Handout 2-1a

1. Handout 2-1a Stellar Evolution

2. Why are astronomers not able to observe the entire life of any star? • Because a star typically exists for billions of years. 1

3. What is the Hertzsprung-Russell diagram? • The graph that illustrates the pattern revealed when the surface temperatures of stars are plotted against their luminosity. 2

4. What is the main sequence? • The band that runs diagonally through the Hertzsprung-Russell diagram and extends from cool, dim, red stars at the lower right to hot, bright, blue stars at the upper left. 3

5. What is a nebula? • A: A cloud of gas and dust where a star begins. 4

6. 5 • What is Newton’s law of universal gravitation? • D: All objects in the universe attract each other through gravitational force.

7. Law of Universal Gravitation

8. Gravitational force increases as the mass of an object: • C: increases, or . . . • as the distance between two objects decreases. 6

9. What happens as more matter is pulled into aprotostar? • Gravitational energy is converted into heat energy, and the temperature of the protostar increases. 7

10. What is important about the onset of fusion? • It marks the birth of a star. 8

11. Stars are born (nebular theory) • They all start like our sun converting hydrogen into helium by high temperature and nuclear fusion Life Cycles of Stars

12. White dwarf then black dwarf? Planetary nebula Star like our sun Red giant Nebula-gas and dust Protostars Neutron star and/or black hole Massive star Red supergiant Supernova

13. What happens as gravity increases the pressure on the matter within a star? • The rate of fusion increases. 9

14. How long does a main sequence star maintain a stable size? • As long as it has an ample supply of hydrogen to fuse into helium. 10

15. What is the second and longest stage in the life of a star? • C: The main-sequence stage. 11

16. A star that has the same mass as the sun’s mass: • B: Stays on the main sequence for about 10 billion years. 12

17. When does a star enter its third stage? • When almost all of the hydrogen atoms in its core have fused into helium atoms. 13

18. Nucleosynthesis and Fusion Reactions The main process responsible for the energy produced in most main sequence stars is the proton-proton (pp) chain.

19. Red Giant Stars

20. What is a planetary nebula? • A: A cloud of gas that forms around a sun-like star that is dying. 14

21. What is a white dwarf? • C: A hot, extremely dense core of matter leftover from an old star. 15

22. What is a black dwarf? • A: A white dwarf that no longer gives off light. 16

23. An explosion on a white dwarf caused by a pressure build-up is a: • D: Nova 17

24. What effect may a nova have on a star? • A: It may cause it to become many thousands of times brighter. Nova Delphinus 2013 18

25. Describe a supernova and how it differs from a nova. • A supernova is a star that has such a tremendous explosion that it blows itself apart. • Unlike a nova, a white dwarf can sometimes accumulate so much mass on its surface that gravity overwhelms the outward pressure. • The star collapses and is so dense that the outer layers rebound and explode. 19

27. Stars that have masses of more than 8 times the sun’s mass produce supernovas: • C: without needing a secondary star to fuel them. 20

28. What happens to the carbon atoms in a collapsing Massive Star as temperatures rise and fusion begins again? • Carbon atoms in the core of the star fuse into heavier elements such as oxygen, magnesium, or silicon. 21

29. What is a neutron star? • A star that has collapsed under gravity to the point that the electrons and protons have smashed together to form neutrons. 22

30. Describe how a black hole forms. • The remaining core of a star has more than 3 times the mass of the sun. • The star may contract further under its greater gravity. • The force of the contraction crushes the dense core of the star and leaves a black hole. 23

31. Why is locating black holes difficult? • Because black holes do not give off light. • Light cannot escape its gravity. 24

32. The End