1. 12-2 Notes How Stars Shine
Chapter 12, Lesson 2

2. Star Formation
In the beginning, the universe consisted of light elements such as hydrogen, helium, and lithium (produced in the Big Bang).

3. Star Formation
Interstellar space is the space between stars and it is composed of mostly NOTHING.
What little matter is found in interstellar space, consists of gas and dust at very LOW densities.

4. Star Formation
Stars form in a nebula, which is a large cloud of gas and dust in space.

5. Star Formation
In a nebula, density is much greater than interstellar space, and clouds form.
Gravity in a nebula causes matter to form clumps.

6. Star Formation
As particles move closer together in the clumps, temperature increases.
As the clump contracts, it becomes spherical.

7. Star Formation
When it reaches a certain mass, it is called a protostar, which continues to contract and increase in temperature.

8. Star Formation
The protostar begins to rotate and flatten into a disk.

9. Star Formation
After millions of years, the temperature is hot enough for nuclear fusion to occur.

10. Star Formation
When the central mass reaches 8% that of the Sun, it is now called a main sequence star.

11. How long will a star last?
Star Formation
How long will a star last?

12. How Stars Produce Light
Stars emit huge amounts of energy, part of which is visible light.
Energy produced during nuclear fusion passes through the star and is emitted from its photosphere.

13. How Stars Produce Light
In a nuclear fusion reaction, two nuclei combine to form a larger nucleus.

14. How Stars Produce Light
In a star’s core, nuclear fusion fuses 2 hydrogens to form helium.

15. How Stars Produce Light
Energy is released as gamma rays and neutrinos.

16. How Stars Produce Light
Fusion reactions produce outward pressure and cause expansion.

17. How Stars Produce Light
Gravity pulls particles toward each other and causes contraction.

18. How Stars Produce Light
The length of a star’s life is determined by the balance of these forces.

19. How Stars Produce Light
Eventually a star converts all its hydrogen to helium, and starts to run low on fuel.

20. How Low-Mass Stars End
Fusion will continue to convert helium into carbon, nitrogen, and oxygen.
These stars will live longer than high-mass stars.
Our Sun is a low-mass star.

21. How Low-Mass Stars End
When fusion stops, there is no longer any force to balance gravity, and the star expands into a red giant.

22. How Low-Mass Stars End
The size of the current Sun (now in the main sequence) compared to its estimated size during its red giant phase in the future.

23. How Low-Mass Stars End
NGC 2392 (about 4,200 light years from Earth) is a star like the sun that was recently photographed becoming a red giant by shedding its outer layers.
X-rays from Chandra (pink) shows superheated gas around the dense, hot core of the star.
The star begins to cool and expand.
Eventually, the outer layers of the star are carried away by a 50,000 km/hr wind, leaving behind a hot core.
This hot core has a surface temperature of about 50,000 degrees Celsius, and is ejecting its outer layers in a much faster wind traveling six million km/hr.
Our Sun will do this about 5 billion years from now.

24. How Low-Mass Stars End

25. How Low-Mass Stars End
After a few billion years, red giants will use up all the fuel in their core.
They will lose all mass from their surface, leaving behind only the core.

26. How Low-Mass Stars End
Now the star spends the rest of its “life” as a white dwarf.
If it cools long enough, it becomes a black dwarf, but no star has cooled long enough to do this.

27. How Low-Mass Stars End

28. How Low-Mass Stars End

29. How High-Mass Stars End
In very massive stars, fusion reactions continue to produce heavier elements, but will die sooner.

30. How High-Mass Stars End
High-mass stars will expand into supergiants.

31. How High-Mass Stars End
supergiant
supergiant
giant

32. How High-Mass Stars End

33. How High-Mass Stars End
Next, a supernova forms when the supergiant explodes before dying.

34. How High-Mass Stars End
How long is the supernova explosion?
The explosion itself is over within a matter of seconds.
But the envelope of the dying star is expelled at high speeds, and as it crashes through interstellar gas, it is heated to millions of degrees and remain bright for tens of thousands of years.

35. How High-Mass Stars End
Supernova remnant:

36. How High-Mass Stars End
Now you see it ... now you don't. Two images of the supernova in Large Magellanic Cloud during (left) and before (right) the explosion.

37. Did you know... at its brightest, an exploding star radiates as much energy in a single DAY...
... as the Sun has in the past 3 MILLION years.

38. How High-Mass Stars End
After the supernova explosion, the leftover matter will either become a neutron star or a black hole.

39. How High-Mass Stars End
Smaller high-mass stars become neutron stars.

40. How High-Mass Stars End
Neutron stars are the very dense remains of stars after a supernova.

41. How High-Mass Stars End
A neutron star is about 6 miles across, but with the same mass as our Sun!

42. How High-Mass Stars End
If you happen to find yourself on the surface of a neutron star, you would weigh ~100,000,000,000 times more than you do now.

43. How High-Mass Stars End
Larger high-mass stars become black holes.

44. How High-Mass Stars End
Black holes are created when a neutron star collapses and all its mass is concentrated into a single point.

45. How High-Mass Stars End
The gravitation force in a black hole is so great not even light can escape.
Black holes can be detected by their influence on other nearby objects.

47. Interstellar space is composed of mainly ____. A nothing B iron
12.2 How Stars Shine A B C D
Interstellar space is composed of mainly ____.
A nothing
B iron
C hydrogen
D dust

48. 12.2 How Stars Shine A B C D
Which type of star has a density so great that protons fuse to electrons?
A red giant
B supernova
C neutron star
D white dwarf

49. In nuclear fusion, smaller nuclei fused to form ____. A hydrogen
12.2 How Stars Shine A B C D
In nuclear fusion, smaller nuclei fused to form ____.
A hydrogen
B helium
C lighter elements
D larger nuclei

50. A supernova could result in the formation of a ____. A supergiant B C D
A supernova could result in the formation of a ____.
A supergiant
B neutron star
C red giant
D white dwarf

51. Our sun will eventually become a ____. A white dwarf B black hole
C neutron star
D dark planet

52. A B C D
The process by which hydrogen is changed to helium in the core of a star is called ____.
A nuclear fission
B nuclear reaction
C nucleolus
D nuclear fusion

53. A moons, planets, and comets B moons, comets, and stars
The following set contains only objects that shine as a result of reflected light:
A moons, planets, and comets
B moons, comets, and stars
C planets, stars, and comets
D planets, stars, and moons