebula surrounding the white dwarf.

22. Planetary Nebulae
These clouds form as the red giant’s outer shell expands and cools.

23. White Dwarf at the center of a planetary nebula cloud
White Dwarfs
White Dwarf at the center of a planetary nebula cloud

24. Evolution of sun-sized stars
6a. When the white dwarf has used up all of its helium fuel, it will become a dark carbon cinder called a black dwarf –
like a huge black diamond hiding in the night sky.

25. Evolution of sun-sized stars
6b. (Our sun isn’t big enough to make the carbon core start any further fusion reactions.)

26. life cycle of a sun-sized star

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

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

29. The Fate of Massive Stars

30. Evolution of massive stars
Larger stars (8 – 25 M☉) burn brighter and die more quickly in violent cosmic spasms called supernovas.

31. 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.

32. Evolution of massive stars
2. This collapse causes temperatures to jump to 600 million K the star becomes a red supergiant.

33. Maybe as big as 9.0 AU – would swallow up Jupiter!!
Red superGiant
Betelgeuse in Orion
20 M☉ L☉ R☉
Maybe as big as AU – would swallow up Jupiter!!

34. Evolution of massive stars
3. Helium fuses to
make many new elements (as large
as Iron: Z = 26) in a process known as nuclear transmutation.

35. Layers of a Red-Supergiant…

36. …A Huge Element “Factory”

37. Evolution of massive stars
4. The iron core shuts down the nuclear reactions and the star collapses one final time…

38. Evolution of massive stars
5. This final collapse of the core creates incredibly high
temperatures ( 8 billion K )
which trigger a huge thermonuclear blast –
a supernova.

39. Shock Waves Spread Upward

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

41. Supernova 1987A

42. Supernova and Remnant Nebula
After Before
Supernova 1987A

43. s1987A shock waves in 3D

44. Evolution of massive stars
6b. Elements of all shapes and sizes are formed and scattered as well.
Supernova Remnant Cloud

45. Evolution of massive stars
7. In the core of the star, the pressure is so great that electrons are shoved into the nucleus…

46. Evolution of massive stars
7. …where they combine with protons to form neutrons!!

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

48. Evolution of massive stars
[ That mass that weighs
8X more than the sun is
now packed into a ball
about 12 miles across. ]
(shown here next to Manhattan)

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

50. Supernova Remnant cloud

51. Supernova Remnant crab Nebula
1054 A.D.

52. Supernova Remnant crab Nebula
1054 A.D.

53. life cycle of stars

54. life cycle of stars

55. Degenerate matter in stars

56. White Dwarf

58. life cycle of massive stars

59. life cycle of a supernova star
3 to 10

60. Hertzsprung - Russell Diagram
Main Sequence Stars
Stars X the mass of the sun.

61. Hertzsprung - Russell Diagram
Main Sequence Stars
Stars 8 – 25X the mass of the sun turn into Red Supergiants

62. life cycle of a supernova star
red supergiant

63. A star explodes…
red supergiant

64. Forming a neutron star…
red supergiant

65. And a supernova remnant nebula
red supergiant

66. Neutron Star…

67. Supernova Remnant cloud