End Stages of Stars

1. What brings a star to the end of its life?
A)... It begins to spin so slowly that it collapses..
B)... It runs out of fuels it can "burn. "
C)... All its magnetic energy leaks away.
D)... It eventually collides with another star and smashes to pieces.
E)... It gets sucked into a black hole.

2. What is the last fuel the Sun will be able to burn ?
A)...Hydrogen.
B)...Helium.
C)...Neon.
D)...Iron.
E)...Uranium.

3. What chemical element does the Sun make in burning its last fuel?
A)...Helium.
B)... Carbon.
C)...Neon.
D)...Silicon.
E)...Iron.

4. What happens to a low mass star when it finally uses up the helium in its core?
A)...It begins to burn iron.
B)... It simply cools and dims.
C)...It ejects its outer layers.
D)...The core collapses and it blows up as a supernova.
E)...The whole star collapses and becomes a neutron star.

5. What do astronomers call the shell of ejected gas from certain low mass stars?
A)..A planetary nebula.
B)..A Supernova.
C)..A bipolar flow.
D)..A protostar.
E)..A Cepheid variable.

6. What happens to the core of a low mass star that ejects its outer layers.?
A)...It becomes a black hole.
B)... It becomes a neutron star.
C)...It becomes a white dwarf.
D)... It becomes a pulsar.
E)...It becomes a cepheid variable.

7. The density of the Sun is presently about 1 gm/cm3. If the Sun's radius shrank to about the size of the Earth, (About a factor of 100), what would its density be?
A)... About 10 gm/cm3.
B)... About 100 gm/cm3.
C)... About 1000 gm/cm3.
D)... About 106 gm/cm3.
E)... About 10,000 gm/cm3.

8. What is the remnant core of a low mass star like the Sun mostly made of?
A)... Hydrogen.
B)...Helium.
C)...Carbon.
D)...Sulfur.
E)...Iron.

9. What do astronomers think the core of a massive star is made of when it reaches the end of its life?
A)...Hydrogen.
B)...Helium.
C)... Carbon.
D)... Sulfur.
E)...Iron.

10. Why does a massive star end up with a core so different from that of a low mass star?
A)... Its greater gravity allows it to pull the heavier elements to the core, much like has happened in the Earth.
B)...Its greater gravity compresses the core more and makes it hotter, allowing heavier atoms to fuse.
C)...Its greater gravity compresses the core more and makes it cooler, preventing the fusion of heavier atoms.
D)... It contains more matter so it has more iron that can settle out.
E)... Trick Question. There is essentially no difference between the core of high and low mass stars.

11. When a high mass star's core collapses the star _________.
A)...explodes as a supernova.
B)...becomes a white dwarf.
C)... becomes a neutron star.
D)...becomes a black hole.
E)... All of the above except B are possible outcomes.

12. Why are supernova explosions important for our existence?
A)...They heat the interstellar medium and help keep Earth warm.
B)...They liberate from the star's core the heavy elements of which we and Earth are made.
C)...They destroy wandering stars that might otherwise collide with our Sun.
D)...They bathe Earth in x-rays that may have helped life form.
E)...They sterilized the young Earth and allowed life to originate by killing off competing bacteria.

13. If a planetary nebula expands at about 20 km/sec, how big in AU's will it get in 10,000 years? Note: Assume it starts with zero radius and that it expands at a constant speed. You can take the number of seconds in a year to be 3x107 and the number of km in an AU to be 1.5x108.
A)...400 AU.
B)...40,00 AU.
C)...60,000 AU.
D)...3,000 AU.
E)...3 million AU.

14. How does this compare to the size of the Solar System out to Pluto?
A)... About 10 times larger.
B)...100 times smaller.
C)...10,000 larger.
D)...10 million times larger.
E)...1000 times larger.

15. When a spinning object changes its size, its rotation rate
A)...remains the same.
B)...always increases.
C)...always decreases.
D)... increases or decreases, depending on whether it shrinks or expands.

16. The change in rotation rate of spinning object caused by its size change is a consequence of
A)... conservation of magnetic energy.
B)...the law of action-reaction.
C)... conservation of angular momentum.
D)...the special theory of relativity.
E)...None of the above.

17. The law of conservation of angular momentum states that when an object of a fixed mass changes its radius R, its rotation velocity, V, will change so that
A)...V/R = constant.
B)... VR = constant.
C)...R/V = constant.
D)...V2R = constant.
E)... R2V = constant.

18. If a spinning object's radius shrinks by a factor of 5, its rotation velocity will
A)...get five times faster.
B)... get five times slower.
C)...remain the same.
D)...get 10 times faster.
E)...get 25 times faster.

19. The Sun rotates now with a rotation speed of about 2 km/sec. If its radius shrank to the size of the Earth, about how fast would it spin?
A)...20 km/sec.
B)... 2000 km/sec.
C)...200 km/sec.
D)...0.2 km/sec.
E)...400 km/sec.
20. The Sun at present rotates once per month. If its rotation speed increased by a factor of 100 and its radius shrank by a factor of 100 how often would it spin? Hint: A month is about 5x104 minutes.
A)...Once every 5 days.
B)... Once every 5 minutes.
C)...Once every 5 years.
D)...Once every 15 minutes.
E)...Once every 50 minutess.
21. If the Sun were to shrink its radius by a factor of 100 it would be about the size of
A)...the Earth.
B)... Jupiter.
C)...the state of Texas.
D)...a small town.
E)...a house.

The Two beautiful pictures below were taken by David Malin of the Anglo-Australian Observatory.

Helix Nebula Fig A

22. What sort of object is shown in the figure (A) above?
A)...A Cepheid variable.
B)... A planetary nebula.
C)...A supernova remnant.
D)...An accretion disk around a black hole.
E)...A bipolar nebula.
Dying Star FIG B

23. What sort of object is shown in the figure (B) above?
A)...A Cepheid variable.
B)... A planetary nebula.
C)... A supernova remnant.
D)... An accretion disk around a black hole.
E)... A bipolar nebula.

24. Which of the following is responsible for making a pulsar pulse?
A)... Nuclear reactions..
B)... Radiation trapping in its atmosphere.
C)... Vibrations triggered by a companion.
D)... Spinning.
E)... Tidal distortions caused by a companion.

25 What is meant by an accretion disk?
A)... Hot gas ejected from a supernova.
B)... Cold gas falling onto a white dwarf and forming a flat "splotch" on its surface.
C)... Gas orbiting around a black hole or star.
D)... Matter spun off a neutron star as it collapses.
E)... All of the above.

26. Why do astronomers think that some of the x-ray sources they observe are associated with black holes rather than neutron stars in orbit around a normal star?
A)... They can see a tiny black dot with the x-ray telescope.
B)... The mass of the unseen object inferred from its orbital motion is too large to be a neutron star.
C)... The mass of the unseen object inferred from its orbital motion is too small to be a neutron star.
D)... The magnification of the x-rays by the black hole's gravitational lens clearly shows the black hole.


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