p7.4 pt 2

Question 1

11. What happens in the formation of a protostar?

Answer 1

-cloud of dust and gas (hydrogen and helium)= contract by gravity= dense= protostars

Question 2

12. What happens when the cloud of gas forming protostars collapses?

Answer 2

-its temperature increases (and pressure) as its volume decreases

Question 3

13. What provided a possible explanation of the Sun’s energy source?

Answer 3

-nuclear processes discovered in the early 20th Century provided a possible explanation of the Sun’s energy source

Question 4

14. What is nuclear fusion?

Answer 4

-when, if brought close enough together, hydrogen nuclei can fuse into helium nuclei releasing energy

Question 5

16. What happens when light nuclei fuse to make heavier nuclei with masses up to that of the iron
    nucleus?

Answer 5

-energy is liberated

Question 6

17. What does everything stand for in Einstein’s equation E = mc2?

Answer 6

• E is the energy produced
• m is the mass lost
• c is the speed of light in a vacuum

Question 7

17. What is used to calculate the energy released during nuclear fusion and fission?

Answer 7

-Einstein’s equation E = mc2

Question 8

18. What happens to the more massive stars?

Answer 8

-the more massive the star, the hotter its core and the heavier the nuclei it can create by fusion

Question 9

19. What is the significance of the core of a star?

Answer 9

-it is where the temperature and density are highest and where most nuclear fusion takes place

Question 10

20. How is energy transferred from core to surface in a star?

Answer 10

• by photons of radiation

- by convection

Question 11

21. What is the significance of the photosphere?

Answer 11

-energy is radiated into space from the star’s surface (photosphere)

Question 12

21. What is the stars surface called?

Answer 12

-photosphere

Question 13

22. What is the Hertzsprung-Russell diagram?

Answer 13

-a plot of temperature (highest to lowest) and luminosity (lowest to highest)

Question 14

22. Where are supergiants located on the Hertzsprung-Russell diagram?

Answer 14

-top right

Question 15

22. Where are giants located on the Hertzsprung-Russell diagram?

Answer 15

-top right

Question 16

22. Where are main sequence stars located on the Hertzsprung-Russell diagram?

Answer 16

-diagonal from top left to bottom right

Question 17

22. Where are white dwarfs located on the Hertzsprung-Russell diagram?

Answer 17

-bottom left

Question 18

22. Why are supernovas not on the Hertzsprung-Russell diagram?

Answer 18

-they happen to quickly, and are not a stable part of the stars life cycle

Question 19

23. Where does hydrogen fusion to helium take place in in main sequence stars?

Answer 19

-in the core

Question 20

24. When does a star leave the main sequence? What happens next?

Answer 20

-when its core hydrogen runs out; it swells to become a red giant or supergiant and its photosphere cools

Question 21

25. What happens in a red giant or supergiant star?

Answer 21

-helium nuclei fuse to make carbon, followed by further reactions that produce heavier nuclei such as nitrogen and oxygen

Question 22

26. What is an example of a low mass star?

Answer 22

-the sun

Question 23

26. What happens to a low mass star at the end of its life?

Answer 23

-becomes a red giant, which lacks the mass to compress the core further at the end of helium fusion; it then shrinks to form a white dwarf

Question 24

27. What happens in a white dwarf star?

Answer 24

-there is no nuclear fusion; the star gradually cools and fades

Question 25

28. What is the mess of a high mass star?

Answer 25

-several times the mass of the Sun

Question 26

28. What happens to a high mass star at the end of its life?

Answer 26

-in a high-mass star nuclear fusion can produce heavier nuclei up to and including iron; when the core is mostly iron, it explodes as a supernova creating nuclei with masses greater than iron and leaving a dense neutron star or a black hole

Question 27

29. What have astronomers found convincing evidence of?

Answer 27

-planets around hundreds of nearby stars

Question 28

30. What may scientists think if even a small proportion of stars have planets?

Answer 28

-that it is likely that life exists elsewhere in the Universe

Question 29

31. What evidence of extraterrestrial life has been found?

Answer 29

-no evidence of extraterrestrial life (at present or in the past) has so far been detected.